ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V003T00A001. doi:10.1115/IMECE2015-NS3.

This online compilation of papers from the ASME 2015 International Mechanical Engineering Congress and Exposition (IMECE2015) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Advances in Biomedical Elastography

2015;():V003T03A001. doi:10.1115/IMECE2015-51120.

Electrically sensitive polyvinyl alcohol (PVA) hydrogels loaded with methotrexate (MTX) were prepared via a solution casting process, and characterized by attenuated total reflectance (ATR) spectrometry. In order to determine if the hydrogels were electro-sensitive or not, bending tests were conducted on the sulfoacetic acid modified hydrogels. It was observed that the prepared samples into strip forms started bending towards the cathode, and this bending was reversible when the polarity of the applied voltage was changed. The drug release study was performed on the MTX-loaded hydrogel strips placed in a sodium chloride (NaCl) solution under three different voltages (e.g., 0V, 5V, 10V, and 20V). Subsequently, the solutions were collected every five minutes in order to determine the drug release behaviors of the hydrogels using an ultraviolet-visible (UV-Vis) spectrophotometer. The test results showed that sulfoacetic acid (SA)-modified PVA hydrogels possess electrical sensitive behavior and kept their electric sensitivity for a long period of time. Also, the results confirmed that the control drug release could be achieved under different electrical voltages.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Bioinspired Materials and Structures

2015;():V003T03A002. doi:10.1115/IMECE2015-50962.

Bioinspired materials have enabled the fabrication of tough lightweight structures for load- and impact-bearing applications of which an example is fiber-reinforced plastics use in aerospace. If applied to the field of construction, biomimicked composites can save lives, otherwise lost to earthquakes and other disasters that cause collapse of buildings. The main culprit is the low resistance of structures exposed to dynamic shear stresses, typical of earthquakes. Recent work on the application of biomimicry to structural composites has clearly shown the advantage of these materials in resisting dynamic shear. Adding natural or synthetic reinforcement fibers may alleviate the need for conventional steel rebars and make it possible to print buildings by conventional 3D printing technology. The main hurdles are to find the right type of composite that is compatible with 3D printing and the right process for deposition of such material. In the past, combination of carbon fiber, glue and concrete has been demonstrated to enhance the toughness of resulting structural composites. Inspired by the microstructure of oyster and mother of pearl, layering of these materials mitigates the localization of deformation by distributing the imposed displacement over a large area. The intricate structure of these layers, and the minute details of the interfaces are important for affecting good dynamic shear resistance. In nacre, a partial slip of sandwiched layers occurs before it stops and deformation is transferred to the adjacent area. This energy-absorption capability underlies the high-toughness behavior of nacre and similar structures. By mimicking nacre, bone and tooth, it is possible to benefit from their good properties, however, it is important to determine the type of material, layering scheme, geometry, and other factors that affect mechanical properties. A recently-developed medium-sized 3D printer was developed to deposit structural materials. These include cement, plaster, polymer and clay. Combinatorial structural composite research (CSCR) comprising the simultaneous fabrication and characterization of multiple specimens with different microstructures allows fair comparison of mechanical properties of various structural composites. Novel application of deposition techniques to the extrusion of plaster, cement and clay paves the way to layer these materials along with glue and fibers in desired schemes. Use of ANOVA tables in the selection of various types of ceramics, polymers and reinforcement materials for the fabrication of different composites will be discussed. In addition to selection of the type of the materials, deposition schemes such as those of solid and hollow structures, different layer thickness applications, and the effect of timing will be elucidated. Microscopy conducted on the fractured surfaces enables the investigation of the mechanisms of fracture and failure for these CSCR composites. The details of experiments conducted, microscopy performed and the results of mechanical tests will be presented.

Commentary by Dr. Valentin Fuster
2015;():V003T03A003. doi:10.1115/IMECE2015-51091.

This paper examines the implementation of Nitinol wire as a complex-shape actuation source specifically targeted for low-power muscle biomimetics. Nitinol is a type of shape memory alloy (SMA) which recovers its original shape after experiencing large deformation when heated above an austenite finish temperature. Previous preliminary work by the authors demonstrated successful closed-loop force control (i.e., recovery stress) using a simple proportional controller. The work presented in this paper builds upon the previous work by demonstrating closed-loop position control of various wire arrangements in the presence of inertial loads. A predeformed NiTi (4% pre-strain) wire is energized via Joule heating (martensite to austenite) and de-energized by conductive cooling (austenite to martensite). The experimental setup consists of a horizontally arranged NiTi wire (or wire bundle) fixed at one end and connected to a hanging weight through a pulley on the opposite end. The angular displacement of the pulley is measured with a non-contact magnetostrictive angle sensor, thereby providing the control feedback signal for the wire displacement. Successful closed-loop position control is demonstrated, and the relative ease of control is assessed for increasing weights. Given the dynamic loading of the moving wire, a proportional controller alone is insufficient to obtain stabilized responses. Therefore, PID with anti-windup method is employed. Although PID requires some trial and error and is quite sensitive to varying conditions, it appears to be stable and sufficiently precise when properly tuned. The effect of bundling wires on the speed of response is experimentally characterized, and different bundling arrangements are designed and examined in order to increase the geometric rate of convective heat transfer. Increasing the rate of heat transfer is particularly important during the forward (austenite-to-martensite) transformation, since its speed relies solely on passive cooling of the wires. Limitations in controlled load capabilities are discussed in the context of wire diameter, bundle size and controller tuning. A repeatability study of a properly tuned PID controller is also carried out by comparing the first few and last few samples of a 50,000-cycle test. In addition, it is shown that identical wires, when swapped, do not require re-tuning of the PID gains. Finally, this paper shows some preliminary actuator designs that can mimic complex muscle movement. Various geometric arrangements of Nitinol wires are embedded into a curable elastomer with skin-like flexibility and durometer. The potential facial muscle movements from these arrangements are shown and discussed.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Biological Tissues and Materials: Modeling, Synthesis and Characterization

2015;():V003T03A004. doi:10.1115/IMECE2015-50003.

Cardiovascular diseases account for one third of all deaths worldwide, more than 33% of which are related to ischemic heart disease, involving a myocardial infarction (MI). Following myocardial infarction, the injured region and ventricle undergo structural changes which are thought to be caused by elevated stresses and reduction of strains in the infarcted wall. The fibrotic phase is defined as the period when the amount of new collagen and number of fibroblasts rapidly increase in the infarcted tissue. We studied through finite element analysis the mechanics of the infarcted and remodeling rat heart during diastolic filling. Biventricular geometries of healthy and infarcted rat hearts reconstructed from magnetic resonance images were imported in Abaqus©. The passive myocardium was modelled as a nearly incompressible, hyperelastic, transversely isotropic material represented by the strain energy function W = ½C(eQ − 1) with Q = bfE112 + bt(E222 + E332 + E322) + bfs(E122 + E212 + E132 + E312). Material parameters were obtained from literature [1]. As boundary conditions, the circumferential and longitudinal displacements at the base were set to zero. The radial displacements at the base were left free. A linearly increasing pressure from 0 to 3.80 kPa and 0.86 kPa, respectively, was applied to the endocardial surfaces of left and right ventricle. Average radial, circumferential and longitudinal strains during passive filling were −0.331, 0.135, 0.042 and −0.250, −0.078 and 0.046 for the healthy heart and the infarcted heart, respectively. The average radial, circumferential and longitudinal stresses were −1.196 kPa, 3.87 kPa in the healthy heart and 0.424 kPa and −1.90 kPa, 8.74 kPa and 1.69 kPa in the infarcted heart. The strains were considerable lower in the infarcted heart compared to the health heart whereas stresses were higher in the presence of an infarct compared to the healthy case. The results of this study indicate the feasibility of the models developed for a more comprehensive assessment of mechanics of the infarcted ventricle including extension to account for cardiac contraction.

Commentary by Dr. Valentin Fuster
2015;():V003T03A005. doi:10.1115/IMECE2015-50004.

The physiological basis of the right ventricle diastolic function is not well studied. In most heart failure, heart transplantation remains the first choice with survival ranges between 40% and 50%. It is known that heart transplantation lacks donors and therefore, there is a need to search for new surgical techniques for heart failure prevention. This study utilized the finite elment method to study the structural behavior of heart wall under severe pressures. In this study the effect RV filling during over-pressurised RV using bi-ventricular model has been studied using finite element modeling (FEM). Cardiovascular disease (CVD) is the leading cause of death in low-income and middle-income countries. The right ventricle (RV) dysfunction is understood to have an impact on the performance of the left ventricle (LV) but the mechanisms remain poorly understood. Finite strain analyses of bi-ventricular model provide important information on the heart function. The passive myocardium was modelled as a nearly incompressible, hyperelastic, transversely isotropic material. Biventricular geometries of healthy and infarcted rat hearts reconstructed from magnetic resonance images were imported in Abaqus©. In simulating the passive filling of the healthy condition of the rat heart, the inner walls of the LV and RV the pressures of 4.8 kPa and 0.0098 kPa were applied respectively. The average circumferential strain was found to be 0.138 and 0.100 on the endocardium of the over-pressured and healthy model respectively. The high stresses and strains on the over-loaded model were observed.

Commentary by Dr. Valentin Fuster
2015;():V003T03A006. doi:10.1115/IMECE2015-50906.

An investigation into the effect of extraosseous formation around an internal fixation plate (long bone mid-shaft) and callus ossification on the localalized stress distribution in the periosteum is performed. An analytical model of the system is developed; predicted trends are compared with Finite Element (FE) model predictions. Both models are described and the limitations relevant to their predictions are discussed. Two load cases are examined: pure bending and bending coupled with compression. Both models indicate that the presence of the plate results in stress shielding for both load cases. For the pure bending case, the analytical model predicts that the extraosseous formation serves to reduce the level of stress shielding caused by the plate, while the FE model predicts an increase. Both models predict that the presence of callus serves to further increase stress shielding, however the magnitude of the effect of the callus on the tension side of the bone differs substantially between models. Further refinement of both models is recommended.

Commentary by Dr. Valentin Fuster
2015;():V003T03A007. doi:10.1115/IMECE2015-51112.

Anisotropy exists in many soft biological tissues. The most common anisotropy is transverse isotropy, which is typical for fiber-reinforced structures, such as the brain white matter, tendon and muscle. Although many methods have been proposed to determine tissue properties, techniques to characterize transversely isotropic materials remain limited. The goal of this study is to investigate the feasibility of asymmetric indentation coupled with numerical optimization based on inverse finite element (FE) simulation to characterize transversely isotropic soft biological tissues. The proposed approach combining indentation and optimization may provide a useful general framework to characterize a variety of fiber-reinforced soft tissues in the future.

Commentary by Dr. Valentin Fuster
2015;():V003T03A008. doi:10.1115/IMECE2015-51153.

Osteochondral tissue has a graded structure spanning from the subchondral bone region beneath the joint surface to the hyaline cartilage region at the joint surface. Biological, physiological, and mechanical properties over the regions cross-section vary greatly; this provides a significant challenge for tissue-engineered structures addressing osteochondral defects. The objective of this research is to investigate the effects of scaffold pore structure on mechanical, biological, and physiological properties of 3D printed tissue engineered osteochondral scaffolds. Our results indicate that gradient pore structures improve both mechanical properties and cell performance when compared to homogeneously distributed pores and non-porous structures. This study also indicates that including nanocrystalline hydroxyapatite (nHA) into the hydrogel scaffold further improves cellular performance compared to both porous scaffolds without nHA and nonporous scaffolds.

Commentary by Dr. Valentin Fuster
2015;():V003T03A009. doi:10.1115/IMECE2015-51193.

Targeted drug delivery systems have been shown to be promising alternative for the conventional drug delivery methods. Among numerous nanocarriers developed for therapeutic applications, iron oxide magnetic nanoparticles have attracted considerable attention. Fe3O4 (magnetite) is one of the most commonly used iron oxide in biomedical applications due to its biocompatibility and can be easily produced in research and industrial laboratories. The core/shell structure of magnetic nanoparticles allows the surface coating to avoid their agglomeration. Moreover, coating of Fe3O4 nanoparticles provide functional groups and consequently make the bioconjugation to the therapeutic agents. Coating magnetic nanoparticles with a biopolymer will also increase biocompatibility. Coating magnetic nanoparticles with a biopolymer will also increase biocompatibility. Chitosan can easily conjugate to the surface of magnetic nanoparticles and provide amine and hydroxyl groups for the further conjugation of the therapeutic drug. In this study, Fe3O4 magnetic nanoparticles were fabricated and were coated with chitosan via in-situ method. Prepared chitosan coated magnetic nanoparticles then were loaded with methotrexate (anti-cancer drug) through adsorption. The size and morphology of synthesized magnetic nanoparticles were evaluated using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The chemical structure of bare and chitosan coated magnetic nanoparticles was analyzed by Fourier Transforms Infrared (FTIR). Methotrexate loading efficiency of chitosan coated nanoparticles was also evaluated. Cytotoxicity of nanoparticles was also studied in-vitro. The results confirmed the surface coating with chitosan and methotrexate loading. The synthesize chitosan coated magnetic nanoparticles showed promising application for cancer treatment.

Commentary by Dr. Valentin Fuster
2015;():V003T03A010. doi:10.1115/IMECE2015-51235.

The purpose of this study is to develop a novel bone replacement using in situ polymerization of thiol-acrylate with adipose tissue derived adult stem cells (ASCs). Specifically, Poly(ethylene glycol) diacrylate-co-trimethylolpropane tris (3-mercaptopropionate) (PEGDA-co-TMPTMP) was synthesized with 10% Hydroxyapatite (HA) foam by an amine-catalyzed Michael addition reaction. Initial characterization studies were performed to determine the temperature profile during the exothermic reaction showing a peak temperature of 50°C. To prevent hyperthermic cell damage and death during the exothermic polymerization procedure, the hASCs were encapsulated in alginate. Characterization of the 3-D structure and interconnectivity of pores in the polymeric foam scaffolds were performed using FIB-SEM and Micro-CT showing uniform distribution of HA. Cell viability experiments within the polymeric scaffold were performed using Vybrant® MTT cell profileration method, as well as fluorescent dyes: Calcein-AM (live) and Ethidium homodimer-1 (dead) showing viability of cells inside the samples.

Topics: Bone , Polymerization
Commentary by Dr. Valentin Fuster
2015;():V003T03A011. doi:10.1115/IMECE2015-51906.

Bio-degradable Poly (l-lactic acid) (PLLA) scaffolds synthesized using thermally induced phase separation (TIPS) method was used to load cryo-preserved human adipose derived stem cells (hASCs). To make the scaffolds, PLLA-Dioxane solutions were formed by dissolving PLLA in 1,4-Dioxane with three different compositions (wt/vol). These PLLA-Dioxane solutions, frozen in three different cooling rates were lyophilized at 0.037bar and −70°C for 48hrs resulting in porous PLLA scaffolds. Based on the porosity, pore size and compressive strength, a suitable scaffold was chosen to investigate its bio-compatibility and osteo-inductive potential.

Commentary by Dr. Valentin Fuster
2015;():V003T03A012. doi:10.1115/IMECE2015-51933.

Advancement in materials science and manufacturing processes helps in expanding the application span of materials in biotechnology. The technological development of biocompatible materials aids in improving health conditions, cancerous treatment, organ implants, and as well as provides several techniques to patient treatment. Hydroxyapatite (HAP) is considered as a potential material for orthopedics and dental implants due to its eminent biocompatibility and natural apatite characteristics. It is regarded as viable and cost effective solution of many biomedical applications. Major challenges in expanding the application span of HAP include obtaining optimum mechanical, chemical, and biological properties simultaneously while making its manufacturing processes cost effective. The main purpose of the current work is to synthesize and characterize high strength HAP with high degree of crystallinity and purity, which could be able to fulfill the requirements of modern biological materials. In this work, egg-shell which is considered as garbage is utilized as calcium source to synthesize HAP. Initially, egg-shells are properly cleaned with distilled water and dried. Ball milling operation is used to produce egg-shell particles of nano to micron range. The particles then mixed with controlled amount of phosphoric acid. The mixture is then sintered by heat treating at 900°C for 2 hours. The heat treatment (sintering) process is used to enhance the density as well as strength of egg-shell material. After synthesis of HAP, it is characterized through X-ray diffraction, scanning electron microscopy, and laser particle analyzer. Composition of HAP is investigated through XRD. Furthermore, surface topography of nano-crystalline HAP powder is measured through Scanning Electron Microscope while particle size distribution is found through laser particle analyzer. It is found that the addition of phosphoric acid in milled egg-shell and heat treatment give rise HAP in the sample. In addition, particle size varies from hundreds of nanometers to several micrometers. The results and analysis of the current work may provide insight of different properties which may lead to the development of optimum and cost effective HAP material. The current study could be further extended in increasing application envelop of biocompatible materials.

Topics: Shells
Commentary by Dr. Valentin Fuster
2015;():V003T03A013. doi:10.1115/IMECE2015-52318.

