ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V03BT00A001. doi:10.1115/IMECE2013-NS3B.

This online compilation of papers from the ASME 2013 International Mechanical Engineering Congress and Exposition (IMECE2013) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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: Dynamics and Control in Biomechanical Systems

2013;():V03BT03A001. doi:10.1115/IMECE2013-62460.

The movement of embryonic cilia presents a crucial function in specifying left-right axis for vertebrates. Those mono-cilia are primary (9+0) cilia, whose characteristic architecture is based on a cylindrical arrangement of 9 microtubule doublets. Dynein motors located between adjacent doublets convert the chemical energy of ATP hydrolysis into mechanical work that induces doublet sliding. Passive components, such as the mediated cytoplasm, the ciliary membrane, and other possibly-existent structures constraint the ciliary motion and maintain the cilia structural integrity, thus resulting in the axonemal bending. Dynein motors located along microtubule doublets in a motile nodal cilium activate in a sequential manner. However, due to inherent difficulties, the dynein activation patterns in moving cilia can hardly be directly observed. The exact mechanism that controls ciliary motion is still unrevealed.

In this work, we present a protein-structure model reconstructed from transmission electron microscopy image set of a wide-type embryonic cilium to study the dynein-dependent ciliary motility. This model includes time accurate three-dimensional solid mechanics analysis of the sliding between adjacent microtubule doublets and their induced ciliary bending. As a conceptual test, the mathematical model provides a platform to investigate various assumptions of dynein activity, which facilitates us to evaluate their rationality and to propose the most possible dynein activation pattern. The proposed protein-trigger pattern can reproduce the rotation-like ciliary motion as observed by experiments. Further application of this approach to mutant cilia with ultrastructural modifications also shows consistency to experimental observations. This computational model based on solid mechanics analysis may improve our understandings regarding the protein-beating problems of cilia, and may guide and inspire further experimental investigations on this topic.

Topics: Proteins
Commentary by Dr. Valentin Fuster
2013;():V03BT03A002. doi:10.1115/IMECE2013-62696.

Vibrational dynamics of hand-held power tools are relevant for ergonomics and system performance. In application of these tools, the human user is in the force flow, thus has a relevant influence on the vibrations occurring in the human body. For development purpose and valid comparison between tools, reproducible testing is needed. The testing is most useful if it simulates different user types, working poses and muscle activation states, as observed in the tools’ application. The admittance of an anthropomorphic two link arm system strongly depends on the arm pose angles. This work examines how well this angle dependent behaviour can be approximated by a linear mass-spring-damper system, which is easier to build for test rigs. Parameter optimization under the assumption of fixed masses in the linear replacement system showed unsatisfactory fitting of the system dynamics for some arm poses. Therefore the authors recommend to consider building future test rigs in an anthropomorphic arm setup. The work further reveals the importance of implementing adjustable stiffness and damping in test rigs.

Topics: Testing
Commentary by Dr. Valentin Fuster
2013;():V03BT03A003. doi:10.1115/IMECE2013-63233.

Studies on unimpaired humans have demonstrated that the central nervous system employs internal representations of limb dynamics and intended movement trajectories for planning muscle activation during pointing and reaching tasks. However, when performing rhythmic movements, it has been hypothesized that a control scheme employing an autonomous oscillator — a simple feedback circuit lacking exogenous input — can maintain stable control. Here we investigate whether such simple control architectures that can realize rhythmic movement that we observe in experimental data. We asked subjects to perform rhythmic movements of the forearm while a robotic interface simulated inertial loading. Our protocol included unexpected increases in loading (catch trials) as a probe to reveal any systematic changes in frequency and amplitude. Our primary findings were that increased inertial loading resulted in reduced frequency of oscillations, and in some cases multiple frequencies. These results exhibit some agreement with an autonomous oscillator model, though other features are more consistent with feedforward planning of force. This investigation provides a theoretical and experimental framework to reveal basic computational elements for how the human motor system achieves skilled rhythmic movement.

Topics: Engines , Motors
Commentary by Dr. Valentin Fuster
2013;():V03BT03A004. doi:10.1115/IMECE2013-63300.

Newly developed miniature wireless inertial measurement units (IMUs) hold great promise for measuring and analyzing multibody system dynamics. This relatively inexpensive technology enables non-invasive motion tracking in broad applications, including human motion analysis. The second part of this two-part paper advances the use of an array of IMUs to estimate the joint reactions (forces and moments) in multibody systems via inverse dynamic modeling. In particular, this paper reports a benchmark experiment on a double-pendulum that reveals the accuracy of IMU-informed estimates of joint reactions. The estimated reactions are compared to those measured by high precision miniature (6 dof) load cells. Results from ten trials demonstrate that IMU-informed estimates of the three dimensional reaction forces remain within 5.0% RMS of the load cell measurements and with correlation coefficients greater than 0.95 on average. Similarly, the IMU-informed estimates of the three dimensional reaction moments remain within 5.9% RMS of the load cell measurements and with correlation coefficients greater than 0.88 on average. The sensitivity of these estimates to mass center location is discussed. Looking ahead, this benchmarking study supports the promising and broad use of this technology for estimating joint reactions in human motion applications.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A005. doi:10.1115/IMECE2013-63303.