Hip fracture is one of the most serious and common health problems among elderly which may lead to permanent disability or death. Hip fracture commonly occurs in the femoral bone, the major bone in the hip joint. Microscopic age-related changes in the structure of cortical bone is one of the factors that is considered to be partially responsible for the increase of fracture risk in elderly. It is of great interest to develop a predictable model of such fractures for the aging population in preparation of a suitable therapy. These micro structural changes influence mechanical properties and, therefore, behavior of bone and are critical to understand risk and mechanics of fracture of bone. Correlation between cortical bone strength and porosity, as a microscopic structural factor, has been examined frequently as a function of age and/or porosity. These studies have investigated the effect of porosity experimentally and have not studied the effect of porosity independently from other structural factors such as bone mineral density. In this study effect of porosity on elastic properties of human femoral cortical bone was studied independently using finite element analysis assuming transversely isotropic behavior in terms of elastic properties with the axis of elastic properties along the longitudinal axis of femur shaft. In this study, published standard mechanical tests for transversely isotropic materials were simulated using finite element computer simulation on models with different porosities. The developed finite element model utilized material properties based on the best fit regression in previously published articles. Pores’ size, shape and distribution were also modeled based on previous experimental studies. The finite element model, in general, predicted behavior of five independent elastic mechanical properties, namely, longitudinal Young’s modulus, transverse poisson’s ratio, transverse shear modulus, transverse Young’s modulus and longitudinal poisson’s ratio, as a function of porosity. Furthermore, effect of porosity on the elastic properties across various age groups was investigated using published data on age-related changes in bone porosity. Mathematical models based on Finite Element Analysis results have been developed using linear least square regression. These models show negative linear relationship between studied elastic properties of human femoral cortical bone and porosity. The Finite Element Analysis results compared well with the previously published experimental data. Furthermore, the results obtained show the elastic properties as functions of age for females and males. The predicted values for elastic properties are lower for men compared to women of age 20 to 40 years old. However, after the age of 44, elastic properties of femoral cortical bone for men are higher than women. The Finite Element Model developed in this study will help to create a clinical bone model for the prediction of fracture risk or the selection of suitable therapy in orthopedic surgery.

Topics: Elasticity , Bone , Porosity
Commentary by Dr. Valentin Fuster
2015;():V003T03A014. doi:10.1115/IMECE2015-52585.

Electrospun fibers made of biocompatible polymers have been used as scaffolds in tissue engineering to mimic the fibrous environment found in the extracellular matrix (ECM) of biological tissue; and bioactive macromolecules can also be encapsulated in the electrospun fibers. In order to control the release of these encapsulated macromolecules, it is of great interest to understand how the release rate is affected by the sizes of molecules, cross-linking as well as electrospinning configuration (single axial versus co-axial). Fluorescein imaging technique has been applied in quantifying molecular transport phenomena. This paper presents an image analysis method to establish a baseline correlation between the fluorescent intensity and the macromolecule concentration in the electrospun fibers. In this study, alginate and Poly(ethylene oxide) (PEO) blend polymer aqueous solution (1:1 ratio, 3% w/v) was used to electrospin fibers and fluorescein-isothiocyanate dextran (FITC-dextran) with different molecular weights was chosen as the encapsulated macromolecule. Linear correlation was established based on the statistical analysis of electrospun fiber images, and imaging parameters effects were also identified.

Commentary by Dr. Valentin Fuster
2015;():V003T03A015. doi:10.1115/IMECE2015-52878.

Tissue-mimicking materials (TMM) are often used as surrogates for human tissue when developing prospective treatments such as thermal ablation of tumors. Localized heating or ablation may be applied by methods including high-intensity focused ultrasound (HIFU), radio frequency (RF), microwave, and laser treatment. In such methods, confining the heated region to a narrow target is an important concern for minimizing collateral damage to surrounding healthy tissue. Mechanical compression can potentially assist in confining heat near a target region by constricting microvascular blood flow. However, characterization of the effects of compression on thermal properties of the tissue itself (apart from microvasculature) is needed for accurate modeling of heat transfer. Accordingly this study presents a method and material characterization results that quantify the extent to which mechanical compression alters thermal conductivity, specific heat capacity, and thermal diffusivity of a polyacrylamide-based TMM.

Cylindrical test specimens were cast from polyacrylamide material with diameter of 50 mm and height of 45 mm. Compression was applied using custom apparatus for applying prescribed uniaxial displacement, with a modular configuration for testing under ambient temperature as well as on a hot plate. Compression force at room temperature was measured with a load cell that was positioned in-line between compression plates. Prescribed heat flux was delivered based on power input, as quantified with the use of a reference sample in a thermal resistance network. Temperature was measured by an array of thermocouples. Software simulations were performed using finite element analysis (FEA) for structural deformation and computational fluid dynamics (CFD) for heat transfer under the combined effects of conduction and convection. The simulations provided estimates of deformed shape and thermal losses that were compared to experimental measurements.

Mechanical stress-strain tests using three TMM replicate specimens at room temperature showed a linear stress-strain relationship from approximately 2% to 14% strain and a compressive modulus of elasticity ranging from 7.56 kPa to 12.7 kPa. Distributed temperature measurements under an imposed heat flux resulted in thermal conductivity between 0.89 W/(m·K) and 1.04 W/(m·K), specific heat capacity between 5590 J/(kg·K) and 6720 J/(kg·K) and thermal diffusivity between 1.29 × 10−7 m 2 /s to 1.71 × 10−7 m2/ s. Viscoelastic effects were observed to reach steady state after approximately 20 seconds, with full elastic recovery upon unloading. Thermal conductivity and thermal diffusivity were observed to decrease under mechanical compression, while specific heat capacity was observed to increase. The results affirm that thermal properties of tissue-mimicking material can be altered by mechanical compression. These findings can be applied to future investigation of temperature distribution during localized ablation by methods such as HIFU, and can be extended to refined material modeling of perfused tissue under compression.

Commentary by Dr. Valentin Fuster
2015;():V003T03A016. doi:10.1115/IMECE2015-53398.

Segmental bone defects result in isolated bone fragments. These defects may be caused by trauma or disease and are a leading cause for orthopedic surgery. Segmental defects pose a challenge as they contain gaps between the ends of bones, which are too large for the regenerating tissue to naturally bridge and repair. A widely used clinical approach to repair such defects is the use of autografts that provide the essential bone growth features. However, autografts generate a secondary deficit in the region from which the graft was harvested. This grafting procedure may result in other complications, such as infections, inflammation, scarring, and bleeding. Synthetic bone scaffolding has been explored as a viable method of helping the body repair segmental bone defects. While synthetic bone scaffolding is a promising approach in orthopedic treatments, limitations exist. Bone is a complex organ with many cell types, emergent, anisotropic, mechanical properties and molecular interactions. Studies have shown that the inner geometries, such as pore size, play an integral role in bone regeneration, cell proliferation, differentiation and recovery. An architecturally-based approach in the design and fabrication of the scaffold may support the differentiation of complex bone tissues.

This study developed and tested scaffold designs having different pore size and beam thickness. The designs were developed and simulated for compression and tension in SolidWorks. A hexagonal unit cell was the basis for scaffold design. In one experimental trial (Group 1), the offset of the layers was varied. In another experimental trial (Group 2), the ratio between pore size and beam thickness was varied while using the optimal offset from the former trial. The material for simulation was poly-L-lactic (PLA) acid.

In the analysis of the simulation results, the optimal layer offset configuration of 100%,50% in the positive x-y direction showed the lowest stress distribution for both compression and tensile simulations compared to the other offset configurations analyzed. In the second trial of Group 2 models, two models with pore size to beam thickness ratios (7:1 and 8:1) demonstrated low stress distribution under the simulated physiological environments. These results suggest that both models can potentially have different applications in the repair of segmental bone defects.

Commentary by Dr. Valentin Fuster
2015;():V003T03A017. doi:10.1115/IMECE2015-53686.

Titanium (Ti) and Ti-based alloys are widely used as implants for hard tissue repair. However, the optimal surface properties for ideal integration of Ti implant with native tissues have not yet been achieved. The goal of this study was to improve the bio-mechanical performances of titanium (Ti) implant by implant surface modification such as coating fiber on the implant surface. It is hypothesized that deposition of fiber with certain architecture can increase mechanical interlock of Ti surface which leads to the increment of in vitro bonding of Ti/cement interfaces. The research objectives were to (1) test the fracture strength of Ti-cement with one round, two rounds and five rounds of PCL fiber under static load to determine the topology effect of electrospun fiber material on the Ti/PMMA cement interface; (2) test the fracture strength of Ti-cement with PCL fiber and PCL-PMMA fiber, with and without heating up Ti before fiber under static load to determine the topography effect of electrospun fiber material on the Ti/PMMA cement interface. PCL and PCL-PMMA fibers coated on the Ti surfaces were produced by electrospinning technique using PCL-acetone fiber solution and PCL-PMMA-acetone solution respectively. Under static conditions, Ti/PMMA union specimen with and without fiber were tested to determine the fracture strength. The result showed one round of PCL fiber has higher fracture strength than two rounds and five rounds of fiber, which suggested that more fibers on the surface were not benefit to the fracture strength of Ti-cement interface. With PMMA added into the polymer fiber solution, the fracture strength of Ti-fiber-cement increased. Heating up the Ti implant to 50°C before coating PCL fiber can help the PCL fiber become stickier to the Ti implant which leads to the increasing of the fracture strength of Ti-cement interface. However, for PCL-PMMA fiber, heating up Ti implant before fiber doesn’t help improve the quality of Ti-cement interface as PCL fiber.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Biomedical Ultrasound

2015;():V003T03A018. doi:10.1115/IMECE2015-50552.

This paper investigates the effect of an ultrasound field on the evaporation of water droplets into an air stream flowing along a conduit. The air and droplet mixture (aerosol) is passed through an intense ultrasound field, generated in a cylindrical sonotrode, in an effort to accelerate the droplet evaporation process. The improvement in droplet evaporation was evaluated by measuring changes in the droplet size distribution and changes to the air humidity and temperature. It was found that at high power levels the droplets were rapidly and completely vaporized. At power levels in the 2–20 W range there was a significant increase in droplet evaporation, up to 28%, but also some droplet coalescence occurred. The mechanism for this improvement was thought to be a result of enhanced convection heat and mass transfer processes and the input of heat energy into the aerosol. This study has demonstrated that an ultrasound field does improve water droplet evaporation.

Commentary by Dr. Valentin Fuster
2015;():V003T03A019. doi:10.1115/IMECE2015-51131.

Recent studies suggest that dual frequency intravascular ultrasound (IVUS) transducers are promising in contrast ultrasound for molecular imaging or vasa vasorum (VV) assessment to identify vulnerable plaques. Low frequency (1–3 MHz) acoustic waves are widely used for contrast imaging because it can excite microbubbles more effectively. However, conventional thickness mode 1–3 MHz transducers are not suitable for IVUS since bulky transducer size is not permitted in fine IVUS catheters used for coronary interventions (approx. 3-French). In this paper, a dual frequency (2.25 MHz/30 MHz) IVUS transducer with a lateral mode transmitter (2.25 MHz) and a thickness mode high frequency receiver (30 MHz) was designed, fabricated and characterized. In contrast detection tests, superharmonic microbubble responses flown through a 200 μm diameter tube was successfully detected with a contrast to noise ratio (CNR) of 13 dB and an axial resolution (−6 dB) of 0.1 μs (150 μm). The results showed that this dual frequency IVUS transducer with a lateral mode transmitter can be used to detect super-harmonic signal (12th to 15th harmonic) ideal for superharmonic imaging of microvascular structures.

Commentary by Dr. Valentin Fuster
2015;():V003T03A020. doi:10.1115/IMECE2015-52540.

Ultrasonography is well known as a relatively low cost and non-invasive modality for real-time imaging. In recent years, various high frequency array transducers have been developed and used for ophthalmology, dermatology, and small animal studies. This paper reports the development of a 48-element 40-MHz ultrasonic array using micromachined lead magnesium niobate-lead titanate (PMN-PT) single crystal 1–3 composite material. Array elements with a pitch of 100-micron were interconnected via a customized flexible circuit. Pulse-echo test showed an average center frequency of 40 MHz and a −6 dB fractional bandwidth of 52%. The −20 dB pulse length was evaluated as 120 ns. The electrical and acoustical separation showed the crosstalk less than - 24 dB. An image of a steel wire target phantom was acquired by stacking multiple A-lines. The results demonstrate resolutions exceeding 70 μm axially and 800 μm laterally. Those results imply the great potential of the developed array transducer for the high frequency medical imaging.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Clinical Applications of Bioengineering

2015;():V003T03A021. doi:10.1115/IMECE2015-50598.

Currently used mechanical heart valve prostheses does not fully restore the function of the valve and require aggressive anticoagulation therapy. One of the reasons leading to the prostheses disfunction is neglecting of hydrodynamic compatibility with the blood flow pattern Studies of the hydrodynamic structure of the blood flow in the heart and aorta are being performed in the Bakulev Center for Cardiovascular surgery since 1992. It has been shown that blood flow, generated in the left ventricle corresponds to the structure of self-organizing tornado-like flows described by the exact solution of unsteady hydrodynamic equations for this class of flows, published in 1986. The previous attempts to adapt the geometry of prosthetic heart valve to the swirling blood flow were not successful since there were no any quantitative criteria of the flow structere. A new model of a mechanical aortic valve — Tornado-compatible valve (TCV) (patent RU 2434604 C1), has the lumen completely free from any kind of obstacles that could disrupt the flow pattern. The valve consists of a body and three cusps which profile is adopted both to the flow in Aorta, and to the flow in Sinuses when the valve is closed. The standard hydrodynamic testing of this valve has shown its significant advantage compared with other valve types. A special testing was developed using the original bench which generates the Tornado-like jet. For this a converging channel was worked out, which profile corresponds to the streamlines of Tornado-like flow, calculated from the exact solution. The resulted jet manifested all principal properties of Tornado: laminar “glass-transparent” jet without any visible perturbations in the flow core. Several valve types were testing using this bench. TCV did not affected the jet structure, and time of water flowing out. The valve was implanted in the pig without anticoagulant administration. According to echocardiography and coagulation control the valve function was satisfactory up to ten months of observation. In the autopsy the luminal surface of outflow part of the left ventricle, and the ascending aorta were free of thrombi and pannus formation. The clinical implantation in the patient with aortic stenosis was performed. The follow-up period is 4 years.

Topics: Prostheses , Valves
Commentary by Dr. Valentin Fuster
2015;():V003T03A022. doi:10.1115/IMECE2015-50875.

This article presents the early results from a 10-person human subject study evaluating the accuracy of a novel method of indirect estimation of intraocular pressure using tactile sensors. Manual digital palpation tonometery is an old method used to estimate the eye pressure through palpation with ones fingers. Based on this concept, we present an instrumented measurement method, where multiple tactile stiffness sensors are used to infer the intraocular pressure of the eye. The method is validated using experimental data gathered from human subjects with eye pressures from 15 to 22 mmHg and determined by Goldman applanation tonometry (GAT). Bland-Altman plots comparing the GAT measurements and the proposed through-the-eye-lid tonometry indicate a statistical error of 5.16 mmHg, within the 95% confidence interval, which compares favorably with the FDA-mandated error bound of 5 mmHg. Details on the unit operation and data filtering are also presented. Due to its indirect and non-invasive nature, the proposed new tactile tonometry method can be applied at home as a self-administered home tonometer for management of glaucoma.

Commentary by Dr. Valentin Fuster
2015;():V003T03A023. doi:10.1115/IMECE2015-51124.

Non invasive fractional flow reserve derived from CT coronary angiography (CT-FFR) has to date been typically performed using the principles of computational fluid analysis in which a lumped parameter coronary vascular bed model is assigned to represent the impedance of the downstream coronary vascular networks absent in the computational domain for each coronary outlet. This approach may have a number of limitations. It may not account for the impact of the myocardial contraction and relaxation during the cardiac cycle, patient-specific boundary conditions for coronary artery outlets and vessel stiffness. We have developed a novel approach based on 4D-CT image tracking (registration) and structural and fluid analysis based on one dimensional mechanical model, to address these issues. In our approach, we analyzed the deformation variation of vessels and the volume variation of vessels to better define boundary conditions and stiffness of vessels. We focused on the blood flow and vessel deformation of coronary arteries and aorta near coronary arteries in the diastolic cardiac phase from 70% to 100 %. The blood flow variation of coronary arteries relates to the deformation of vessels, such as expansion and contraction of the cross-sectional area, during this period where resistance is stable, pressure loss is approximately proportional to flow. We used a statistical estimation method based on a hierarchical Bayes model to integrate 4D-CT measurements and structural and fluid analysis data. Under these analysis conditions, we performed structural and fluid analysis to determine pressure, flow rate and CT-FFR. Furthermore, the reduced-order model based on fluid analysis was studied in order to shorten the computational time for 4D-CT-FFR analysis. The consistency of this method has been verified by a comparison of 4D-CT-FFR analysis results derived from five clinical 4D-CT datasets with invasive measurements of FFR. Additionally, phantom experiments of flexible tubes with and without stenosis using pulsating pumps, flow sensors and pressure sensors were performed. Our results show that the proposed 4D-CT-FFR analysis method has the potential to accurately estimate the effect of coronary artery stenosis on blood flow.

Commentary by Dr. Valentin Fuster
2015;():V003T03A024. doi:10.1115/IMECE2015-51532.