The energetics of human motion has been intensely studied using experimental and theoretical methods. Knowing the kinetic energy of the human body, and its decomposition into the kinetic energies of the major body segments, has tremendous value in applications ranging from physical therapy, athlete training, soldier performance, worker health and safety, among other uses. Significant challenges thwart our ability to measure segmental kinetic energy in real (non-laboratory) environments such as in the home or workplace, or on the playing/training field. The aim of this research is to address these challenges by advancing the use of an array of miniaturized body-worn inertial measurement units (IMUs) for estimating segmental kinetic energy. As a step towards this goal, this study reports a benchmark experiment that demonstrates the accuracy of IMU-derived estimates of segmental kinetic energy. The study is conducted on a well-characterized mechanical system, a double pendulum that also serves as an apt model for the lower or upper extremities. A two-node IMU array is used to measure the kinematics of each segment as input to the segmental kinetic energy computations. The segments are also instrumented with two high-precision optical encoders that provide the truth data for kinetic energy. The segmental kinetic energies estimated using the IMU array remain within 3.5% and 3.9% of the kinetic energies measured by the optical encoders for the top and bottom segments, respectively, for the freely decaying pendulum oscillations considered. These promising results support the future development of body-worn IMU arrays for real-time estimates of segmental kinetic energy for health, sports and military applications.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A006. doi:10.1115/IMECE2013-64024.

Experimental data of wheelchair-users with varying levels of spinal-cord injury undergoing impact disturbances while seated in a wheelchair, was used to develop one degree-of-freedom rotational-link models of the wheelchair-users. A procedure based on the Maximum Likelihood estimation method was used to identify the parameters of the proposed models such as stiffness and damping coefficients. A good agreement between experimental and identified models responses was achieved. The proposed approach can be used to categorize the difference in response to vibration of patients with different levels of spinal-cord injury (SCI) and will eventually lead to the development of patient specific design criteria for wheelchair suspension.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A007. doi:10.1115/IMECE2013-64078.

This paper deals with nonlinear dynamics of deficient knees. A two dimensional model of the human knee to include tibia and femur, and the ligamentous structure between the two bones is used to investigate the nonlinear dynamics of the knee in order to differentiate between normal and deficient knees. An exercise in which the femur is pinned at the hip in a sitting position, and tibia in a vertical position is actuated by a vertical soft harmonic force at various frequencies is proposed. A significant difference between the behavior of normal knees and Anterior Cruciate Ligament (ACL), and Posterior Cruciate Ligament (PCL) deficient knees is predicted.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A008. doi:10.1115/IMECE2013-64204.

A tendon-driven articulated manipulator with disc-cam pulleys is presented for the kinematic modeling and the motion analysis of a human index finger. Using the proposed model as a foundation, the driving forces of the tendons of human finger could be further evaluated and compared with the estimation from the EMG signals. The motivation of using such a tendon-driven articulated manipulator model to emulate the structure and functionality of a human finger is initiated by the similarities between these two systems, where the joint motions of the systems are both activated by the force transmission of tendons either by the base-driven actuators or the contraction of human muscles. However, the distinction between these two systems is that the extension/flexion motion of a human finger is coupled with the abduction/adduction motion due to the anatomical complexity of the expansion hood of a human finger, while the motion of a general articulated manipulator is not coupled. Moreover, since the shapes of the base and head of phalanges are irregular, the joints of a human finger cannot be simply treated as a perfect revolute joint. Hence, for the motion compatibility between the human finger and the articulated manipulator, the functionality of the expansion hood and the tendon system of a human index finger are identified and the joints are treated as revolute joints with non-circular pulleys. Based on the kinematic model and motion simulation of the finger-alike tendon-driven articulated manipulator is accomplished, and the prototyping model of the manipulator is constructed. Motion comparison between the models with the constant and non-constant moment arms is also implemented.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A009. doi:10.1115/IMECE2013-64281.

In this study, we aimed to develop a computer-aided simulation technique to predict the axonal extension in the neuronal network evolution processes for design new scaffolds to activate the nerve cell and promote the nerve regeneration. We developed a mathematical model of axonal extension by using phase-field method and evaluated the validity of the mathematical model by comparison with the experiments. In the previous experimental studies, the peripheral nerve scaffold has been introduced to guide the axonal extension. Damaged part of nerve was replaced by the artificial tube as the scaffold to induce the axonal growth through the artificial tube and regenerate the nerve network. However, the scaffold made of biodegradable materials has a problem that it is degraded and absorbed before the nerve regenerate, and then the nerve cannot regenerate. Therefore, there is a need for the design and development of a scaffold for nerve regeneration to promote nerve regeneration. For that purpose, it is necessary to understand the difference between the axonal extensions by the surrounding environment, such as the shape or materials of the scaffold for nerve regeneration. In particular, the numerical technique to analyze the remodeling process of the nerve in the scaffold is strongly required to be established because the in-vivo experimental observation technology at the micro scale, bioethical issues in the animal experiment and requires time and money are also remained as unresolved problems. In this study, we developed a new simulation code which employed the phase-field method to predict the two-dimensional dendritic and axonal growth processes of nerve cells on cultivation scaffolds. We curried out the phase-field analyses to make clear how the parameters of Kobayashi–Warren–Carter (KWC) phase-field model affected on the morphologic growths of dendrite and axon. Simultaneously, we had observed the axonal extension process by using the PC-12D cells with nerve growth factor (NGF) on two-dimensional cultivation dish. Based on these axonal extension observation results, we approximated the morphological changes and establish the phenomenological model for phase-field analysis. Finally, we confirmed the validity of our newly developed phase-field simulation scheme in two dimensions by comparison with the experiments.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A010. doi:10.1115/IMECE2013-64289.

The articular cartilage and subchondral bone are modeled by using μ-CT and MPM measurement results for multi-physics analyses, which employed the conventional finite element code for the solid continuum and particle method — SPH — for the liquid continuum. The articular cartilage at the micro-scale consists of the chondrocyte, the extracellular matrix-collagen fiber, the proteoglycan and the intercellular fluid and modeled by using MPM observation results. The subchondral bone consists of the trabecular bone and the intercellular fluid, and these are modeled by using μ-CT measurement results. Both are remodeled by the cyclic stress caused by the joint movement such as walking and jogging. Especially, the flow of intercellular fluid causes the shear stress on the chondrocyte cell in the articular cartilage and on the bone cell in the trabecular bone. Therefore, the flow and stress analyses of both the articular cartilage and subchondral bone are strongly required. In this study, the multi-physics analyses combined with finite element and particle methods are carried out to investigate the stress stimulation on the chondrocyte cell and the surface of trabecular bone. For the solid phase analyses by using finite element code, the nonlinear viscoelastic constitutive model was introduced for collagen fiber, the elastic model for the trabecular bone. For the fluid phase analyses by using SPH code, the viscosity model was introduced for intercellular fluid.

Topics: Physics , Bone , Cartilage
Commentary by Dr. Valentin Fuster
2013;():V03BT03A011. doi:10.1115/IMECE2013-65064.

Wearable sensor systems have the potential to offer advancements in the study of motion disorders, particularly outside of a laboratory setting during activities of daily living or on a football field. Advantages like portability and the capability to gather real-world data have resulted in the rapid adoption of these sensors in various studies for gait analysis, balance control evaluation, physical activity recognition and fall prevention. However, before using wearable sensors in long-term acquisition studies, it is necessary to quantify and analyze errors and determine their sources. In this study, the accuracy of joint angles and velocities measured with the wearable inertial measurement unit (IMU) sensors were compared to both measurements from an optical motion-tracking system and from encoders on a robotic arm while it completed various predetermined paths. The robotic arm uses incremental encoders at each joint to measure and calculate its Cartesian motion relative to a reference frame using inverse kinematics. Motion profiles of the robotic arm were tracked using the onboard encoders, an eight-camera Vicon (Oxford, UK) motion-tracking system with passive retro-reflective markers, and four wearable IMUs by APDM (Portland, OR). In order to better isolate various types of contributing errors, linear, planar, and 3-dimensional robot motions were used. Data were collected from the sensors over several hours, which provided insight into time-based effects as well as management of large amounts of data for future long-term tracking applications. In addition, the authors have previously seen acquisition errors with high-speed gaits, thus robotic arm trajectories of varying velocities were used to provide further insight into these rate-based effects. Angular velocity and joint angles were compared for all three systems and used to investigate the hysteresis, drift and time-based effects on the IMUs as well as their accuracy during motion tracking. Effects on IMU performance due to the application of filtering algorithms were not investigated. The results show that the IMUs were able to calculate the joint angles within a clinically acceptable range of the gold standard optical motion-tracking system. The IMUs also provided accurate trajectory recognition and angular velocity measurements relative to the known motion input of the robotic arm. Future work will include the development of algorithms to detect gait abnormalities such as those seen in patients with mild traumatic brain injury (mTBI). To complement human subject testing with gait pathology, controlled introduction of gait deviations into this robotic testing framework will allow for well-characterized unit testing, providing more robust algorithm development.

Topics: Sensors , Robotics
Commentary by Dr. Valentin Fuster
2013;():V03BT03A012. doi:10.1115/IMECE2013-65282.

The work presented here details the modeling, fabrication, testing, and analysis of a dynamic eating utensil designed to reduce hand tremors in subjects with Parkinson’s disease. Most of the current work addressing this problem has been invasive, using medicine or electrical brain stimulation for example. Here, an analysis is presented on the nature of the tremor. This is then used to develop a multi degree-of-freedom analytic model for the forearm/wrist/utensil system. Experiments were performed to identify model form and parameters and theory is presented which allowed for optimized system design. A physical model of the hand/wrist system was developed for testing utensil prototypes in controlled experiment. Ultimately iterative human subject testing validated the design decisions, providing both hard data and survey results to shape the final product. In addition to general performance, special consideration is given to the engineering design parameters and those established by the candidates for ease of use. Specifically, the device presented here outperforms its predecessors in cost, manufacturability, and usability. Additionally, an option for easy user tuning makes the device appropriate for a large host of tremor sufferers. Quantitative and qualitative results indicating the overall effectiveness are presented with the design.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A013. doi:10.1115/IMECE2013-65609.