There is discordance between the anatomic severities of the coronary narrowing and their corresponding functional significance. Fractional Flow Reserve (FFR) is among the physiological parameters invasively measured to assess the hemodynamic significance of a stenosis during maximal hyperemia. FFR values ≤ 0.8 indicate that the downstream heart tissue perfused by this vessel is at risk for ischemia. While measuring FFR is an invasive procedure that is expensive, time consuming, and not without complications, recently, noninvasive estimation of FFR was shown to be possible from comprehensive predictive techniques allowing the computation of in-vivo FFR. However, these non-invasive methods are associated with high computational cost and require high performance computing technology, thus, reducing their wide adoption in clinics. This paper is steered to achieve two main goals: (1) to develop a fast numerical method to aid clinicians assessing ischemia level and determine if coronary revascularization (PCI) is required in human diseased coronary arteries with minimum time and computer resources; (2) to develop a robust method which allows predicting the patient FFR independently of the actual in-vivo physiologic conditions (mainly pressure) of the specific patient. The numerical framework was designed by adopting the finite volume method to generate the discrete model of the Reynolds average form of conservation equations used to predict blood hemodynamics. Two strategies were investigated to reduce computational cost while retaining solution accuracy. The first strategy is based on isolating the diseased artery from its branch tree and simulating it separately without implicitly integrating other arterial segments. A lumped dynamic model with special numerical treatment is coupled to the 3D domain outlet boundary to account for the downstream effects from the vascular bed. The second strategy is based on replacing a full transient simulation by a steady state one performed under mean conditions of pressure and blood volume flow rate. The strategy was applied on a healthy (hypothetical) and stenosed arterial segments with different stenosis severities simulated under rest and hyperemic conditions. An excellent agreement was achieved for FFR values computed from full transient simulations with the ones obtained from steady state simulation (error < 0.2 % was obtained for all test cases). The computational cost for the mean condition scenario was 0.1 that of a full transient simulation. The robustness of the method was tested by varying inflow conditions and reporting their effect on FFR. Interestingly, the predicted ischemia level was not altered when the inlet pressure was increased by 10 % from the base case. An analytical model was derived to explain the FFR independency of patient in-vivo coronary pressure. These promising findings from the numerical tests performed on idealized healthy and stenosed arterial models could significantly impact the applicability of the developed methodology and translating it into future practical clinical applications.

Commentary by Dr. Valentin Fuster
2015;():V003T03A025. doi:10.1115/IMECE2015-51589.

Spherical indentation testing is studied to evaluate the viscoelasticity of soft materials like human body. Here, the Hertzian contact theory is functionally extended to evaluate indentations for the thin tissues. In the expansions, the technique used for evaluating the thickness of finite specimens is first explained by analyzing the experimental results of indentations. Then, the viscoelasticity of soft materials with finite thickness is theoretically derived by defining an equivalent indentation strain for the analysis of the indentation process. The expansions are examined to evaluate its reliability by applying them to measure the viscoelasticity of some soft materials. Furthermore, this technology is applied to the elasticity investigation of the human body. Especially, the measurement results of viscoelastic characteristics of the body of human body are shown and the availability of developed device is discussed to reveal the deformation mechanics of human body in this report.

Topics: Elasticity
Commentary by Dr. Valentin Fuster
2015;():V003T03A026. doi:10.1115/IMECE2015-51707.

Pneumothorax is a moderately common condition in the respiratory system, which can result in significant impairment or even death. Prompt treatment is urgent for sustaining quality of life. One contributing factor when there is a delay in the administration of treatment is a lack of training for the medical staff, especially active hands-on training. This insufficient training may delay recognition and diagnosis of pneumothorax, and also delay the start of the treatment. An improved training method would potentially enable a wider range of medical staff to be ready to identify pneumothorax and administer treatment in an efficient manner.

The purpose of this project was to develop a hands on automated system for training. The system was based on a commercially available manual simulator with a hand pump. Automation was incorporated for filling of the air bag which simulated the trapped air of pneumothorax. Visual indications were presented to the user to show what state of training the simulator was in. This automated system reduced the fatigue factor, and improved the efficiency of the simulator for training trials by 60%. The automated system allowed for more trials to be performed in a given amount of time, with feedback given to the user so the trainee could be assured they were performing the treatment procedure correctly.

Commentary by Dr. Valentin Fuster
2015;():V003T03A027. doi:10.1115/IMECE2015-51836.

Bone grafts are widely used in skeletal reconstruction subsequent to tumor surgery, traumatic injuries, or in conjunction with a total joint procedure. As the graft site may be subjected to destabilizing mechanical forces, any motion at the interface between graft and the host tissue may impede or prevent healing. The application and the maintenance of the compression between screw threads and the bone is the most important factor in attaining rigid internal fixation by means of screws or screws & plates. This study is designed to assess various allograft fixation options with the intent of finding an option that is secure yet does minimal damage to the allograft. Utilizing computational modeling and analysis (SolidWorks), we compared the bending stiffness for diaphyseal bone constructs with a gap and stabilized with a dynamic compression plate, with screws placed in a unicortical or bicortical manner, with and without intramedullary PMMA. The model was validated by comparing the simulation results with the experimental results from literature for two unicortical screws application with PMMA in bending test. The study was then exteneded by looking at the stress distribution across the plates with the use of bicortical and unicortical screws with and without PMMA. For unicortical screws the use of PMMA reduces the displacement by 4:65% and reduces the stress by 5:69%. For bicortical screws, the use of PMMA reduces the displacement by 1:78% and reduces the stress by 9:45%. The bicortical screws with PMMA has a displacement which is 0:74% smaller but a stress which is 0:73% higher when compared to the unicortical screws with PMMA. From the results of total displacement and maximum stress on the plate, conclusion can be drawn that the two best arrangements are the use of unicortical screws with PMMA and bicortical screws with PMMA, thus allowing the use of fewer screws.

Commentary by Dr. Valentin Fuster
2015;():V003T03A028. doi:10.1115/IMECE2015-51872.

The lamellar or Haversian system is comprised mainly of fundamental units “osteons”. Haversian canals run through the center of the osteons where one or more blood vessels are located. The bone matrix is comprised of concentric lamellae surrounding Haversian canals. Those lamellae are punctuated by holes called lacunae, which are connected to each other through the canaliculi supplying nutrients. Haversian canals, lacunae and canaliculi of the Haversian system constitute the main porosities in cortical bone, thus it is advantageous to segregate those systems in segmented images that will help medical image analysis in accounting for porosities.

To the authors’ best knowledge, no work has been published on segregating Haversian systems with its 3 predominant components (Haversian canals, lacunae, and canaliculi) via automated image segmentation of optical microscope images. This paper aims to detect individual osteonal Haversian system via optical microscope image segmentation. Automation is assured via artificial intelligence; specifically neural networks are used to procure an automated image segmentation methodology.

Biopsies are taken from cortical bone cut at mid-diaphysis femur from bovine cows (which age is about 2 year-old). Specimens followed a pathological procedure (fixation, decalcification, and staining using H&E staining treatment) in order to get slides ready for optical imaging. Optical images at 20X magnification are captured using SC30 digital microscope camera of BX-41M LED optical Olympus microscope. In order to get the targeted segmented images, utilized was an image segmentation methodology developed previously by the authors. This methodology named “PCNN-PSO-AT” combines pulse coupled neural networks to particle swarm optimization and adaptive thresholding, yielding segmented images quality. Segmentation is occurred based on a geometrical attribute namely orientation used as the fitness function for the PSO. The fitness function is built in such way to maximize the identified number of features (which are the 3 components of the osteonal system) having same orientation.

The segmentation methodology is applied on several test images. Results were compared to manually segmented images using suitable quality metrics widely used for image segmentation evaluation namely precision rate, sensitivity, specificity, accuracy and dice.

The main goal of segmentation algorithms is to capture as accurate as possible structures of interest, herein Haversian (osteonal) system. High quality segmented images obtained as well as high values of quality metrics (approaching unity) prove the robustness of the segmentation methodology in reaching high fidelity segments of the Haversian system.

Commentary by Dr. Valentin Fuster
2015;():V003T03A029. doi:10.1115/IMECE2015-51993.

Cardiovascular disease is one of the leading causes of death in the world, accounting for 30% of all deaths worldwide and 40% of those occurring in New Zealand. In recent years, engineers and scientists have collaborated with the medical community to find new methodologies and approaches for assessing, investigating and understanding the development of cardiovascular diseases. Elements such as computational models developed with fluid dynamic elements (CFD/FE) have become excellent tools for this purpose. One of the important approaches is developing devices for investigating the central blood flow and pressure, and correlating the results to different heart diseases. Higher-valued changes in central blood flow and pressure mean that the heart must work harder. A computational model capable of predicting inlet and outlet locations of a blockage would be helpful to determine different stages of cardiovascular disease. By using reflection signals from the central blood flow that are detected at locations such as the brachial artery or subclavian artery, it is possible to model the effect of flow and pressure differences on heart diseases.

Commentary by Dr. Valentin Fuster
2015;():V003T03A030. doi:10.1115/IMECE2015-52086.

Microfluidic devices are widely used in biomedical applications owing to their inherent advantages. Microfabrication techniques are common methods for fabricating microfluidic devices, which require specialized equipment. This paper presents a multi-layer construction process for producing microfluidic devices via integrating two accessible fabrication techniques — hydrogel molding, a microfabrication-free method, and electrospinning (ES). The formed microchannels were examined via analyzing micrographs. Preliminary results demonstrate the feasibility of the method and potential for incorporating complex channels and device optimization.

Commentary by Dr. Valentin Fuster
2015;():V003T03A031. doi:10.1115/IMECE2015-52146.

Cardiovascular stents are currently being used for intraluminal stenting of the trachea for tracheomalacia treatment. These devices composed of permanent materials are controversial due to their limitations at internal reinforcement and biocompatibility, especially in pediatrics. We show in a pediatric tracheomalacia rabbit model, a poly-L-lactic acid (PLLA) Double Opposed Helical bioresorbable stent (DH) elicits a more mild inflammatory response in the malacic airway compared to a control metal stent. To further improve efficacy, a multi-drug delivery, bioresorbable coating was designed. The coating design controllably delivers ciprofloxacin (antibiotic) for one week and dexamethasone (anti-inflammatory agent) for three months. The bioresorbable polymeric components also demonstrate feasible visibility utilizing Magnetic Resonance Imaging (MRI). The local multi-drug delivery and imaging capabilities in this coating design in combination with the bioresorbable DH stent will result in a successful intervention specifically design for pediatric tracheomalacia. This design will eliminate long-term risks associated with current permanent devices and provide necessary theranostic agents to facilitate healing and monitor progress via non-invasive imaging techniques.

Commentary by Dr. Valentin Fuster
2015;():V003T03A032. doi:10.1115/IMECE2015-52370.

Knowledge of positional and force properties of surgical dissection in neurosurgery is essential in developing simulation platforms for neurosurgical training such that realistic motion and perception can be conveyed to the trainee during practice. Most proposed models in literature utilize computational techniques to formulate required parameters. However, these models are not realistic enough compared to data obtained from experiments on real brain. Therefore, developing a setup to measure the position, orientation, and interaction forces will help researchers formulate realistic parameters. This paper presents the development of such a setup for quantification of displacements and tool-tissue interaction forces during performance of microsurgical tasks. A bipolar forceps is equipped with a set of force sensing elements to measure the tool-tissue interaction force components. The position and orientation of the forceps tips are measured by attaching a tracker to the bipolar forceps. To show proof-of-concept, an experienced surgeon and one assistant surgeon performed 35 neurosurgical tasks (320 trials) on a cadaver brain (previously-frozen) using the instrumented setup. Positional and force data of the bipolar forceps were recorded during surgical dissection of different brain structures. This paper reports results collected from two microsurgical tasks over 40 trials: dissection of sylvian cistern arachnoid (SCA) and dissection of middle cerebral artery (MCA). Results showed that the mean values of interaction forces during dissection of MCA were smaller than dissecting SCA. The maximum forces observed were 1.94 N and 1.75 N for SCA and MCA, respectively. The application of quantifying such parameters using the developed setup will be in training neurosurgery residents using surgical simulators in which the knowledge of brain tissue parameters is required to formulate the tissue model.

Topics: Surgery , Displacement
Commentary by Dr. Valentin Fuster
2015;():V003T03A033. doi:10.1115/IMECE2015-53499.

Pelvic floor disorders such as Pelvic Organ Prolapse (POP) negatively impact the health and quality of life of millions of women worldwide. POP is characterized by the descent of the pelvic organs into the vagina due to compromised connective tissue support, resulting in discomfort and urinary/fecal incontinence. Magnetic Resonance Imaging (MRI) has been used to aid in the quantification of these anatomical changes, however the inter- and intra-observer repeatability necessary to make reliable conclusions about changes in anatomical positioning is questioned using current methods. The aim of this study was to quantify the degree of variability produced from inter-observer manual tracings of the vagina from MRI scans using a statistical shape matching approach.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Computational Modeling and Device Design

2015;():V003T03A034. doi:10.1115/IMECE2015-50481.

Cancer is one of the most dangerous diseases widespread around the world. Developing the most efficient cures for cancer strongly relies on a comprehensive understanding of cancer cells. Circulating Tumor Cells (CTCs) are cancer cells detached from the primary tumor site and released into the blood. CTCs are the main source of cancer metastasis. Devising devices to identify and separate these cells from the blood is of great importance since these cells represent cancer in many aspects. Because of the rarity of CTCs in the blood, designing efficient CTC separation devices has become a challenging issue. Among different CTC separation devices, deformability-based CTC separation devices have become very popular recently because of their simplicity and their relatively low cost. In this research, we investigate numerically the deformability-based CTC separation microfilters. Specifically, we study non-uniform cross-sectional microfilters because of their ability in unclogging. Different microfilter geometries are selected for this study including conical-shaped and rectangular cross-section microfilters with different channel profiles. In this study, we mainly focus on the effect of different design parameters on system performance criteria. The main performance criteria are: critical pressure of the system, system throughput and cell clogging in filtration. Critical pressure, which is defined as the maximum pressure for a cancer cell to squeeze through the microfilter, is an important design aspect. Applying a pressure lower than the critical pressure causes the cell to get stuck in the microfilter, while applying much higher pressure on the system may result in cellular damage which has negative effect on the viability of the cell for post processing. System throughput is also of great importance. A high-throughput CTC filtration system is always more desirable in clinic applications. System clogging, which decreases the CTC separation efficiency, is one of the challenging issues in these devices. In this research, we first simulate how a cell behaves in a passing event process through the microfilter. Specifically, we focus on how different cells squeeze through the microfilter. This gives us more insight through the separation process. Second, we investigate the effect of different microfilter geometries on the critical pressure required for separation of cancer cells. Third, the effect of applied inlet pressure on the system performance is studied. Our results indicate that the critical pressure varies significantly with microfilter geometry. Results also show that the device throughput is strongly related to the applied pressure. Moreover, the filtration simulation demonstrates that system clogging occurs if unsuitable pressure is applied on the system.

Commentary by Dr. Valentin Fuster
2015;():V003T03A035. doi:10.1115/IMECE2015-50693.

The tibia diaphysis (shaft) fracture is one of the most common long bone fractures, and is usually treated with either the internal or the external fixations. How to choose a proper fixation type is still empirical and controversial. The objective of this study was to investigate whether the lateral external fixation (LEF) is suitable to treat the transverse and oblique tibia diaphysis fracture, from a mechanobiological perspective. The healing processes in the tibia fractures were simulated using the finite element method. The models of both the transverse and oblique (45°) tibia diaphysis fracture fixed with a LEF were built. A mechano-bioregulatory algorithm, which considered both the mechanobiological and biological environments, was developed to simulate the cell and tissue activities inside the callus. The results showed that both fractures healed in a typical secondary osteogenesis process. After 60 days, the regions of external callus and bone marrow were occupied with bone tissue. However, the mechanical stimulus in the inter-cortical region in the oblique fracture model with a less stiff LEF was greater than the stimulus in the transverse fracture model with the same LEF, indicating that the angled fracture was prone to generate greater instability. Moreover, increased osteogenic differentiation threshold only slightly affected the bone formation in the bridging areas, thus, had minor influences on the healing process. In conclusion, the lateral external fixation demonstrated satisfactory capacity in the treatment of the transverse and oblique tibia diaphysis fracture. The oblique fracture was more likely to be affected with a less stiff fixation.

Commentary by Dr. Valentin Fuster
2015;():V003T03A036. doi:10.1115/IMECE2015-50838.

Mechanical ventilation is the process of providing artificial breathing support to a patient. More than half of critically ill patients require mechanical ventilation[1]. Though mechanical ventilation increases time for recuperation, it is known to have given rise to complications arising from over-distention of lungs leading to ventilator associated lung injury (VALI) and ventilator induced lung injury (VILI). This paper aims to develop a sensor to identify breathing efforts initiated by the patient and give back responses to the ventilator to regulate ventilation modes and tidal volumes delivered by the ventilator. This will significantly aid in reducing asynchrony between the patient efforts and the ventilator input, thus preventing lung injury. Towards this end, we have simulated and studied the effect of different kinds of dynamic loading and diaphragm membrane thickness of the sensor on its sensitivity on a basic design.

Commentary by Dr. Valentin Fuster
2015;():V003T03A037. doi:10.1115/IMECE2015-50926.

A low cost continuous passive motion (CPM) machine, the Gannon Exoskeleton for Arm Rehabilitation (GEAR), was designed. The focus of the machine is on the rehabilitation of primary functional movements of the arm. The device developed integrates two mechanisms consisting of a four-bar linkage and a sliding rod prismatic joint mechanism that can be mounted to a normal chair. When seated, the patient is connected to the device via a padded cuff strapped on the elbow. A set of springs have been used to maintain the system stability and help the lifting of the arm.

In this work a multi-body simulation was performed with the software SimWise 4D by Design Simulation Technologies (DST). The simulation was used to determine the stiffness of the springs in the mechanism to provide assistance to raising of the patient’s arm. Furthermore, the software can provide a finite element analysis of the stress induced by the springs on the mechanism and the external load of the arm. Finally, a physical prototype of the mechanism was fabricated using PVC pipes and commercial metal springs. Due to the low cost of fabrication, simplicity, and ease of adjustability, it is believed that the GEAR has the potential to provide effective passive movement to individuals who otherwise would not have access to post-operative or post-stroke rehabilitation therapy.

Commentary by Dr. Valentin Fuster
2015;():V003T03A038. doi:10.1115/IMECE2015-50929.

An anterior cruciate ligament (ACL) tear is one of the most prominent, and debilitating injuries currently to athletes. Physical therapist students need to be able to practice common physical examination techniques regularly and repeatedly in order to gain the skills necessary to accurately diagnose an ACL tear. A cost effective, adjustable knee apparatus that could mimic the behavior of both a healthy and an injured knee joint may mitigate this problem. We built an apparatus mimicking the geometry and function of a knee joint, including the effect of forces and stiffness proper of knee ligaments. SimWise 4D was used to dynamically simulate an anatomically approximated model of the knee joint during physical examination conditions. The numerical simulation tested the displacement between the femur and the tibia with and without an ACL ligament. The SimWise 4D simulation gave an increase in displacement of 1.58 mm or 30% after removing the ACL, which is comparable with known displacements in human test subjects. Finally, a design for a 3D rapid prototype is proposed and fabricated with fusion deposition modeling (FDM).

Commentary by Dr. Valentin Fuster
2015;():V003T03A039. doi:10.1115/IMECE2015-51072.

The main purpose of this research is to analyze blood flow in various scenarios such as 20%, 50% and 80% blockage in blood vessel due to aortic atherosclerosis. Valuable Information for clinical diagnosis of cardiovascular diseases can be obtained by analyzing the behavior of blood flow and its variations. An idealized numerical model of the human bifurcated aorta is created then simulations of steady blood flow were performed on this model and various parameters have been considered. The model parameters include the blood flow velocity, pressure, wall shear stress (WSS) of vessels, constant blood density and constant viscosity. The data computed from software indicates behavior of blood flow according to changes in physical properties of blood vessel. These results are mostly similar to physiological and pathological results of vessels observed in clinical practice. This study will eventually help to find the Fluid Structure Interaction (FSI) of blood flow and blood vessel which will be bring a favorable change in cardiovascular diseases treatments.

Commentary by Dr. Valentin Fuster
2015;():V003T03A040. doi:10.1115/IMECE2015-51075.

The purpose of this paper is, to provide the non-linear biodynamic response of thorax through the analytical and numerical simulation methods. Adult thorax data considering sagittal and coronal stiffness in addition to soft and hard tissue material properties will undergo CPR impulsive loading. The numerical simulation is conducted using finite element analysis (FEA) software for modeling biomechanical correct Thorax model to CPR transient loading. AMTI force plate was utilized to record the CPR forces, it accounts for realistic load evaluation during CPR procedure. A dynamic model for numerical simulation includes resonance frequency, damping coefficient, stiffness constant and extinction time for a different kind of physique. The model deflections and forces were analyzed. The maximum deflection obtained from mathematical modelling and ANSYS is found closely related. The result strongly depends on the modeling of the thorax which is used in the numerical simulation. This indicates the necessity of the correlation of the results with the experimental data if available.

Commentary by Dr. Valentin Fuster
2015;():V003T03A041. doi:10.1115/IMECE2015-51515.

Myopia or shortsightedness is a visual impairment condition that is affecting more than 32 million Americans according to the American Academy of Ophthalmology, and this number is expected to increase even further with the increasing life expectancy in the United States. Myopia occurs when light rays entering the cornea are focused in front of the retina due to: high corneal curvature, short axial length of the eye, or high optical power of the natural lens. These reasons suggest that light refracting elements play a pivotal role in determining visual acuity. The cornea is the principal refractive element in the eye contributing almost 75 percent of ocular refractive power and if the shape of the cornea can be changed to increase or decrease the focal length of the converging light rays it could present a possible solution to improving myopia. The presented research focuses on the effects of intrastromal corneal ring (ICR) implantation on the shape of the cornea by developing a computationally efficient 3D axisymmetric finite element (FE) model of the cornea utilizing hyperelastic material properties. The results of the developed corneal FE model with a 360° ICR implant are analyzed and discussed. The FE model results provide confidence in the ability of the ICR implants to reduce myopia. The attained FE model results not only agree qualitatively with published clinical data but also provide a valuable insight into the surgery.

Commentary by Dr. Valentin Fuster
2015;():V003T03A042. doi:10.1115/IMECE2015-51576.

Most modern active prostheses try to match the torque generated by the biological ankle in order to assist walking. However, due to the absence of a biarticular component like the gastrocnemius muscle, they are unable to provide complete rehabilitation. In this paper, a conceptual design of a prosthesis, having an active biarticular component is proposed; and it is studied if such a design can help in better rehabilitation of amputees. The muscle and joint forces during walking are predicted for three cases using musculoskeletal models: A healthy person, an Amputee wearing an active uniarticular prosthesis, and an Amputee wearing a prosthesis having active uniarticular as well as biarticular components (proposed design).

Based on the required muscle forces and generated joint reaction loads, the proposed model performs better than the uniarticular prostheses.

Commentary by Dr. Valentin Fuster
2015;():V003T03A043. doi:10.1115/IMECE2015-51688.

Bruxism is a nonfunctional motor activity that is characterized by grinding and clenching of the teeth. It has been postulated that bruxism causes excessive occlusal load on the dental implant and its superstructures leading to biological and biomechanical complications. While many researchers suggest that grinding/clenching causes early implant complications and accelerated bone loss, others indicate that the long term effects are still unclear. The goal of this study is to analyze the effect of bruxism loading condition on the stress distribution of an implant supported overdenture (ISO) using finite element analysis (FEA) and compare the results with one of the most functionally efficient occlusion schemes in the clinical dentistry — lingualized occlusion. A high fidelity solid model of a mandibular denture encompassing lingual and buccal cusps, mesial and distal fossae supported by four implants and a connecting titanium prosthetic bar, resting on alveolar bone were modeled in SolidWorks 2013 following proper clinical guidelines and imported to ANSYS 15.0 for stress analysis. The results of the study demonstrate that the stress distribution in the implant prostheses and surrounding bone is significantly affected due to bruxism as compared to the lingualized loading. While the location of the maximum stress concentration was the same (neck of the posterior implants) for both loading conditions, there was an increase of approximately 115% von-Mises stress for bruxism loading condition as compared to the lingualized occlusion. The maximum principal stress in the cortical bone surpassed the ultimate tensile strength limit of the jaw bone implying possibility of bone resorption in the peri-implant area.

Commentary by Dr. Valentin Fuster
2015;():V003T03A044. doi:10.1115/IMECE2015-51718.

The controlled cortical impact (CCI) model is commonly used for replicating the trauma events. However, the impact parameters vary considerably among different laboratories, making the comparison of research findings difficult. The goal of this work is to quantify the intracranial pressure responses to the input parameters of the CCI device using a surrogate head, i.e., a gel-filled ping pong ball. Findings from this work could be used to better design CCI tests.

Topics: Pressure
Commentary by Dr. Valentin Fuster
2015;():V003T03A045. doi:10.1115/IMECE2015-51765.

The most widely accepted hypothesis to explain normal pressure hydrocephalus (NPH) points at the increase of cerebrospinal fluid (CSF) outflow resistance as the fundamental cause. Some clinical and experimental studies do not agree with this hypothesis and suggest that NPH is related to an alteration of the CSF pulse pressure waveform, while intracranial pressure (ICP) mean value has negligible effects.

The current treatment of hydrocephalus is based on the first hypothesis and consists in the implantation of CSF shunts. An improved treatment can be obtained by damping the ICP pressure peaks and keeping unchanged the mean value.

The target of this work is to design a special ICP regulator valve, that will be implanted in a human body and that must be characterized by a purely mechanical working principle avoiding any electrical equipment (sensors, actuators...).

This device is currently patented [1] and in virtue of that the paper will focus only on the general device working principle and design methodology rather than specific data.

Since the device must be implanted inside the patient head, the system must satisfy very restrictive requirements: low weight and dimensions in order to avoid possible patient discomfort or obstacles to the normal life activities, in addition, being the valve application place close to a delicate organ such the brain is, the mechanism must be very simple and must reach very high reliability standards (almost zero maintenance and possible failures).

The idea is to realize a device in which the hydraulic flow is governed by a spring with variable stiffness with respect to the applied loads (intracranial pressure: characterized by both a mean constant component and by random oscillatory phenomenon).

To maximize the valve effect about pressure peaks reduction, the spring will be designed with a strongly non-linear behavior characterized by bistable working principle.

The systems that show this properties are innumerable, but according to the author hypothesis to realize a mechanism as simpler as possible the choice done falls into the thin curved plate (shell) category.

In particular, the goal is to obtain a plate behavior called “Buckling Behavior”: under determined load conditions the plate geometric configuration must suddenly switch from an equilibrium position to another. The two target parameters which describe this phenomenon are the buckling critical load that is the applied load value for which the plate change the geometric configuration (valve activation point) and the load application point displacement (evacuation pipe opening).

The adopted design method is the non-linear analysis developed in a finite element analysis (F.E.A.) environment, by which it is possible to analyze a component behavior also in case of large displacements.

To identify the optimal component geometry the load application point displacement versus the acting load was evaluated as function of the main parameters describing the plate profile: plate semi-length, curvature radius and semi-length of the plate plane portion.

This work represents only a preliminary study oriented to demonstrate the feasibility in realizing a biomedical valve for fluids pressure control, adopting a thin curved plate with “Buckling Behavior”. Moreover it provides useful information for the designer who wants to realize curved plate with buckling behavior showing the influence of the main geometric parameters on this phenomenon.

Further in depth studies oriented to: the spring stiffness regulation for different patients, best material choice and productive process must be accomplished before the device realization.

Topics: Design , Biomedicine
Commentary by Dr. Valentin Fuster
2015;():V003T03A046. doi:10.1115/IMECE2015-51845.

The patch material and dimension are two important factors which might affect the surgical outcomes after the aortic arch coarctation repair surgery. To quantity their acute impacts on the biomechanical environment of the repaired aortic arch, an aortic arch model was constructed and the fluid-structure interaction (FSI) technique was utilized to characterize its hemodynamics and wall mechanics. Three different patch materials were considered including pulmonary artery, ECM CorMatrix and Polytetrafluoroethylene (PTFE). The induced wall shear stress, distribution of flow patterns, and von-Mises stress on arterial wall were compared. Results showed that ECM CorMatrix patch had better performance Two different patch dimension (large v.s small) using CorMatrix patch were compared and the relatively smaller patch demonstrated a better hemodynamics than the larger one. No significant difference in terms of wall stress was observed between the different patch sizes.

Commentary by Dr. Valentin Fuster
2015;():V003T03A047. doi:10.1115/IMECE2015-52078.

Abdominal Aorta Aneurysm (AAA) affects aorta, especially above the iliac bifurcation where the Wall Shear Stress (WSS) is greater. Consequence may be fatal in case of breakage; a way to treat it is Endovascular Aneurysm Repair (EVAR) where a stent graft is placed inside the aorta without open surgery requirement. Because of the standards, stent graft can be chosen between several sizes: in some cases, this device cannot fit perfectly with the anatomy of the patient and this can lead to a not optimal behavior of the prosthesis and further complications.

This study present a method to design and test specific custom-fit stent graft able to better adapt to the patient artery improving the efficiency of the prosthesis and reducing the risk of the migration of the graft as well as the fabric torn. The design method is based on a 3D geometric model of the aorta, generated from CT scan data. Centrelines and geometric data for cross sections along the aorta are the inputs necessary to define the mesh of the stent. A custom algorithm is developed to size the stent in relation to the geometric data of the specific patient; when the frame of the prosthesis is defined, a CAD-based Loft Surface has used to define surfaces between the stent rings. For the bifurcation, again CAD-based Boundary Surfaces is used.

The described procedure has been also applied in a Augmented Virtual Reality simulation of the EVAR and, finally, it permits a CFD simulation to evaluate the behavior of the prosthesis inserted into the aorta.

Topics: Design , stents
Commentary by Dr. Valentin Fuster
2015;():V003T03A048. doi:10.1115/IMECE2015-52123.

The effect of gravity is considered on biomechanical modeling of human lung deformation for radiotherapy application. The lung is assumed to behave as a poro-elastic medium with spatially dependent property. Finite element simulation is performed on a three-dimensional (3D) lung geometry reconstructed from four-dimensional computed tomography (4DCT) scan dataset of real human patient. The spatially-dependent Young’s modulus (YM) values are estimated using inverse analysis from a linear elastic deformation model. First, the gravity-generated deformation in the lung is calculated. Next, inlet pressure loading is applied at the hilium from an initial stress-free resting volume. Then, the lung model is preloaded by its weight, followed by prescription of the inlet pressure. In each case the maximum and minimum deformation of selected landmarks are monitored with and without gravity. The results show that gravity indeed significantly affects the magnitude and distribution of lung deformation. The maximum displacement increases by 54% in the direction of gravity when it is considered in the model.

Commentary by Dr. Valentin Fuster
2015;():V003T03A049. doi:10.1115/IMECE2015-52265.

This study compares the effects of lingualized and linear occlusion schemes on the stress distribution of an implant retained mandibular overdenture (IRO) using finite element analysis (FEA). A high fidelity solid model of mandibular overdenture incorporating cusps and fossae of occlusal surface with two anterior implants in the canine regions and residual ridge support in the posterior region of the alveolar bone was modeled in SolidWorks and imported to ANSYS for stress analysis. The load was applied vertically to the central grooves and buccal cusp tips of the premolars and molar teeth for the lingualized and linear occlusion respectively. The loading magnitudes were 200 N on the premolars and 200 N on the molar teeth with multiple contact locations. The results show that the linear occlusion scheme generated higher stress in the implants and the prosthetic bar than the lingualized occlusion. The locations of high stress concentrations were the neck of the implants and the implant-prosthetic bar intersection for both the occlusion schemes. However, in the cortical bone lingualized occlusion loading scheme generated higher stress (max principal stress) than the linear one suggesting possibility of greater bone loss. The results of this study could be used to comprehend the stress distribution in the denture teeth, base, bone-implant interface and surrounding bone for the two occlusion concepts and may be of help to the clinicians in choosing the right scheme for the edentulous patients.

Commentary by Dr. Valentin Fuster
2015;():V003T03A050. doi:10.1115/IMECE2015-52638.

Stent thrombosis is a major complication that occurs after the placement of stents in the coronary artery through balloon angioplasty. The common treatment for stent thrombosis is to provide patients with anticoagulant and antiplatelet therapy through the bloodstream. This study uses numerical modeling to compare two delivery methods of heparin anticoagulant to the arterial wall to reduce thrombus formation: through the flow and via a drug-eluting stent. A unique computational fluid dynamics model is developed that couples an incompressible flow solver with a convection-diffusion-reaction equation solver. The flow solver uses a sharp-interface immersed boundary method on a Cartesian grid to characterize pulsatile flow over the curved wires of the stent. Concurrently, the convection-diffusion-reaction equations are solved for the 19 coupled reactions that make up the coagulation cascade and heparin interactions, as well as reaction and transport equations for both active and inactive platelet species. The simulation is run with input boundary conditions of steady flow, pulsatile Poiseuille flow, and a Womersley flow profile. Results are collected for the bare metal stent case, anticoagulant delivered through the bloodstream, and anticoagulant delivered through a drug-eluting stent. The results generally find that the drug-eluting stent delivery of anticoagulant is more effective in reducing platelet activation and clotting, while also providing a more localized anticoagulant distribution.

Commentary by Dr. Valentin Fuster
2015;():V003T03A051. doi:10.1115/IMECE2015-52734.

The ability to incorporate three-dimensional (3D) hepatocyte-laden hydrogel constructs using layered fabrication approaches into devices that can be perfused with drugs enables the creation of dynamic microorgan devices (DMDs) that offer an optimal analog of the in vivo liver metabolism scenario. The dynamic nature of such in vitro metabolism models demands reliable numerical tools to determine the optimum process, material, and geometric parameters for the most effective metabolic conversion of the perfused drug into the liver microenvironment. However, there is a current lack of literature that integrates computational approaches to guide the optimum design of such devices. The groundwork of the present numerical study has been laid by our previous study [1], where the authors modeled in 2D an in vitro DMD of arbitrary dimensions and identified the modeling challenges towards meaningful results. These constructs are hosted in the chamber of the microfluidic device serving as walls of the microfluidic array of channels through which a fluorescent drug substrate is perfused into the microfluidic printed channel walls at a specified volumetric flow rate assuring Stokes flow conditions (Re<<1). Due to the porous nature of the hydrogel walls, a metabolized drug product is collected at the outlet port. A rigorous FEM based modeling approach is presented for a single channel parallel model geometry (1 free flow channel with 2 porous walls), where the hydrodynamics, mass transfer and pharmacokinetics equations are solved numerically in order to yield the drug metabolite concentration profile at the DMD outlet. The fluid induces shear stresses are assessed both in 3D, with only 27 cells modeled as single compartment voids, where all of the enzymatic reactions are assumed to take place. In this way, the mechanotransduction effect that alters the hepatocyte metabolic activity is assessed for a small scale model. This approach overcomes the numerical limitations imposed by the cell density (∼1012 cells/m3) of the large scale DMD device. In addition, a compartmentalization technique is proposed in order to assess the metabolism process at the subcellular level. The numerical results are validated with experiments to reveal the robustness of the proposed modeling approach and the necessity of scaling the numerical results by preserving dynamic and biochemical similarity between the small and large scale model.