Increased knee valgus loading has been previously identified as a possible risk factor for non-contact anterior cruciate ligament (ACL) injury. Arm position during landing may affect the risk of injury by increasing the knee valgus load. The goal of this study was to examine the kinematics and kinetics of the knee joint during single-leg drop landings from platform heights that was subject specific. Ten subjects (5 female, 5 male) were selected to participate in this single-leg landing study. No significant difference in knee kinematics was noted between arm positions, or gender. Significant difference (p < 0.05) was noted in the varus/valgus knee angle at initial contact (VVIC) when comparing the 60% vertical max jump percentage (%VJMax) to the 80% VJMax and 100% VJMax.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A014. doi:10.1115/IMECE2013-65848.

We present a simple two-dimensional analytical model that estimates the knee joint loading during vertical ladder climbing. By developing a model with simplification assumptions, such as vertical ascent with no whole-body angular acceleration, we can grossly estimate knee loads under dynamic conditions using posture and whole-body acceleration. The model presented demonstrates that upward whole-body acceleration influences the knee load on the leading leg of the climber during ladder mounting and climbing.

In an effort to define the preferential departure acceleration during ladder ascent for use with the model presented, we also present preliminary data of the initial step onto a fixed ladder. These data are combined with the model at the moment of initial stance foot departure to generate preliminary knee loading estimates. Where appropriate and possible, the authors have attempted to compare and validate the analytical model with published knee loading.

Topics: Stress , Knee
Commentary by Dr. Valentin Fuster
2013;():V03BT03A015. doi:10.1115/IMECE2013-66039.

In this study, we focus on the problem of localizing an implant or a capsule device in the human body by a mobile sensor unit using distance measurements. As a particular distance measurement technique, time of flight (TOF) based approach involving ultra wide-band signals is used, noting the important effects of the medium characteristics for different organs and tissue. We propose a least-squares based adaptive algorithm with forgetting factor to estimate the 3-D location of an implant in the human body. After discussing convergence properties of the proposed localization algorithm, we perform simulations to analyze the transient characteristics of the proposed algorithm. Different white Gaussian noises are added to emulate the TOF measurement noises and environmental disturbances, and it is observed that the proposed algorithm is robust to such noises/disturbances. The algorithm is successful in keeping the estimation error at a very low admissible level.

Topics: Algorithms
Commentary by Dr. Valentin Fuster
2013;():V03BT03A016. doi:10.1115/IMECE2013-66071.

In this paper, we aim to model a functional task affected by injury, along with the corresponding neuromuscular compensation strategy, in order to understand differences in task performance during recovery from the injury. This study is motivated by differing rates of functional task improvements during recovery from anterior cruciate ligament repair. In particular, clinical studies have shown faster recovery times for single-limb forward hopping versus single-limb crossover hopping (hopping back and forth laterally while moving forward). Modeling this hopping task will help us understand whether the main factor of the differing functional results is from the physical restrictions of the injury, the compensation strategies used to overcome these restrictions, or a combination of both. Our hypothesis is that the discrepancies in clinical functional results will be reproduced by employing a feedforward compensation strategy, where the compensation is learned and adjusted over time.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A017. doi:10.1115/IMECE2013-66111.

This paper deals with nonlinear dynamics of deficient knees. A two dimensional model of the human knee to include tibia and femur, and the ligamentous structure between the two bones has been developed. The aim of this paper is to use nonlinear dynamics to differentiate between normal and deficient knees. An exercise in which the femur is fixed in a sitting position, and tibia is actuated by an anterior-posterior soft harmonic force at various frequencies is proposed. The results clearly show a significant difference between the behavior of normal knees and Anterior Cruciate Ligament (ACL), and Posterior Cruciate Ligament (PCL) deficient knees.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A018. doi:10.1115/IMECE2013-66353.

Linear PID and nonlinear sliding mode controllers are developed and applied to a spherical model of a contrast agent microbubble that describes its radial response to ultrasound input. The plant model is a compressible form of the Rayleigh-Plesset equation combined with a thin-shell model. A nonlinear control law for the second-order plant model is developed and used to design and simulate the sliding mode controller and is compared to the performance of a fixed-gain PID controller. The performance of the nonlinear controller on the contrast agent response is evaluated for various control scenarios. This work shows the feasibility of using a nonlinear control system to modulate the dynamic response of ultrasound contrast agents, and highlights the need for improved feedback mechanisms and control input methods. Applications of the nonlinear control system in this work include bubble radius stabilization in the presence of an acoustic wave, radial bubble growth and subsequent collapse, and periodic radial oscillation response while a bubble is within an acoustic forcing regime known to cause a chaotic response.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Innovations in Processing, Characterization and Applications of Bioengineered Materials

2013;():V03BT03A019. doi:10.1115/IMECE2013-62265.