Commentary by Dr. Valentin Fuster
2015;():V003T03A052. doi:10.1115/IMECE2015-53014.

Traumatic brain injury (TBI) has been recognized as the signature wound of the current conflicts and it has been hypothesized that blast overpressure can contribute a significant pathway to TBI. As such, there are many ongoing research efforts to understand the mechanism to blast induced TBI, which all require blast testing using physical and biological surrogates either in the field or in the laboratory. The use of shock tubes to generate blast-like pressure waves in a laboratory can effectively produce the large amounts of data needed for research into blast induced TBI. A combined analytical, computational, and experimental approach was developed to design an advanced shock tube capable of generating high quality out-of-tube blast waves. The selected tube design was fabricated and laboratory tests at various blast wave levels were conducted. Comparisons of tube-generated laboratory data with explosive-generated field data indicated that the shock tube could accurately reproduce blast wave loading on test surrogates. High fidelity blast wave simulation in the laboratory presents an avenue to rapidly and inexpensively generate the large volumes of data necessary to validate and develop theories linking blast exposure to TBI.

Commentary by Dr. Valentin Fuster
2015;():V003T03A053. doi:10.1115/IMECE2015-53525.

This work focuses on the biomechanical simulation of surgery for total replacement of the first metatarsophalangeal joint (MTPJ) allowed us to identify and analyze several key aspects for finite element simulation of hallux rigidus pathology. Predicting the optimal response of a finite element model (FEM) depends on proper characterization. At this part of the work, those conditions that have a direct or indirect influence on the model that can change its behavior should be considered.

For this purpose, we presented in this work a finite element model which include 26 bones: 14 phalanges, 5 metatarsals, 3 cuneiform bones, 1 cuboid, 1 navicular, 1 talus and 1 calcaneus, all of them include articular cartilage. In addition, the model also considers: thin ligaments, long ligaments, muscles and a joint implant.

Loads and boundary conditions included: a pretension in the flexor caused by position analysis, a distributed load in the talus in its normal and tangential component, a restriction of movement of some points in the phalanges and calcaneus and the contact conditions between flexor and extensor created from surfaces in the bone volumes.

Moreover, the selection of support and constrains regions in the phalanges and calcaneus area must be carefully selected to reproduce the conditions of real support and interaction with adjacent tissues not simulated. These conditions have influence in the structural biomechanical response of each tissue and in contact regions, leading to unexpected behavior if they are wrong selected. In addition, results showed that care must be taken in the mechanical characterization of each tissue, selecting the mechanical properties, pretension, geometry and critical position according to in vitro results or MRIs.

Biomechanical aspects reported in this work allow to take into account fundamental details to improve future simulations of this pathology as well as to improve the correlation with experimental results. These biomechanical aspects provide knowledge for finite element simulation of the arthroplasty for the first metatarsophalangeal joint, this allow us to generate a virtual model for arthroplasty of the hallux rigidus to predict, prevent and improve surgical techniques for implantation of prostheses in the first metatarsophalangeal joint.

Commentary by Dr. Valentin Fuster
2015;():V003T03A054. doi:10.1115/IMECE2015-53568.

Centrifugal blood pumps have to be considered from both mechanical and biomechanical aspects. While, evaluations of mechanical factors, such as performance curve, are straightforward, biomechanical parameters, such as hemolysis indices, are still indistinct. Hence, different mathematical models and computational methods have been employed for the evaluation of hemolysis indices. This article aims to investigate four different types of centrifugal blood pumps from both mechanical and biomechanical aspects. The pumps are cone-type impeller (Type-A), channel-type impeller with shroud (Type-B), open impeller without shroud (Type-C) and shrouded impeller-type (Type-D). The CFD simulations are conducted using standard k-ε turbulence model in multiple reference frame (MRF) method. Various values for rotational speed and flow rate are studied. The streamlines clearly show the effects of impeller geometry on flow patterns. It is also demonstrated that in all of the models, the areas of the recirculation have high value of von Mises stress. In addition, the effect of the volute in the Type-D on the pressure distribution and streamline smoothness is clearly observed. In another part, the modified index of hemolysis (MIH) calculated based on Eulerian approach is investigated for three predefined conditions of extracorporeal membrane oxygenation (ECMO), ventricular assist device (VAD), and full-load. The results reveal that the Type-A and Type-D have the highest and lowest MIH values, respectively in all of the predefined conditions. In addition, all of the pumps generate lower amount of hemolysis when they are operated in VAD condition.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Damage Biomechanics

2015;():V003T03A055. doi:10.1115/IMECE2015-50639.

Skeletal trauma occurs in many blunt, ballistic and blast impact events. Even though the personal body armors and protective equipment were effective in stopping the penetration of bullets or fragments, the resulting impact loading could lead to the significant injuries and fractures to the thoracic skeleton and extremities. The finite element (FEM) method, with its capability to handle complex geometries and nonlinear materials, are commonly used to analyze the tissue biomechanical responses and correlate the simulation results with the injury outcomes. However, it is very difficult to construct the three-dimensional (3D) FEM model for the skeletal biomechanics analysis because of the complex geometry and different materials involved. Moreover the simulation of 3D FEM model is computationally expensive because both small element size and high speed of sound in materials lead to very small time step in an explicit transient analysis. The simulation process is often not robust enough when the model experiences the large deformation. To shorten modeling and simulation times, we have developed a fast running model based on a novel nonlinear beam element for the skeletal impact biomechanics analysis. In contrast to the conventional beam elements, the kinematics of the developed beam element is free of rotational degrees of freedom (DOFs). The current beam element offers the desired constant lumped mass matrix for the large deformable explicit transient analysis. The realistic treatment of junctions and surface intersections among beams becomes straightforward. Furthermore the model can account for the irregular shape and different materials at beam cross sections by using the numerical integration. The sophisticated material models such as elastoplasticity can also be incorporated directly in the integration points. Thus the fast running model is suitable for the analysis of complex nonlinear composite structures such as the loading-carrying thoracic skeleton and extremities. The stereolithograph (STL)-based anatomical geometry of skeletal structure is used to extract the one-dimensional (1D) curved beam model and the associated beam cross sections. The anatomical surface of skeleton is also utilized for the calculation of transferred loads to the underlined beams. The 3D responses such as displacements and stresses from the fast running model are subsequently reconstructed on the anatomical surface for the visualization and skeletal trauma analysis. We demonstrate the efficiency of such modeling technique by simulating the rib cage and the lower extremity under the impact loadings. As compared to the 3D FEM model, the developed model runs fast and robust, and achieves good results without the need of laborious 3D meshing process.

Topics: Biomechanics
Commentary by Dr. Valentin Fuster
2015;():V003T03A056. doi:10.1115/IMECE2015-51809.

The seatbelt is the most important safety device that saves the life during vehicle collisions. The majority of vehicles available today are equipped with the conventional single loop three-point belt systems. In this belt system for the front outboard positions, the shoulder anchor point (D-Ring) is fixed on the vehicle B-pillar. Vehicle manufacturers are required to show the compliance with established FMVSS regulations ensuring adequate safety performance of restraint system during a frontal crash scenario. This performance evaluation is based on the study of the biomechanical response of the crash dummy used. In these evaluations, the front outboard seats and respective seatbacks are set to be based on manufacturers nominal riding position that usually consist of seatback recline less than 20 deg with vertical. The conventional belt and its fit around the occupant are the function of seatback recline angle. The belt fit get worse with higher seatback recline angles and reduce the level of protection offered during a frontal crash scenario. In some situations, this condition also causes severe to critical injuries.

The purpose of this study was to conduct research on the effect of automotive reclined seatback in a moving vehicle on the deterioration of occupant protection and modification in the injury pattern. A real world case is investigated and presented in this paper explaining the dangers of reclined seat in moving a car with a conventional belt system. The investigation involved a detailed study of crash reports, Medical documents, medical scans, accident reconstruction, vehicle inspection, witness statements and other pertinent crash related facts. A surrogate study is conducted on a similar vehicle to identify occupant’s body configuration with respect to various interior components of the vehicle including the seatbelt webbing. The surrogate study also facilitates the understanding of interior marks generated by occupant contact during secondary impacts. A detailed injury mechanism analysis is conducted to identify the best injury prevention countermeasure in such scenario. The injured occupant sustained cervical spinal cord injury in this crash. Abdomen fat stranding analysis is conducted to conclude the lap belt submarining in the crash with reclined seatback.

An MADYMO computer modeling study is conducted to explain the occupant kinematics in this frontal crash with reclined seatback and locked hanging shoulder portion of the webbing. The analysis provides insight regarding the kinematics and body interaction with various involved physical components inside the vehicle. This model shows submarining of the pelvis under lap belt that shows occupants vulnerability for abdomen injuries along with other associated severe injuries. The altered kinematics causes occupants neck to interact with the locked shoulder portion of the seatbelt. This knowledge is extremely important for the development of the best injury prevention schemes by improving the crashworthy performance of the vehicle to prevent such injuries.

Topics: Vehicles , Wounds
Commentary by Dr. Valentin Fuster
2015;():V003T03A057. doi:10.1115/IMECE2015-51979.

Skull fracture can be a complex process involving various types of bone microstructure. Finite element analysis of the microscopic architecture in the bone allows for a controlled evaluation of the stress wave interactions, micro-crack growth, propagation and eventual coalescence of trabecular fracture. In this paper, the microstructure and mechanics of small-volume sections of a 6-month-old Gottingen Minipig skull were analyzed. MicroCT scans were used to generate finite element models. Various computational methods were investigated for modeling the intricacies contained within the porous microstructure of the trabecular bone. Pores were explicitly meshed in one method, whereas in the second, a mesh was created from a microCT image-informed mapping algorithm that mapped the trabecular porosity from an image stack to a solid volume mesh of the model. From here, all models were subject to uniaxial compression simulations. The output of the simulations allowed for a detailed understanding of the failure mechanics of the skull structure and allowed for comparison between the methods. Fracture typically occurs in the weakest areas where the bone is highly porous and forms a fracture surface throughout the material, which causes the bone to collapse upon itself.

Topics: Bone
Commentary by Dr. Valentin Fuster
2015;():V003T03A058. doi:10.1115/IMECE2015-51984.

This preliminary study aims to computationally model and study the fracture patterns in the human calcaneus during variable impact loading conditions. A finite element model of the foot and ankle is used to understand the effect of loading rates and orientation of the foot on fracture patterns. Simulations are carried out by applying varying impact velocities of steel plate to the foot & ankle model in accordance with data regarding underbody blasts. These impact velocities are applied to reach a peak in 1.5 ms. Fracture of bone is represented using the plastic kinematic constitutive model with element erosion method, where elements are removed from the simulation after an inelastic failure strain is exceeded. The simulations last for 5 ms to observe the extent of fracture in the calcaneus.

Following simulations, the resulting fracture patterns are compared to available images from experimental impact tests to qualitatively assess the simufutions. A mesh convergence study is performed to determine the level of refinement of mesh necessary to represent this problem. The mesh appears to converge at the refinement level of the medium coarse mesh. The effect of impact velocities on fracture is studied on unjlexed and flexed foot models. At lower velocities, fracture is observed in the form of a single continuous crack, and a pronounced branched type of network is observed at higher velocities. Finally, variation in fracture networks due to variability in strength of the bone is studied. For lower values of failure strain, significantly larger and branched networks of fracture are observed.

Commentary by Dr. Valentin Fuster
2015;():V003T03A059. doi:10.1115/IMECE2015-52059.

Occupant injury potential to oblique loading at aircraft crash severities is unknown. The objective of the present study was to derive preliminary injury criteria for the Federal Aviation Administration (FAA) Hybrid III anthropomorphic test device (ATD) under oblique loading conditions. Twelve sled tests were conducted at four pulse severities and three configurations. An acceleration pulse representative of the one specified in Title 14 Code of Federal Regulations Part 25.562, emergency landing dynamic condition for horizontal impact was used as an input. Pulses were scaled in magnitude at 50, 61, 75 and 100% of the peak acceleration 13.7, 10.2, 8.6 and 6.8 m/s, respectively. The three conditions were: 45-degrees, no arm rest, pelvis restrained with two belts, legs restrained; 45-degrees, with arm rest, single lap belt, legs restrained; 30-degrees, no arm rest, two lap belts, legs unrestrained. The ATD was placed on a generic seat representative of aircraft seat geometry and the seat was oriented obliquely. ATD accelerations, thoracic and lumbar spine forces, and restraint forces were recorded. Peak tension forces in the thoracic and lumbar spine ranged from 10–12.7 kN at the highest pulse to 3.6–4.2 kN at the lowest pulse. Previously reported in-house post mortem human surrogate (PMHS) tests provided a matched-paired dataset for combining injuries with ATD metrics. From this limited sample set, 5.2 kN tension force in the spine is suggested for the FAA-Hybrid III ATD as a preliminary injury criteria in oblique loading in the aviation environment.

Topics: Aircraft , Wounds
Commentary by Dr. Valentin Fuster
2015;():V003T03A060. doi:10.1115/IMECE2015-52108.

Lower neck injuries inferior to C4 level, such as fractures and dislocations, occur in motor vehicle crashes, sports, and military events. The recently developed interaction criterion, termed Nij, has been used in automotive safety standards and is applicable to the upper neck. Such criterion does not exist for the lower neck. This study was designed to conduct an analysis of data of lower neck injury metrics toward the development of a mechanistically appropriate injury criterion. Axial loads were applied to the crown of the head of post mortem human subject (PMHS) head-neck complexes at different loading rates. The generalized force histories at the inferior end of the head-neck complex were recorded using a load cell and were transformed to the cervical-thoracic joint. Peak force and peak moment (flexion or extension) were quantified for each test from corresponding time histories. Initially, a survival analysis approach was used to derive injury probability curves based on peak force and peak moment alone. Both force and moment were considered as primary variables and age a covariate in the survival analysis. Age was found to be a significant (p<0.05) covariate for the compressive force and flexion moment but insignificant for extension moment (p>0.05). A lower neck Nij formulation was done to derive a combined interactive metric. To derive cadaver-based metrics, critical intercepts were obtained from the 90% injury probability point on peak force and peak moment curves. The PMHS-based critical intercepts derived from this study for compressive force, flexion, and extension moment were 4471 N, 218 Nm, and 120 Nm respectively. The lower cervical spine injury criterion, Lower Nij (LNij), was evaluated in two different formulations: peak LNij and mechanistic peak LNij. Peak LNij was obtained from the LNij time history regardless of when it occurred. Mechanistic peak LNij was obtained from the LNij time history only during the time when the resulting injury mechanism occurred. Injury mechanism categorization included compression-flexion, compression-extension, and those best represented by a more pure compression-related classification. Mechanistic peak LNij was identified based on the peak timing of the injury mechanism. Peak LNij and mechanistic peak LNij were found to be significant (p<0.05) predictors of injury with age as a covariate. The 50% injury probability was 1.38 and 1.13 for peak LNij and mechanistic peak LNij, respectively. These results provide preliminary data based on PMHS tests for establishing lower neck injury criteria that may be used in automotive applications, sports and military research to advance safety systems.

Topics: Biomechanics , Wounds
Commentary by Dr. Valentin Fuster
2015;():V003T03A061. doi:10.1115/IMECE2015-52631.

Light body armor development for the warfighter is based on trial-and-error testing of prototype designs against ballistic projectiles. Torso armor testing against blast is virtually nonexistent but necessary to ensure adequate mitigation against injury to the heart and lungs. In this paper, we discuss the development of a high-fidelity human torso model and the associated modeling & simulation (M&S) capabilities. Using this torso model, we demonstrate the advantage of virtual simulation in the investigation of wound injury as it relates to the warfighter experience. Here, we present the results of virtual simulations of blast loading and ballistic projectile impact to the torso with and without notional protective armor. Our intent here is to demonstrate the advantages of applying a modeling and simulation approach to the investigation of wound injury and relative merit assessments of protective body armor.

Commentary by Dr. Valentin Fuster
2015;():V003T03A062. doi:10.1115/IMECE2015-52696.

A microscale model of the brain was developed in order to understand the details of intracranial fluid cavitation and the damage mechanisms associated with cavitation bubble collapse due to blast-induced traumatic brain injury (TBI). Our macroscale model predicted cavitation in regions of high concentration of cerebrospinal fluid (CSF) and blood. The results from this macroscale simulation directed the development of the microscale model of the superior sagittal sinus (SSS) region. The microscale model includes layers of scalp, skull, dura, superior sagittal sinus, falx, arachnoid, subarachnoid spacing, pia, and gray matter. We conducted numerical simulations to understand the effects of a blast load applied to the scalp with the pressure wave propagating through the layers and eventually causing the cavitation bubbles to collapse. Collapse of these bubbles creates spikes in pressure and von Mises stress downstream from the bubble locations. We investigate the influence of cavitation bubble size, compressive wave amplitude, and internal bubble pressure. The results indicate that these factors may contribute to a greater downstream pressure and von Mises stress which could lead to significant tissue damage.

Commentary by Dr. Valentin Fuster
2015;():V003T03A063. doi:10.1115/IMECE2015-53033.

This paper presents a study to provide guidance on the use of body-worn blast overpressure sensors to predict the risk of blast induced closed head trauma and lung injury. Data collected from blast sensor systems, when used in combination with modeling and simulation, can recreate the full loading on the warfighter [1]. Using field blast data from a 4 sensor time-synched blast system, the incident blast wave and direction was reconstructed and used as input to computational fluid dynamic (CFD) simulations of blast impacting an outfitted warfighter. Pressures around the head and underneath the helmet were found to be in agreement with experimental data. The peak resultant head velocity, which is shown to be a correlate of concussion, was also found to correlate with incident impulse over a wide range of blast conditions. Lung injury was assessed for every blast condition, revealing that some blast directions and intensities more readily engage multiple modes of injury. With the accurate reconstruction of the true blast loading to a warfighter, damage correlates obtained from biomechanical modeling analysis can be calculated for correlation with medical outcomes.

Topics: Lung , Wounds
Commentary by Dr. Valentin Fuster
2015;():V003T03A064. doi:10.1115/IMECE2015-53542.

Recent studies on military breachers in training environments suggest that there are neurocognitive risks from exposure to repeated low-level blasts. However, the dose accumulation effects from multiple low-level blast exposures and their relation to mild traumatic brain injury (mTBI) are not well understood. This paper presents a controlled neurobehavioral study of behavioral effects from repeated low-level blasts delivered at ten second intervals using a rat model.

A custom designed shock tube was developed to deliver repeated low-level blasts to rats at short intervals on the order of seconds. A total of 192 rats were divided into three cohorts of 64 for testing. Each cohort was exposed to a different blast intensity (7.5, 15, or 25 psi reflective pressure with durations <0.25 ms), and each cohort was further divided into four levels of blast repetition (0, 5, 10, or 15 repeats). Shock tube blasts were directed at the rat’s head, and startle with prepulse inhibition (PPI) and fear learning and extinction behavioral tests were performed to evaluate the blast effects.

Behavioral testing results showed that repeated low-level blasts can affect PPI and contextual fear recall. PPI was not affected by repeated exposures to 7.5 psi blasts, but repeated 15 and 25 psi blasts disrupted PPI. All cohorts showed significant fear learning, but the highest blast group (25 psi, 15 repeats) had disruptions in spatial memory recall. None of the cohorts showed effects on cued fear recall or fear extinction and retention. The data collected are being used in continuous research to understand how the behavioral changes relate to mTBI, and how these animal tests can be scaled and modeled to interpret possible outcomes for humans.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Dynamics and Control of Biomechanical Systems

2015;():V003T03A065. doi:10.1115/IMECE2015-50533.

The human upper airway (UA) dynamic characteristics differ from healthy subjects to obstructive sleep apnea (OSA) patients. Having a common term of reference for comparison is very difficult as many anatomical parameters are involved; namely: volume of airway, uvula, tongue, and air gaps at the rear of the mouth. This study investigates these characteristics for healthy and OSA subjects and proposes new common ground parameters for comparison. The objective of this study is to identify the causes of collapse by comparing these characteristics between those subjects. Magnetic resonance imaging (MRI) data of the UA expanding from nasopharynx to the hypopharynx were conducted on 8 healthy subjects and 10 OSA patients. 3D models were constructed and simulated. Measurements of the UA were evaluated and compared in both groups. The outcomes support the fact that the air volume is not the main contributor for the UA collapse and show that the apneic events are caused by the large size of the tongue and uvula. Finally, the natural frequencies for the uvula and tongue were very close in both participating groups.

Commentary by Dr. Valentin Fuster
2015;():V003T03A066. doi:10.1115/IMECE2015-50564.

This paper presents the analysis of a third-order linear differential equation representing the control of a muscle-tendon system, during quiet standing. The conditions of absolute stability and critical damping are analyzed. This study demonstrates that, for small oscillations, when the gravitational effect is modeled as a destabilizing negative stiffness and muscle-tendon stiffness is positive, the energy required to reach a critically damped state is very high. The high energy consumption is a consequence of a specific high threshold of muscle-tendon stiffness needed to achieve critical damping.

An approximated graphical method confirms that during a hold and release paradigm intended to perturb quiet standing, the ankle response to fall recovery is proper of a third-order system. Furthermore, a direct estimation of the muscle and tendon parameters was obtained.

Commentary by Dr. Valentin Fuster
2015;():V003T03A067. doi:10.1115/IMECE2015-50567.

This paper presents the simulation and fabrication of a bipedal humanoid system actuated with linear springs to produce a standing equilibrium position.

The humanoid system is comprised of two leg assemblies connected by a hip bracket. Eleven pairs of springs were attached to the system in locations designed to simulate the muscles and tendons in a human body. The assembly was modeled in the multi-body dynamics simulation software SimWise 4D. Simulations were performed to determine the springs’ stiffness and natural lengths using a top-down heuristic approach. After a set of springs were found to produce a good simulated stable position, they were cross referenced to standard commercially-available parts. A final simulation was then performed to verify that the real-world spring values produced a stable system.

Working in tandem with SimWise 4D, the humanoid assembly was fabricated using PLA plastic via an extrusion-type rapid prototyping machine. From the results of the simulation, the set of working springs were implemented onto the plastic model. After final modifications, the assembly then produced a standing equilibrium position. Finally, the assembly was perturbed in several directions to ensure that after the system experienced a displacement it would then return to its original position.

Commentary by Dr. Valentin Fuster
2015;():V003T03A068. doi:10.1115/IMECE2015-51017.

Mechanical stimuli are crucial for the growth, development, and maintenance of articular cartilage and bone. This paper investigates a novel mechanical loading device with position specific loading capability for stimulating articular cartilage and bone. It proposes a design of an under-actuated multi-fingered robotic hand for achieving such a joint loading. The robotic hand has 8-degrees of freedom and is operated by a single motor. Four fingers, each having two phalanges were designed. The fingers are connected through shafts and are operated using a slider crank mechanism. The CAD model was constructed in Creo and then exported to Simmechanics, a toolbox in MATLAB / SIMULINK module where dynamic force analysis was performed. The simulation results validate that the device can produce the necessary magnitude of forces at required frequencies to promote the stimulation of articular cartilage and bone growth.

Commentary by Dr. Valentin Fuster
2015;():V003T03A069. doi:10.1115/IMECE2015-51331.

This paper deals with human knee and hip joints’ forces in moderate squatting motion. The model developed for squatting is validated through simulations for walking (the stance phase of gait cycle) which are compared with data available in the literature. The knee model is two dimensional and includes tibia, femur, ligamentous knee structures, and muscles. The model is used to investigate the ligament, contact and muscle forces during both moderate squatting and walking.

Commentary by Dr. Valentin Fuster
2015;():V003T03A070. doi:10.1115/IMECE2015-52290.

Inertial and magnetic sensors are commonly used to determine orientation as they do not rely on a line of sight [1, 2]. There are many different techniques to fuse inertial measurement unit (IMU) data and obtain useful rotational data [1–3]. This study uses two separate data fusion techniques; a direction cosine matrix-based (DCM) technique and a quaternion-based Extended Kalman Filter (EKF) technique [1–3]. These techniques were altered based on performance metrics to weight sensor data when certain sensors proved not as reliable as others [2]. IMU sensors were tested on a hand mannequin and filters were developed using MATLAB software. Simulation results displayed a root-mean-squared error of less than .06° for each rotation angle. Experimental results maintained errors of less than 8° in each rotation angle.

Commentary by Dr. Valentin Fuster
2015;():V003T03A071. doi:10.1115/IMECE2015-52450.

Shaken Baby Syndrome is a collection of injuries that have been associated with the violent shaking of an infant or small child. These injuries can then lead to serious brain damage or even death. It is therefore important to identify the exact mechanism that leads from the shaking to the observed injuries, but little experimental work has been done in this area.

The first part of this study was designed to identify if a correlation exists between the physical characteristics of a person shaking a crash test dummy (CRABI) and the resulting accelerations and jerks associated with the motion of the dummy’s head. This was done by placing a three axis accelerometer in the head and two in the body (one in the chest and one in the groin) of a median twelve month old male dummy to determine the acceleration of the head and body. In particular, the relative angular acceleration and jerk of the head relative to the body was determined, since it was felt to be a better predictor of brain damage than would be the absolute linear acceleration of the head.

Similar work has been done in the past; however that study only considered the absolute acceleration of the head, and in only one direction. Since the present study allows the attitude of the head to be determined, a true relative angular acceleration of the head relative to the body was found. Consequently, it was found that no strong correlation existed between the absolute linear acceleration and any body characteristic, however a correlation (R2) of 0.6 was found to exist between the body weight of the shaker and the maximum angular jerk of the dummy’s head relative to its body, as compared to only a correlation of 0.5 when the shaker’s body weight was compared to the absolute linear acceleration of the head.

A two dimensional dynamic simulation was also developed that modelled the behavior of a child crash test dummy. The model included the legs, torso, and head of the dummy, and the elastic behavior of the neck. The model was created to allow the associated accelerations and jerks to be determined for inputs of various magnitude and temporal profiles. The model was then validated by comparing the simulation results to the test results obtained from the experimental study described above.

Commentary by Dr. Valentin Fuster
2015;():V003T03A072. doi:10.1115/IMECE2015-53191.

Mechanical loading of the knee is an innovative modality developed for rehabilitation of the knee joint as well as the femur and tibia that are subjected to bone fractures, osteoarthritis and osteoporosis. Loading essentially applies a lateral and periodic force to the knee joint [1]. In this paper, we propose the design of an electro-mechanical device that is capable of applying such dynamic loads. The key variable attributes of this device are the magnitude of the loading force, together with displacement and frequency. A DC motor with a controller actuates the device to produce the necessary force. The loading force is applied to the knee by a set of pads in a restricted linear motion. The operation of the device is approximated using the software package, SimMechanics of MATLAB. The simulations show that the device is capable of producing a suitable loading force with desired frequency. This simulation helps in constructing the device and performing experiments with appropriate frequencies. The device is expected to stimulate the fluids in porous skeletal matrix, resulting in strengthening the knee and bones. It can be employed for clinical trials for necessary evaluations and improvements.

Commentary by Dr. Valentin Fuster
2015;():V003T03A073. doi:10.1115/IMECE2015-53229.

The human knee is a complex and robust system. It is the most important joint for human gait because of its immense load bearing ability. The loss of such an important joint often makes it difficult for a person to ambulate. Because of this and the resulting unnatural application of forces, many trans-femoral amputees develop an asymmetric gait that leads to future complications. Prosthetic knees are required to be well-designed to cope with all variabilities. There have been many prosthetic knee designs, some more complex than others. This paper describes the design and preliminary testing of a novel passive position and weight activated knee locking mechanism for use in lower limb prosthetics. This knee mechanism is designed to be a simple and economical alternative to existing knee mechanisms. The mechanism utilizes the dynamics of the user to lock the knee during stance and unlock during the swing phase. The presence of one moving component and a simple assembly makes this design a good base for customization. Results from testing the knee mechanism shows trends that are different from a normal human knee, which is to be expected. The prosthetic knee is designed to have low friction during swing of the shank and, hence, the flexion and extension angles and angular velocities are larger compared to a normal knee. The kinematics show a cyclic trend that is highly repeatable. Further refinement and testing can make this mechanism more efficient in mimicking a normal knee.

Topics: Weight (Mass) , Knee
Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: General Biomedical and Biotechnology Applications

2015;():V003T03A074. doi:10.1115/IMECE2015-50984.

Hydrogen sulfide (H2S) detection is an important capability for applications that range from environmental to biomedical use. In medical application, hydrogen sulfide may be an effective marker for various cardiovascular diseases. This work reports progress on H2S detection using a unique lab-on-a-chip device designed specifically for both environmental and biomedical applications. The chip consisted of three distinct layers of PEO/PDMS structures which have been bonded using various techniques including Reactive Ion Etching (RIE). First layer consisted of capillary channels to organize the flow of the sample. Also, liberation of the sulfide took place at this layer. The second layer was a H2S selective membrane. The third layer consisted of trapping chamber where trapped H2S samples were withdrawn for the quantification of H2S concentration. Fabrication of the first layer was accomplished using photolithography technique. Specifically, the chip incorporated unique design features and operation with advanced liberating chemistry that effectively released H2S from aqueous solutions introduced to the device. Mixture of poly-dimethylsiloxane-ethylene oxide polymeric (PDMS-b-PEO) and polydimethylsiloxane (PDMS) was cast on Su8 mold which produced super hydrophilic channels that allowed liquid flow via capillary action. The chip has been both fabricated and characterized as reported in this work. For each sample, 150 μL of the reaction volume was loaded in an HPLC vial and analyzed by a Shimadzu Prominence HPLC equipped with fluorescence detection and an eclipse XDB-C18 column. Sulfide transfer increased steadily at a rate of approximately 2% per minute until peaking at approximately 60% at 30 minutes. Percent transfer data show that sulfide diffused into the trapping chamber in a reproducible manner and that it was stable once it reached its peak at 30 minutes. Characterization and testing of the fully assembled device indicates significant promise and utility. Additional improvements may be made by optimizing parameters such as the decreasing ratio of the chamber volumes to the membrane area and the membrane thickness. The performance of this microfludic device was attributed to hydrophilic surface of PEO/PDMS, strong bonding of the chip using 3M transfer tape and well suited PDMS membrane that allow selective diffusion of hydrogen sulfide.

Topics: Hydrogen , Biomedicine
Commentary by Dr. Valentin Fuster
2015;():V003T03A075. doi:10.1115/IMECE2015-51117.

In this study, we would like to develop a portable round argon atmospheric-pressure plasma jet (APPJ) which can be applied for general use of bacteria inactivation. The APPJ was characterized electrically and optically, which include measurements of absorption power, gas temperature and optical properties of plasma generated species. Measured OH* number density at 5 mm downstream was estimated to be 5.8 × 1015 cm−3 and the electron density and electron temperature were estimated to be 2.4 × 1015 cm−3 and 0.34 eV, respectively, in the discharge region. This APPJ was demonstrated to effectively inactivate E. coli within seconds of treatment, which shows its great potential in the future use of general bacteria inactivation and sterilization.

Commentary by Dr. Valentin Fuster
2015;():V003T03A076. doi:10.1115/IMECE2015-51595.

Neural tissue engineering has emerged as a promising alternative to address various nerve injuries. Particularly, advancement in both 3D biomimetic scaffold fabrication strategies and nanotechnology has inspired this field into a new era. In this study, we fabricated a novel 3D biomimetic scaffold, which has tunable porous structure and embedded core-shell nanoparticles with neurogenic factor delivery system, using stereolithography (SL) based 3D printing and core-shell electrospraying techniques. Our results indicated that scaffolds with higher porosity significantly improve PC-12 neural cell adhesion compared to ones with smaller porosity. Furthermore, scaffolds embedded bovine serum albumin (BSA) containing nanoparticles showed an enhancement in cell proliferation relative to bared control scaffolds. In addition, confocal microscopy images illustrated that the scaffold with nerve growth factor (NGF) nanoparticles increased the length of neuritis and directed neurite extension of PC-12 cells along the fiber. The results in this study demonstrate the potential of this 3D scaffold in improving neural cell function and nerve growth.

Topics: Nanoparticles , Shells
Commentary by Dr. Valentin Fuster
2015;():V003T03A077. doi:10.1115/IMECE2015-52769.

Here we present initial experiments towards an integrated platform for single cell selection, manipulation and lysis. The premise is that an array of polarized conical carbon electrodes can be dipped in a cell culture, trap cells of interest using dielectrophoresis and transport them to specific locations where they can be lyzed electrically. We aim at developing an automated tool to extract intracellular components from targeted particles over specific locations, i.e., a DNA microarray or other functionalized spots. What we contribute in this work is modeling of the electric field and its gradient around carbon cones, as well as initial cone fabrication results. To the best of our knowledge, both the fabrication of conical glassy carbon electrodes and the general concept of the proposed platform are novel. Ongoing work is on demonstrating cell trapping and lysis using these conical electrodes by only varying the magnitude and frequency of their polarizing AC signal.

Topics: Carbon , Electrodes
Commentary by Dr. Valentin Fuster
2015;():V003T03A078. doi:10.1115/IMECE2015-52816.

Cryotherapy, also called cryosurgery, cryoablation or targeted cryoablation therapy, is a minimum invasive treatment that uses extreme cold temperatures to freeze and destroy damage tissue, like tumors or cancer cells. During cryotherapy, a refrigerant as liquid nitrogen or argon gas is forced to flow inside a probe. This probe is similar to a needle and it is called cryoprobe. Once the refrigerant is inside this cryoprobe the temperature decreases below zero Celsius in a given time, creating an intense cold that contacts the diseased tissue. Physicians use image guidance techniques to monitor the cryoprobe, such as ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI). To destroy diseased tissue located outside the body, liquid nitrogen is applied directly to the infected zone with a cotton swab or spray. For tumors located below the skin surface and depth in the body, the medical image guidance to insert one or more cryoprobes is used. Living tissue, whether healthy or sick, cannot tolerate extremely low temperatures. For this reason cryotherapy involves a series of steps leading to cell death. Tumors are repeatedly frozen and thaw, typically two freeze – thaw cycles are used. Once the cells have been destroyed, white blood cells of the immune system remove dead tissue.