In this work, we apply an image segmentation technique that uses pulse coupled neural networks to automatically discern the micro-features of cortical bone histology. In order to properly identify them, we exploit the geometric attributes of these micro features namely shape (i.e., circular or elliptical). These micro-constituent attributes are used as targets for the fitness function of the optimization method (particle swarm optimization, PSO) that was combined with PCNN along with an adaptive threshold, (T) that finds the best value for T between two segmented regions. The result is an optimal set of PCNN parameters that was found in this work to yield good-quality segmented pulses of the various micro-features of 2 different cortical bone images.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A020. doi:10.1115/IMECE2013-63106.

Tooth reconstruction materials are used to reconstruct damaged teeth as well as to recover their functions. In this study, the mechanical properties of various tooth reconstruction materials were determined using test specimens of identical shape and dimension under the same compressive test condition; the hardness values of them were obtained from previous studies and compared with those of enamel and dentin.

Amalgam, dental ceramic, dental gold alloy, dental resin, zirconia and titanium were processed as tooth reconstruction material specimens. For each material, 10 specimens having a of 3.0 × 1.2 × 1.2 mm (length × width × height) were used.

The stresses, strains, and elastic moduli of amalgam, dental ceramic, gold alloy, dental resin, zirconia, and titanium alloy were obtained from the compressive test. The hardness values of amalgam, dental ceramic, gold alloy, dental resin, zirconia, and titanium alloy were obtained from the references [14–19].

And, the stresses, strains, elastic moduli, and the hardness values of enamel and dentin were obtained from the reference [13].

The mechanical role of enamel is to crush food and protect dentin because of its higher wear resistance, and that of dentin is to absorb bite forces because of its higher force resistance. Therefore, the hardness value should be prioritized for enamel replacement materials, and mechanical properties should be prioritized for dentin replacement materials. Therefore, zirconia and titanium alloy were considered suitable tooth reconstruction materials for replacing enamel, and gold alloy, zirconia, and titanium alloy were considered suitable tooth reconstruction materials for replacing dentin. However, owing to the excessive mechanical properties and hardness values of zirconia and titanium alloy, these may show poor biocompatibility with natural teeth.

Thus far, no tooth reconstruction material satisfies the requirements of having both a hardness value similar to that of enamel and mechanical properties similar to those of dentin.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A021. doi:10.1115/IMECE2013-64767.

The intervertebral disc is one of the body’s most vital structures. It provides support and enables six degree of freedom (6DOF) motions in the spine: flexion, extension, right and left lateral bending, compression, and axial rotation. When individuals suffer from degenerative disc disease, the nucleus pulposus deteriorates, causing a loss of articulation in the intervertebral disc. To address this problem, replacements for the nucleus pulposus can be used. The objective of this study was to evaluate a potential nucleus pulposus replacement consisting of a hydrogel polymer. The hydrogel was synthesized by physically cross-linking 95%-weight polyvinyl alcohol (PVA) and 5%-weight polyvinyl pyrrolidone (PVP). PVA and PVP were selected for the hydrogel implant due to the natural biocompatibility when the two are physically cross-linked. In order to evaluate the mechanical effectiveness of the hydrogel, a slider-crank mechanism was designed and constructed to create the 6DOF motions when interfaced with a Universal Mechanical Testing System. The viscoelastic properties of the polymer were obtained using a rheometer, which determined the elastic (G′) and viscous (G″) moduli of the PVA/PVP hydrogel polymer by calculating the complex shear modulus (G*) under low-frequency oscillating shear deformation. This allows for study of the viscoelastic performance of the isolated nucleus pulposus and hydrogel implant. The elastic modulus of the hydrogel was tested at parameters 5%, 10%, and 15% strain with results of 228.6 Pa, 988.8 Pa, and 1793 Pa, respectively. However, the elastic modulus tested for the natural bovine specimen at 5%, 10%, and 15% strain were 712.9 Pa, 522.1 Pa, and 363.3 Pa, respectively.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A022. doi:10.1115/IMECE2013-65580.

The development of hydroxyapatite (HA) scaffolds for tissue regeneration, particularly for bone regeneration, is an alternative to treat bone defects due to cancer, other diseases or trauma. Although the hydroxyapatite has been widely studied in the literature, there are still some disparities regarding its mechanical performance. This paper presents the analysis of the structural performance of hydroxyapatite scaffolds based on experimental tests and numerical simulations. HA scaffolds with variable porosity were fabricated by the water soluble polymer method, using the Poly Vinyl Alcohol (PVA) as pore former. These scaffolds were then characterized by scanning electronic microscopy (SEM), stereo microscope and X ray diffraction (XRD). Different porous structures models were considered and analyzed by the finite element method (FEM). Compressive tests were carried out and used to validate the proposed numerical models. Also a theoretical analysis based on the Gibson and Ashby [1] model was performed. Finally the experimental, numerical and theoretical results were compared and the results show that the proposed numerical and theoretical models can be used to predict, with adequate accuracy, the mechanical behavior of HA scaffolds for different porosity values.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A023. doi:10.1115/IMECE2013-66489.