The present work is a 3D simulation. The skin is modeled with a regular geometry, divided into three layers: epidermis, thinner and superficial part of the skin; dermis, 40 times thicker than the epidermis (also this layer has a thermoregulatory function because of the blood flow, which also contributes to vasoconstriction and vasodilatation of the skin), and finally the last layer is the hypodermis or subcutaneous fat layer (which mainly stores fat). For a transient analysis of this three layers of the skin, the bio-heat transfer equation of Pennes is used, since it contains terms that involve energy released during metabolism, blood perfusion, body core temperature and certain physical properties such as density, specific heat, thermal conductivity, latent heat of phase change and heat capacity ratio. The malignant tumor, melanoma, is modeled as an irregular symmetric geometry. Three different melanoma Clark levels are analyzed, Clark II, III and IV. Each level is analyzed with three size variations. These levels are chosen because most people who are diagnosed with melanoma have Clark II level. Clark V level was not considered because when melanoma reaches subcutaneous cellular tissue the metastasis process begins. In this work a thermal recovery analysis of the skin during certain periods of time in the freezing-thaw cycles is carried out. Each of this time periods vary according to the type of refrigerant, liquid nitrogen or argon gas. The analysis contemplates the phase change suffered by the skin.

Topics: Tumors
Commentary by Dr. Valentin Fuster
2015;():V003T03A079. doi:10.1115/IMECE2015-53241.

Analysis of isolated cancer cells in circulation is proven to help determine the success of the cancer treatment and understand the genetic signature of cancer disease. Scarcity of these cells in blood circulation (1–10 CTC in 1ml blood) however, makes the isolation process extremely challenging. Ever improving CTC isolation methods fall into two main categories: 1.Immunomagnetic separation based on antibody binding to tumor specific biomarkers expressed on the cell 2. Physical separation based on the size of the CTCs. Efficiency in cell isolation is still low in these techniques due to the variation in expression level of tumor specific antigens and tumor cell size. Therefore, tumor cell isolation strategies using new CTC biomarkers must be explored.

In this study, we investigated the feasibility of using mechanical stiffness difference in order to detect and isolate the circulating tumor cells from the blood cells. AFM nanindentation experiments revealed that cancer cells are significantly softer than the surrounding white blood cells and therefore, stiffness can be used as a biomarker for CTC isolation. In addition, finite element analysis simulations have shown that CTC isolation can be performed at high efficiency using stiffness-based isolation. Therefore, stiffness based isolation has a potential to achieve fast, label-free isolation of CTCs at high efficiency for clinical applications.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Posters

2015;():V003T03A080. doi:10.1115/IMECE2015-51006.

The aim of this paper is to design and develop a low-cost prosthetic arm based on surface electromyography (sEMG) signal activities of the biceps muscle during upper-limb movement. Different methods are described in the literature, but many problems are encountered in dealing with the online processing of raw EMG (rEMG) signals, such as signal sampling and memory requirements. In this paper, the enveloped EMG (eEMG) signal is used as a control signal that reduces signal sampling rate and memory requirements. The relationship between elbow motion and the activity level of the biceps muscle is characterized using relevant extracted features (root mean square (RMS)). Validation of the proposed low-cost system is conducted using comparison with a professional biomedical system (Bioback MP150). In addition, the estimated equation of movements of each subject is estimated based on the recorded data. From this equation, the angle of motion is calculated as the control of the movement of the robotic arm. Finally, the system proposed in this paper considers the eEMG signal rather than the rEMG signal and deals with the signal based on a sample of 1 KHz rather than 10 KHz. This system reduces our target cost (reduction in hardware requirements and processing time) with acceptable accuracy. The experimental results illustrate that the eEMG signal has the same features-print as that of the rEMG signal, and the eEMG signal can generate the control signal required to move the prosthetic arm.

Commentary by Dr. Valentin Fuster
2015;():V003T03A081. doi:10.1115/IMECE2015-51911.

Introduction and Objectives: The dental prostheses are typical biomechanical structures because they have the objective to restore the mastication functions and are responsible for replacing the original tooth that was damaged. In the last few years, many studies have been done and big achievements have been noticed in this area. However, clinical studies and experimental procedures for these conditions are sometimes impractical, due to the biological nature of these components and the difficult to reproduce and to analyze such conditions. Moreover, it involves complex geometries, loads and mechanical behaviors, which analytical solution is very difficult to achieve. For these reasons, many researchers have applied the Finite Element Method (FEM). This method allows the evaluation of non-linear situations (e.g. biomechanical interactions) with complex geometries where experimental tests are usually difficult to be conducted. Furthermore, the uses of this method allow failure evaluation and it forecast occurrence. Like any mechanical structure, prostheses are sensible to failures. The cyclic nature of the loading that components are exposed means that fatigue failures are the type of failure which needs more attention in these kinds of structures. Therefore, this project aims to develop a tridimensional finite element model of dental prosthesis in order to evaluate the fatigue problem. Methods: A geometric model from a single dental prosthesis compounded by an implant, an abutment screw, an abutment, a fixation’s screw and a crown will be generated from Micro CT and scanning data. Then, the geometry will be exported to finite element software where a finite element model will be created. After these steps, boundaries conditions will be applied and simulations will be done. Finally, the simulation results will be analyzed. Results: The results from fatigue simulations and analysis demonstrated that abutment screw will have a finite life in most of the analyzed cases, and the fixation screw will be an infinite life. Conclusion: The results obtained illustrate the efficiency of Finite Element Method on simulating the biomechanical conditions, mainly in dental prostheses. In this study, the fatigue conditions were explored and analyzed. Finally, the knowledge about this problem could be improved.

Commentary by Dr. Valentin Fuster
2015;():V003T03A082. doi:10.1115/IMECE2015-52476.

In the 1960’s, Brånemark and colleagues developed a dental implant system using a direct attachment to bone structure without generating soft tissue. This phenomenon called osseointegration involves biomechanical behavior of materials. In several studies it has been verified that the surface treatment on titanium implant has been the main factor for the osteogenesis process and, consequently, osseointegration [1, 2, 3]. Treated titanium surfaces have better conditions for cell adhesion that can lead to load application in the shortest time.

The aim of this study was to evaluate the surface energy and the cell osteogenesis on titanium discs under different conditions of blasting and acid attack. Osteoblastic cells Hfob 1.19 were used to measure cell culture parameters like cell viability and cell proliferation, alkaline phosphatase activity and mineralized nodule formation. Osteogenesis cell was defined through a mathematical model proposed by a similitude in engineering with osteogenic parameters analyzed in culture cells.

Fowkes Theory was used to calculate the surface energy by measuring contact angles between liquid sensors (Deionized Water, Chloroform) on different titanium surfaces.

Significant difference (P < 0,01) was observed for surface energies ranging between 26,76 a 33,81 mJ/m^2 using ANOVA and Bonferroni test. It was noted that the highest surface energies are related with osteogenesis levels.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Quantitative Biomedical Image Analysis

2015;():V003T03A083. doi:10.1115/IMECE2015-50055.

Melanoma is one of the most deadly skin cancers and amounts for ∼79% of skin cancer deaths. Early detection and timely therapeutic action can reduce mortality owing to melanoma. In this study, we demonstrate the feasibility of our in-house skin image classification framework, trained based on a library of normal as well as pathological skin images, for automatic feature extraction and detection of melanoma. The described framework begins with active contour segmentation the skin images followed by extraction of both color and texture features from the segmented image and employs a neural network classifier to for trained identification of melanoma cases. Training and testing was conducted using a 10-fold cross validation strategy and led to 88.06% ± 1.65% accuracy in classification of melanoma images.

Topics: Skin
Commentary by Dr. Valentin Fuster
2015;():V003T03A084. doi:10.1115/IMECE2015-50206.

Genu valgum is a cause of knee pain and early arthritis which requires therapeutic action with external braces or surgery at a young age. This paper describes an image processing workflow and validation study for automatic characterization of the valgus deformity (i.e. genu valgum) from tibio-femoral x-ray radiographs. We implement an image processing pipeline starting with basic filtering and bone segmentation, followed by application of a Hough transform to determine the centerline of the diaphyses of the femur and tibia based on which a TF subtended angle is measured for each leg. Feasibility of this workflow is demonstrated on 21 short TF radiographs. The automatically computed angles were highly correlated (r2 = 0.85 and p≪0.001) to the ground truth with a mean absolute error as low as 1.97°.

Commentary by Dr. Valentin Fuster
2015;():V003T03A085. doi:10.1115/IMECE2015-51703.

Pores (namely lacunae, clusters of canaliculi, Haversian canals, and resorption cavities) are present throughout cortical bone. This paper characterizes the area fraction (AF, %)) of each type of these pores as function of distance from the bone’s geometric center while noting the region in which such pores are located: midcortical or periosteal.

Optical slides (at 20X) are taken from 2 cortical bone biopsies named bone 1 and bone 2 and cut at mid-diaphysis femur from 2 different (about 2 year-old) bovine cows. The slides are collected from posterior (pericortical) and anterior (intracortical) locations. The area of each of these biopsies is about 2.5mm × 3mm located near the outer cortex of the bone. In polar coordinates from the bone’s center, the areas cover radial distance of about 3.3 mm (of radius, R) and encompass an arc of 10°.

Automated segmentation is used to locate and identify all pores in the optical slides the shapes of which are best fitted into ellipses. Values of area fraction, AF (%) of said fitted ellipses are then automatically calculated in secondary osteons for both regions. Variations in values of area fraction AF (%) are related to actual areas of pores (based on their defining equations).

Observations suggest that area fractions (%) of all pores (but to lesser degree for Haversian canals), to significantly decrease linearly and in a steep fashion with R (statistically significant, p < 0.01) in the anterior region where osteonal growth is expected to have continued to develop. However, in the posterior region where osteonal growth appears to have matured, area fraction (%) values seem to have reached a steady state resulting in fairly flat behavior versus R. All observations are equally applicable for biopsies collected from bone 1 and bone 2.

Topics: Bone , Porosity
Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Sport Biomechanics

2015;():V003T03A086. doi:10.1115/IMECE2015-50550.

Exercise-induced bronchoconstriction (EIB) and Exercise-induced asthma (EIA) are used synonymously to describe acute lung airway narrowing occurring during and/or after exercise. Tools usually used by health practitioners to assess the severity of EIB or EIA symptoms include bronchodilator tests and various bronchial provocation procedures including spirometer and eucapnic voluntary hyperpnoea (EVH) challenge system, there is no tool that is able to monitor the severity of acute lung airway narrowing. This study aims to design a graphical user interface (GUI) to monitor the severity of acute lung airway narrowing using MATLAB software. The GUI will present the measurement data into a simple and user-friendly program consisting of patient information, EVH test analysis and detection of EIA and EIB. Success of this project widens the usage of EVH challenge in medical areas and the GUI may serve as a new clinical computer-aided diagnostic tool to help healthcare professionals non-invasively monitor the severity of asthma, EIA and EIB.

Commentary by Dr. Valentin Fuster
2015;():V003T03A087. doi:10.1115/IMECE2015-50881.

The objective of this study is to conduct biomechanical simulation for a musculoskeletal of archery performance. The simulation aims to find the movement patterns in working postures, the muscle activity and joint reaction forces. The results obtained are discussed and the work presented can help analyze the utilization of various muscles during the performance of the repetitive motion of archery.

Commentary by Dr. Valentin Fuster
2015;():V003T03A088. doi:10.1115/IMECE2015-52041.

The objectives of this study is to investigate the transduction of blast wave through the SAS region and the influence of SAS including different types of trabeculae in reducing the strain in the brain, when the head is subjected to a blast wave, and finally, comparing that to a none blast load such as blunt impacts or angular accelerations of the head during contact sports or accidents. This is accomplished through a series of Global/Local models of the head, neck and the brain. Specifically, a validated FE 3D model of the head and neck is subjected to a blast wave and the time dependent local compressive pressure gradient on the dura matter is calculated. Then through several detailed local FE models of the head, consisting Dura mater, Gray matter, Subarachnoid space having trabeculae and the CSF, the strains in the brain are calculated. In the local models different architecture and morphology of the trabeculae (rod shaped and the tree-shaped) are considered. The Global/Local models were analyzed using ABAQUS 6.12. In addition, the same procedure has been carried out for a velocity impact profile corresponding to 1.1 mph. The results revealed that the shape of the trabeculae would not affect the severity of loads transferring to the brain from shock waves in blast scenarios. Moreover, the interaction between the CSF and Tree-shaped trabeculae and rods with smaller cross sections, protect the brain better in impacts.

Topics: Waves , Brain
Commentary by Dr. Valentin Fuster
2015;():V003T03A089. doi:10.1115/IMECE2015-52072.

The American kettlebell swing is a variation of the Russian kettlebell swing where the kettlebell is swept in an arc from between the legs to an overhead position with straightened arms. Previous studies involving the kettlebell swing have examined the aerobic and cardiovascular impact of the swing, the variation of mechanical impulse and power generation with kettlebell weight, and compared its efficacy to other types of exercises. However, there have been limited studies examining the dynamic biomechanical loads of the swing on the arm and shoulder. The aim of this study was to establish the mechanical demands of the American kettlebell swing exercise on the arms and shoulders to determine the regions of highest force output and the variation of the forces throughout the swing, all based on percentage of the swing completed. In order to obtain kinematic data, two female subjects with prior kettlebell exercise experience performed one set of fifteen American swings with 8kg and 12kg kettlebells. Position and orientation data was recorded during trials for the kettlebell, joints, and centers of mass of arm segments. Velocity and acceleration data was found using finite-difference approximations. An inverse dynamics method applied to (2-D) planar motion using Newton-Euler equations was used to determine the forces and moments at various joints along the entire arm including the wrist, elbow, and shoulder joints. Data was time normalized as percent of swing, where 0% and 100% indicated the beginning and end of the swing respectively, and approximately 50% denoted the transition between upswing and downswing halves. Results revealed that the arm was under tension during 0% to 35% and 67% to 100% of the swing, indicating the upper torso works to provide the normal force to support the curved motion of the kettlebell. During 36% to 66% of the swing the arm muscles worked in order to support the weight of the kettlebell over the head. While the lower extremity mechanical demands associated with kettlebell swings have been studied, the current results help clarify the upper extremity mechanical demands associated with kettlebell swing exercise. The results of this analysis will better help practitioners to understand the prerequisite upper extremity function needed to perform the full American style swing. The American kettlebell swing carries risks its Russian equivalent does not have, typically breaking form to make the shoulder extension involved with raising the kettlebell above the subjects head. These results suggest that the extra range of motion in the American kettlebell swing prompts different mechanical demands which, in turn, targets different muscle groups from the lower half of the American swing or the Russian kettlebell swing. Finally, because increasing mechanical stimuli is an important component to exercise progression, this analysis fills the void of understanding the effects of changing kettlebell loads on the upper extremity demands. Future research will consider the symmetry of the upper extremity mechanical patterns revealed by this analysis.

Topics: Biomechanics
Commentary by Dr. Valentin Fuster
2015;():V003T03A090. doi:10.1115/IMECE2015-52240.

Upper extremity plyometric exercises show potential for shoulder injury prevention and rehabilitation. Plyometric exercises are physical activities in which muscles are extended and contracted in a rapid and repetitive manner. An example of a plyometric shoulder exercise consists of repeatedly throwing and catching a medicine ball into a trampoline system as quickly as possible. However, proper characterization of the efficacy of the exercise requires knowledge of ball contact events; specifically, the ball contact and release times. The objective of this work was to design and test a low cost touch activated glove system that could be used to determine contact events during upper extremity plyometric exercises. The sensor design consists of a neoprene frame over which layers of Velostat® film and copper fabric are arranged to create a pressure sensitive on-off switch. Individual sensors were constructed for digits II through IV and two for the upper palm area. Each sensor was attached to a nylon glove and wired to a terminal block, circuit board and battery pack situated on the back of the hand. A second nylon glove was used to cover and protect the sensors. Contact versus no contact sensor resistance was experimentally determined by measuring the sensors’ resistance when pressure was applied to various regions of the sensor contact area. This was used to anticipate the analogous contact verses no contact sensor voltage. The response time of the sensors plus measurement circuit was also determined by measuring the rise and fall time of the glove system due to contact events. Activated sensors produce a high voltage (> 3.0V) in the measurement circuit and indicate contact. The touch activated glove system was successfully used in a research study to quantify the intensity of overhand plyometric throwing and in another study to determine the biomechanical variables for the single arm seated shot put upper extremity functional performance test.

Topics: Design
Commentary by Dr. Valentin Fuster
2015;():V003T03A091. doi:10.1115/IMECE2015-52319.