Hydrogels are the promising classes of polymeric drug delivery systems with the controlled release rates. Among them, injectable thermosensitive hydrogels with transition temperature around the body temperature have been wildly considered. Chitosan is one of the most abundant natural polymers, and its biocompatibility and biodegradability makes it a favorable thermosensitive hydrogel that has been attracted much attention in biomedical field worldwide. In this work, a thermosensitive and injectable hydrogel was prepared using chitosan and β-glycerophosphate (β-GP) incorporated with an antibacterial drug (gentamycin). This drug loaded hydrogel is liquid at room temperature, and becomes more solidified gel when heated to the body temperature. Adding β-GP into chitosan and drug molecules and heating the overall solution makes the whole homogenous liquid into gel through a 3D network formation. The gelation time was found to be a function of temperature and concentration of β-GP. This thermosensitive chitosan based hydrogel system was characterized using FTIR and visual observation to determine the chemical structure and morphology. The results confirmed that chitosan/(β-GP) hydrogels could be a promising controlled-release drug delivery system for many deadly diseases.

Topics: Drugs , Hydrogels
Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Nanomaterials for Biomedical Applications

2013;():V03BT03A024. doi:10.1115/IMECE2013-62980.

The influence of different physical forms of substrates on fibroblast behavior was examined by comparing the following experimental and control groups: 1) glass coverslips, 2) poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) cast films, 3) electrospun PMMAEA nanofibers, 4) electrospun PMMAEA/collagen nanofibers, and 5) electrospun collagen. Cell adhesion, spreading and proliferation were compared on the different substrates. It was observed that fibroblasts on electrospun PMMAEA, PMMAEA-collagen, and collagen substrates spread more slowly after plating, and did not spread out to the extent observed for glass or PMMAEA films. Cells on electrospun fibers exhibited more filopodial-like structures and fewer stress fibers than the glass and PMMAEA film surfaces. Cell viability studies showed that although cells remained viable on all substrates, proliferation was faster on glass and PMMAEA films than on electrospun substrates. Overall, fibroblast behavior appeared to more closely resemble in vivo behavior on the electrospun nanofibers than on films or glass substrates.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A025. doi:10.1115/IMECE2013-64223.

An antibacterial and biocompatible scaffold for fibroblasts proliferation based on chitosan has been developed. Chitosan solution is electrospun into uniform fibers of 100–200 nm in diameter that mimic the extracellular matrix of human skin. The fibrous mats are successfully cross-linked to be stable in acidic solution, which can be used to treat acute wounds. The crosslinked fibrous mats display antibacterial properties toward Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. The mechanical properties of fibrous mats are shown to be comparable to native skin dermis which protects the skin wound.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A026. doi:10.1115/IMECE2013-64687.

Central retinal vein occlusion (CRVO) is a vascular disease characterized by thrombosis of the retinal veins that can eventually lead to ischemia. Ischemic CRVO can then cause macular degeneration and neovascular glaucoma causing partial to full blindness. In this study, we determined the feasibility of electrospinning tubular scaffolds for treating CRVO and vascular disease. Electrospinning was utilized to produce customizable scaffolds from nano-bers using collagen type I. Scaffolds were treated with glutaraldehyde, glycine, ethanol, UV light, and combinations of the treatments for the purpose cross-linking and to study their angiogenic effects. Structural properties of the scaffolds were analyzed with scanning electron micrsoscopy (SEM). Scaffolds were immobilized with human recombinant vascular endothelial growth factor (rhVEGF165) to investigate the drug-delivering abilities of the electrospun materials and as a method to produce vascularization. The chick chorioallantoic membrane (CAM) assay was used to examine the effects of VEGF immobilizations and to evaluate the feasibility of creating an anastomosis to treat CRVO. Collagen onplants (non-electrospun) and electrospun implants were made on day 10 of embryonic development. Findings show collagen loaded with rhVEGF165 had improved vasculature and pro-angiogenic properties. The present study suggests that collagen can immobilize and release growth factor, be electrospun to mimic the ultrastructure of native blood vessels, and holds promise for vascular tissue engineering.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A027. doi:10.1115/IMECE2013-65070.

In this paper, a three-dimensional dynamic model describing drug delivery and swelling behavior of polyelectrolyte gels was developed based on the Maxwell-Stefan equation and Bio-heat equation. COMSOL software was employed to simulate hydrogel swelling and the transportation of created automatically by COMSOL, and it had 78035 elements, which was unconcerned with the results. The results showed that Maxwell-Stefan equation and Bio-heat equation were suitable for modeling hydrogel behavior of swelling with temperature change. In addition, when temperature increased, the hydrogel swelling increased which also intensified drug release.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A028. doi:10.1115/IMECE2013-65269.

The presence of Cyclooxygenase-2 (COX-2) biomarker has been associated with the development of certain types of cancer such as breast cancer. Moreover, reliable quantification of COX-2 as an enzyme responsible for pain and inflammation is vital. Here we demonstrate the feasibility of sensitive COX-2 detection via integration of nanoporous polyaniline fibers on the microfabricated platform to develop a label-free biosensor. Highly porous polyaniline nanofibers were fabricated in different diameters and integrated on the interdigitated microelectrodes to develop electrochemical platforms. Characterization results revealed that the smaller diameter improved the sensitivity of the biosensor due to enhancement in the specific surface area. The developed biosensor was able to detect analyte as low as 0.1pg/mL with a large dynamic linear range of 10fg/mL to 1μg/mL. The fabricated sensor showed remarkable sensitivity towards COX-2 antigen suggesting the significant contribution of this nanofiber based platform to the enhanced sensitivity in COX-2 analyte detection.

Topics: Nanofibers
Commentary by Dr. Valentin Fuster
2013;():V03BT03A029. doi:10.1115/IMECE2013-66107.

Osteochondral tissue is composed of ordered and random biological nanostructures and can, in principal, be classified as a nanocomposite material. Thus, the objective of this research is to develop a novel biomimetic biphasic nanocomposite scaffold via a series of 3D fabricating techniques for osteochondral tissue regeneration. For this purpose, a highly porous Poly(caprolactone) (PCL) bone layer with bone morphogenetic protein-2 (BMP-2)-encapsulated Poly(dioxanone) (PDO) nanospheres and nanocrystalline hydroxyapatite was photocrosslinked to a Poly(ethylene glycol)-diacrylate (PEG-DA) cartilage layer containing transforming growth factor-β1 (TGF-β1)-encapsulated PLGA nanospheres. Novel tissue-specific growth factor-encapsulated nanospheres were efficiently fabricated via a wet co-axial electrospraying technique. Integration and porosity of the distinct layers was achieved via co-porogen leaching and ultraviolet (UV) photocrosslinking of water soluble poly(ethylene glycol) (PEG) and <150 um sodium chloride salt particles providing greater control over pore size and increased surface area. Our in vitro results showed significantly improved human bone marrow derived mesenchymal stem cells (hMSCs) adhesion and differentiation in bone and cartilage layers, respectively. In addition, we are working on developing a novel table top stereolithography (SL) apparatus for the manufacture of custom designed 3D biomimetic scaffolds with incorporated growth factor encapsulated nanospheres for osteochondral defect repair. Our early-stage SL development has illustrated good corroboration between computer-aided design (CAD) and manufactured constructs with controlled geometry. The ultimate goal of the novel tabletop SL system is the manufacture of patient-specific implantable 3D nanocomposite scaffolds for osteochondral defect repair. The current SL system developed in our lab allows for efficient photocrosslinking of two novel nanocomposite polymeric materials for the manufacture of three-dimensional (3D) osteochondral constructs with good spatiotemporal control of growth factor release in addition to exhibiting similar mechanical properties to that of the native tissues being addressed.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Transport Phenomena in Biomedical Applications

2013;():V03BT03A030. doi:10.1115/IMECE2013-62307.

Dense particle-suspension flows in which particle-particle interactions are a dominant feature encompass a diverse range of industrial and geophysical contexts, e.g., slurry pipeline, fluidized beds, debris flows, sediment transport, etc. The one-way dispersed phase model (DPM), i.e., the conventional one-way coupling Euler-Lagrange method is not suitable for dense fluid-particle flows [1]. The reason is that such commercial CFD-software does not consider the contact between the fluid, particles and wall surfaces with respect to particle inertia and material properties. Hence, two-way coupling of the Dense Dispersed Phase Model (DDPM) combined with the Discrete Element Method (DEM) has been introduced into the commercial CFD software via in-house codes. As a result, more comprehensive and robust computational models based on the DDPM-DEM method have been developed, which can accurately predict the dynamics of dense particle suspensions.

Focusing on the interaction forces between particles and the combination of discrete and continuum phases, inhaled aerosol transport and deposition in the idealized tracheobronchial airways [2] was simulated and analyzed, generating more physical insight. In addition, it allows for comparisons between different numerical methods, i.e., the classical one-way Euler-Lagrange method, two-way Euler-Lagrange method, EL-ER method [3], and the present DDPM-DEM method, considering micron- and nano-particle transport and deposition in human lungs.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A031. doi:10.1115/IMECE2013-62430.

This paper develops a simplified analytical solution for the slow axonal transport of tau proteins. A six kinetic state model developed in Jung and Brown [1] was used to simulate transport of tau. The model was extended by accounting for tau degradation and diffusion in the off-track kinetic states. The analytical solution was obtained by assuming that transitions between anterograde and retrograde states are infrequent. This assumption was validated through an analysis of the sensitivity of the solution to changes in the values of the two kinetic constants that describe the transition rates between the anterograde and retrograde states, and by a comparison with the experimentally measured tau distributions reported in Konzack et al. [2]. The predicted average transport velocity of tau was also in the experimentally reported range.