Conventional equipment for muscular rehabilitation and training uses passive load systems. This work seeks the creation of an alternative resistance generation device for the skeletal muscle contraction to be applied in conventional machines of muscular training and physiotherapy. The proposed device uses a group spring-follower-cam to produce the resistance and does not use cables, belts or chains. The device was designed to generate mechanical resistance through low inertia set, accessibility, modular and low-cost to be adapted on training machines. This device consists of a cam-follower pair connected to a compression spring. Its operating principle is based on the pressure angle variation between the cam-follower pair. The mathematical modeling and the numeric solution for the cam profile is presented. It was noted that prototype can be applied in high speeds unlike conventional equipment. The maximum torque curve available and the torque curve obtained in the device approached, as the movement training approached motor gesture, with maximum errors of about 10 %. The results confirm that the device is capable of generating a resistance profile that resembles the maximum available torque profile at the joint user when performing certain movement training, which can more adequately represent the motor gesture to be trained. Two case studies were conducted using the motor gesture of judo training and rower’s movement which mainly uses elbow flexion.

Commentary by Dr. Valentin Fuster
2015;():V003T03A093. doi:10.1115/IMECE2015-53018.

Running is one of the most practiced sports around the world and it dates back to Ancient Greece. Running became an Olympic sport in 1896 and today is mostly performed for fun and to stay in shape. Nowadays, athletic shoe companies make claims on the performance of the type of shoes they manufacture. Some of their claims include shoes that allow free movements, fit like a glove, and are in complete harmony with human mechanics. The preceding characteristics are those of so-called barefoot running shoes. Robillard [1] explains that minimalist running shoes could be defined as those that provide limited or no support and only minimal protection, with the heel at the same level as the forefoot. Even though running may have been investigated, however, there is not enough analyses on barefoot running shoes. The objective of this study was to investigate the load distribution on the feet of a healthy running adult wearing barefoot shoes through experimental work and finite element analysis (FEA).

The methodology used in this study included experimental as well FEA. Tests were conducted with a 175-lb adult subject wearing a pair of minimalist shoes. Experimental data were collected and used to perform Finite Element Analysis. The barefoot shoes were modeled with an equivalent thickness of 0.453 inch, and the following parameters were experimentally determined such as the Young’s modulus of 467 psi, a density of 0.0025 lb/in3, and a Poisson’s ratio of 0.08.

The simulation results yielded a maximum compressive stress of 38.71 psi in the toe region. This stress level was approximately one-half of the stresses generated in the heel region of conventional sport shoes. This study, further, revealed the reduction of stresses at the heel region with barefoot shoes resulting in lower risk of pain and injury to the foot in the absence of impact transients ordinarily experienced with conventional shoes.

Topics: Stress
Commentary by Dr. Valentin Fuster
2015;():V003T03A094. doi:10.1115/IMECE2015-53182.

Lower extremity exoskeletons augment ability of walking, sitting and standing upright with a pair of robotic legs that ambulates the user with mobility disorder. As a mobility aid, being lightweight and compact can highly increase usability by allowing users to navigate through narrow passages. This paper summarizes the design of low profile actuators designed for minimally actuated exoskeleton, a lightweight and low profile powered medical exoskeleton developed in Robotics and Human Engineering Laboratory at UC Berkeley. An analytical method for designing low profile BLDC actuation units, critical hardware design aspects, and initial performance measurements are discussed. A set of pancake DC actuation units was designed, manufactured, assembled, and integrated into a lower limb medical exoskeleton. This exoskeleton was tested by a male 28-year-old paraplegic test pilot with injury level of T12.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Transport Phenomena in Biomedical Applications

2015;():V003T03A095. doi:10.1115/IMECE2015-50439.

After being synthesized in the soma, neuropeptides are packaged in dense core vesicles (DCVs) and transported toward nerve terminals. It is known, from published experimental results, that in terminals with type Ib boutons DCVs circulate in the terminal, undergoing repeated anterograde and retrograde transport, while in type III terminals DCVs do not circulate in the terminal. Our goal here is to investigate whether the increased DCV production in the soma can lead to the appearance of DCV circulation in type III boutons. For this purpose we developed a mathematical model that simulates DCV transport in various terminals. Our model reproduces some important experimental results, such as those concerning DCV circulation in type Ib and type III terminals. We used the developed model to make testable predictions. The model predicts that an increased DCV production rate in the soma leads to increased DCV circulation in type Ib boutons and to the appearance of DCV circulation in type III boutons. The model also predicts that there are different stages in the development of DCV circulation in the terminals after they were depleted of DCVs due to neuropeptide release.

Commentary by Dr. Valentin Fuster
2015;():V003T03A096. doi:10.1115/IMECE2015-50799.

The existence of obstructions such as tracheal stenosis has major impacts on respiratory functions. Therapeutic effectiveness of inhaled medications is influenced by tracheal stenosis, and particle transport and deposition pattern are modified. The majority of studies have focused on obstructions in branches of the airways, where the flow is diverted to the other branches to meet the needed oxygen intake. In this study we have investigated the effects of trachea with and without stenosis/obstruction on particle depositions and air flow in a human respiratory system. Patient specific CFD simulations were conducted; CT-scans of a patient with tracheal stenosis were used to create 3D models of bronchial tree up to 8 generations. The section of the stenosis was manually modified to create a healthy trachea. Comparisons between CFD simulations before and after intervention demonstrate the impact of the stenosis on flow characteristics and particles distribution. The numerical investigations were performed using the implicit Unsteady Reynolds-Averaged Navier-Stokes equation (U-RANS), using the commercially available software (STAR-CCM+) from CD-Adapco, along with K-ω; shear stress transport model. Two sets of CT-images of inhalation and exhalation were used for assigning Patient-specific boundary conditions at the outlets. Lagrangian Phase model was used to simulate particle transport and depositions of 10, 5 and 2.5 micron diameter particles. Results of the particle depositions for 10 micron particles highlight the difference in depositions and ultimately inhaled medications in patients with and without tracheal stenosis. Particle deposition for normal Tidal volume increased due to stenosis from 47% to 51% for 10 Micron particles and not a significant change for the 2.5 Micron particles (from 4.5% to 4.7%).

Comparisons of pressure drop in each generation between patient with tracheal stenosis and the healthy lung showed significant increase in pressure drop after the stenosis, which were experienced in all generations downstream. Experimental validation of the CFD results were made with a model of healthy trachea up to 3rd generation, manufactured using Additive Layer Manufacturing (ALM) from CT-images and pressure results were compared with the corresponding CFD results. Good agreements were found.

Commentary by Dr. Valentin Fuster
2015;():V003T03A097. doi:10.1115/IMECE2015-51750.

Biological sprays and aerodynamically assisted bio-jets are increasingly employed in treatment of living cells and organisms for applications in regenerative medicine, tissue repair, and advanced therapeutics. The liquid used in biological applications cover a wide range of viscosities and surface tensions. Determining conditions that achieve steady and uniform drop distribution for a range of properties of the liquid jet is critical in advancing biological applications.

In this study, numerical simulations of jet breakup are carried out using a modified volume of fluid (VOF) approach to capture the interface. The interplay of viscosity and surface tension is studied by varying liquid properties. Simulations show that a high viscosity jet stretches and elongates before a liquid segment detaches. Based on the thickness of the liquid thread connecting the detaching drop to the main liquid stream, two fundamentally different modes of liquid pinch off have been predicted: thick-thin and thin-thick. In the thick-thin mode, the liquid jet has a growing drop at its edge. As this drop grows in size, the liquid stream stretches till the drop is pinched off the liquid stream. In the other mode in addition to the pinch off of drops from the jet, ligaments of liquid break off. The change in the breakup mode is primarily governed by the relative magnitude of the viscous force compared to surface tension with high viscous force leading to thin-thick liquid stretching and pinch off. Thick-thin stretching is seen to produce slow moving satellite drops that merge backwards with the oncoming drop, while thin-thick stretching is noticed to result in faster satellite drops that merge forwards. On the other hand when surface tension force dominates, non-merging satellite drops are formed that move with a speed close to the primary drops.

Commentary by Dr. Valentin Fuster
2015;():V003T03A098. doi:10.1115/IMECE2015-52283.

Asthma treatment provided by a pressurized Metered Dose Inhaler (MDI) coupled to a Valved Holding Chamber (VHC), in cases of children younger than 5 years old, is a standard well-stablished in the medical community. The lack of experimental studies for comparison of several commercial VHC alternatives is the main goal of this study. The VHC device needs to be evaluated in terms of Fine Particle Mass (FPM) emitted and Performance. Such assessment was made based on a cascade impaction methodology (i.e. Multi-Stage Liquid Impinger - MSLI) at 30 ± 5 L/min. This impactor apparatus is composed by five stage of impaction, where the spray particle size distribution is collected by ranges of aerodynamic diameter, from coarse to fine particles. This evaluation was executed for 8 VHC devices: Aerochamber Plus®, A2A Spacer®, Compact Space Chamber Plus®, Space Chamber Plus®, Nebuchamber®, Vortex®, OptiChamber Diamond® and Volumatic®. The Ventolin® (salbutamol sulphate 100 μg/dose) was the chosen MDI device, due to its widely prescription and acceptance. Drug mass per stage was quantified by UV-Vis Spectrometry, through washing solutions of NaOH 0.01M.

Results show clear distinction between the use of MDI alone or coupled with any VHC. Its Emitted Dose (ED) is higher when coupled to a VHC, although the FPM emitted is not different. In other hand the use of VHC provides a reduction from 82.7% to 95.3% of the Throat deposition in comparison to MDI alone.

Results point the Aerochamber, Volumatic and Nebuchamber as the highest FPM emitters (27.5 ± 2.4 μg, 27.3 ± 2.7 μg, 26.5 ± 1.8 μg) and with high performance indexes (5.3 ± 0.1, 6.6 ± 1.3, 5.0 ± 0.4).

A complete device characteristics analysis is provided, showing that Throat deposition is highly related to the valve design. The Leaflet design (≈5.0 μg) has lower throat deposition than Duck type (≈9.5 μg).

A Handling and Attractiveness index is calculated and plotted against the Performance index divided by the device cost. This analysis shows that Volumatic is the best investment (1.73 ± 0.34 £−1) for home / hospital use (2.0 g−1·m−3), while the Aerochamber shows the best portability (53.2 g−1·m−3) and a reasonable investment (1.10 ± 0.02 £−1).

Commentary by Dr. Valentin Fuster
2015;():V003T03A099. doi:10.1115/IMECE2015-52606.

The effects of inhalation transience on particle transport through the lungs were examined using numerical simulation. Physiologically appropriate, regional ventilation was induced through a computed tomography (CT) based human airway geometry for steady and transient inhalation using lobar-specific boundary conditions. Transient inhalation and the analogous steady cases were simulated for two breathing rates. Particle transport was modeled for a range of particle sizes and Stokes numbers. The deposition fractions of particles were analyzed and comparisons were made between the results for steady and transient inhalation. Deposition fractions for particles released during transient inhalation were substantially less than those released during steady inhalation for all but the largest particle sizes. Future work is suggested.

Commentary by Dr. Valentin Fuster
2015;():V003T03A100. doi:10.1115/IMECE2015-53073.

The objective of this research is to develop a computational fluid dynamics (CFD) model of a healthy human aorta from the aortic arch to the femoral arteries to allow for a better understanding of blood flow characteristics in this significant vessel. The increasing number of patients suffering from vascular diseases has accelerated the research in this field. Pulsatile blood flow through the descending aorta has numerous mechanisms that influence the flow characteristics, including non-Newtonian fluid effects, transient effects of the cardiac cycle, and geometries within the aortic vessel, among others. Although CFD has been used to predict flow effects of rather complicated systems, the use of CFD in vascular flow is still largely not understood. This paper compares non-Newtonian fluid effects in the flow of a natural aorta as well as flow effects within the descending aorta, including the ostium flow diverter, which regulates blood flow from the aorta to the renal arteries and was discovered within the last five years. Utilizing Creo Parametric, a 3-dimensional representation of the aorta was created including physical portrayals of the renal, superior mesenteric, common iliac and celiac arteries. This geometry was imported, meshed, and analyzed using a commercially available CFD solver. Using fluid properties of blood previously characterized in prior research, pulsatile flow models were investigated using constant viscosity and the Carreau-Yasuda Non-Newtonian viscosity model. This research compares the Oscillating Shear Index results of the constant viscosity model versus non-Newtonian. Shear stress and velocity profiles are used to study the effects of each assumption on the flow of blood through the descending aorta. This will be done by using a scalar result of the shear stress and the calculated Oscillating Shear Index. Based on previous work, the boundary layers created at the entrance of the renal arteries should be reduced by the presence of the ostium flow diverter. The model with the ostium flow diverter is used in both simulations. Ultimately, the simulation may predict the effects of changes or interventions to the descending aorta caused by assuming constant viscosity or non-Newtonian.

Commentary by Dr. Valentin Fuster
2015;():V003T03A101. doi:10.1115/IMECE2015-53392.

Heat conduction in skin tissue is a problem of significant technological importance. A theoretical understanding of such a problem is essential as it may lead to design potential therapeutic measures for needed cancer therapy or novel medical devices for various applications including hyperthermia. To understand the physical phenomenon of energy transport in biological systems a transient model is chosen for this study. The most common transport equation to estimate temperature distribution in humans was developed by H.H. Pennes and is popularly known as the Pennes bioheat transfer equation. A generalized Pennes bioheat transfer equation accounts for the effect of various physical phenomena such as conduction, advection, volumetric heat generation, etc. are considered. In this paper, a general transient form of the Pennes bioheat transfer equation is solved analytically for a multilayer domain. The boundary value problem considers the core of the tissue is maintained at uniform temperature of 37°C, convective cooling is applied to the external surface of the skin and the sidewalls are adiabatic. The computation of transient temperature in multidimensional and multilayer bodies offers unique features. Due to the presence of blood perfusion in the tissue, the reaction term in the Pennes governing equation is modeled similar to a fin term. The eigenvalues may become imaginary, producing eigenfunctions with imaginary arguments. In addition the spacing between the eigenvalues between zero and maximum value varies for different cases; therefore the values need to be determined with precision using second order Newton’s method. A detailed derivation of the temperature solution using the technique of separation of variables is presented in this study. In addition a proof of orthogonality theorem for eigenfunctions with imaginary eigenvalues is also presented. The analytical model is used to study the thermal response of skin tissue to different parameters with the aid of some numerical examples. Results shown in this paper are expected to facilitate a better understand of bioheat transfer in layered tissue such as skin.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Vibration and Acoustics in Biomedical Applications

2015;():V003T03A102. doi:10.1115/IMECE2015-51447.

Cells respond to not only biochemical signals but also mechanical forces, which indicates that cells have some mechanosensors that convert mechanical forces into biochemical signals. According to recent reports, one of the candidates of the mechanosensors is focal adhesions that form multi-protein structures having mechanical links between intracellular cytoskeletons and extracellular matrices. Since the cellular mechanisms of sensing and responding to the mechanical stimulations at focal adhesions have not been clarified yet, we developed a micropillar substrate embedding micron-sized magnetic particles and enabling the micropillars to be cyclically deflected by a time-varied magnetic field. Using the magnetic micropillars, here we apply cyclic strain of some frequencies to a single osteoblast cell through focal adhesions and track cell migration with time-lapse observation to understand how the cell senses and responds to cyclic strain. Our data indicate that the cell may change the direction of migration to move away from the micropillar cyclically deflected in the frequency range from 0.1 to 50 Hz.

Topics: Osteoblasts
Commentary by Dr. Valentin Fuster
2015;():V003T03A103. doi:10.1115/IMECE2015-51456.

Mechanical stimulation induces new bone formation in vivo and promotes the metabolic activity and the gene expression of osteoblasts in vitro. It was reported that biochemical signals of osteoblasts to sense mechanical stimulation are activated according to their actin cytoskeletal deformation. However, there have been not so many researches on the relationship between cytoskeletal deformation and biochemical response. Here we show an original method to investigate a cell mechanosensing system and the quantitative relationship between the deformation of cytoskeletal structure and the change of intracellular calcium ion concentration as biochemical response in a living cell stimulated by a micropipette. Gene transfection of green fluorescent protein to osteoblastic cells enabled visualization of actin in cells. When local deformation was applied to a single osteoblastic cell by a micropipette, the displacement distribution of cytoskeletal structure in the whole cell was automatically obtained from the two images of the cell before and after deformation by using Kanade-Lucas-Tomasi (KLT) method. Intracellular calcium ion response to mechanical stimulation was measured as the spatial and temporal changes of intensity of Fura Red loaded to a cell. As a result, we obtained the quantitative relationship between structural deformation and biochemical response of a cell and found that the change of calcium ion concentration increases with increasing the displacement of actin cytoskeleton. It indicates that the deformation of actin cytoskeleton is highly related to the cell mechanosensing system.

Topics: Deformation
Commentary by Dr. Valentin Fuster
2015;():V003T03A104. doi:10.1115/IMECE2015-52641.

For efficient temperature control of the cooling device for medical purposes, accurate modeling of the focal cooling system taking into account the human physiological reaction and nonlinearity of the thermoerectric device, is required. In this paper, we examined about model parameters identification in order to establish a mathematical model for a focal cooling device for a living body using a Peltier device. Cooling experiments applied input constant voltage were performed to identify the model parameters. The temperature response data are obtained for every 0.1V, from 0.1V to 1.8V. As a result of the parameters identification, it was shown that some unknown parameters vary with a certain tendency to the input voltage. As a result of comparison between simulation value using identified parameters and experimental value, it was shown that one can simulate results in the error range of the parameter identification in the control surface.

Commentary by Dr. Valentin Fuster

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