Topics: Modeling , Proteins
Commentary by Dr. Valentin Fuster
2013;():V03BT03A032. doi:10.1115/IMECE2013-62461.

We develop a model for simulating prion transport in a tunneling nanotube (TNT). We simulate the situation when two cells, one of which is infected, are connected by a TNT. We consider two mechanisms of prion transport: lateral diffusion in the TNT membrane and active actin-dependent transport inside endocytic vesicles. Endocytic vesicles are propelled by myosin Va molecular motors. Since the transit time of prions through a TNT is short (several minutes), the two population model developed here assumes that there is no interchange between the two prion populations, and that partitioning between the prion populations is decided by prion loading at the TNT entrance. The split between the two prion populations at the TNT entrance is decided by the degree of loading, which indicates the portion of prions that enter a TNT in endocytic vesicles. An analytical solution describing prion concentrations and fluxes is obtained.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A033. doi:10.1115/IMECE2013-62549.

Wall-bounded separating and reattaching flows are encountered in biological applications dealing with blood flows through arteries and prosthetic devices. Separated and reattached flow regions have been associated in the past with the most common arterial disease, atherosclerosis. Previous studies suggest that local wall shear stress (WSS) patterns affect the location and progression rate of atherosclerotic lesions. A parametric study is performed to investigate the influence of hemorheology on the wall shear stress distribution in a separated and reattached flow region. Recent hemorheological studies quantified and emphasized the yield stress and shear-thinning non-Newtonian characteristics of unadulterated human blood. Numerical solutions to the governing equations that account for yield stress and shear-thinning rheological effects are obtained. A low WSS region is observed around the flow reattachment point while a peak WSS always exists close to the vortex center. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A034. doi:10.1115/IMECE2013-63360.

Radiofrequency ablation may be described as a thermal strategy to destroy tissue by increasing its temperature and causing irreversible cellular injury. Radiofrequency ablation is a relatively new modality which has found use in a wide range of medical applications and gained acceptance. RF ablation has been used to destroy tumors in the liver, prostate, breasts, lungs, kidneys, bones, and eyes. One of the early clinical applications was its use in treating supraventricular arrhythmias by selectively destroying cardiac tissue. Radiofrequency ablation has become established as the primary modality of transcatheter therapy for the treatment of symptomatic arrhythmias. Radiofrequency catheter ablation of cardiac arrhythmias was investigated using a finite-element based solution of the bioheat transfer equation. Spatial and temporal temperature profiles in the cardiac tissue were visualized.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A035. doi:10.1115/IMECE2013-63747.

Many theories and mathematical simulations have been proposed concerning urine concentrating mechanism (UCM). The WKM and region approach are the two most valuable methods for compensating the effect of tubule’s architecture in renal medulla. They both have tried to simulate tubule’s confinement within a particular region mathematically in one spatial dimension. In this study, continuity, momentum and species transport equations along with standard expressions for transtubular solutes and water transports on tubule’s membrane were solved numerically in three spatial dimensions which practically is the main significance of our novel approach. Model structure has been chosen as simple as possible to minimize the effect of other factors in tubule’s solute and water exchange. It has been tried to simulate the preferential interaction between tubules by introducing different diffusion coefficients for solutes in the intermediate media in order that changing this physical parameter directly could influence tubule’s confinement with respect to each other. The results have been discussed in detail and then the effect of solute’s diffusivity on UCM has been investigated subsequently. In overall, it has been found out that this simulation can validate the integrity of our proposed approach for further investigation in this field.

Topics: Kidney
Commentary by Dr. Valentin Fuster
2013;():V03BT03A036. doi:10.1115/IMECE2013-63916.

The Chandler loop is an artificial circulatory platform for in vitro hemodynamic experiments. In most experiments, the working fluid is subjected to a stress field via rotation of the Chandler loop, which, in turn, induces biochemical responses of the suspended cells. For very low rotation rates, the stress field can be approximated using laminar flow in a straight tube as a model. However, as the rotation rate increases, while still maintaining laminar flow, the effect of the tube curvature causes the stress field to deviate considerably from the straight tube approximation. In this manuscript, we investigate the flow and associated strain rate field of an incompressible Newtonian fluid in a Chandler loop as a function of the governing non-dimensional fluid dynamic parameters. We find that the Dean number, which is proportional to the rotation rate, is the dominant parameter in determining the fluid strain rate. We propose an empirical formula for predicting the average fluid strain rate magnitude in the working fluid that is valid over a wide parameter space to be used in lieu of the common, yet restrictive, straight tube-based prediction.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A037. doi:10.1115/IMECE2013-63940.

This paper describes visualization of thrombus formation process on orifice flows by laser sheet beam and normal illumination. The aim is to investigate the effects of shear stress or shear rate on the thrombus formation or thrombus formation rate. It was found that the white thrombus formation rate is proportional to square root of shear rate, and the white thrombus is dominant when the shear rate is more than 450 (1/s).

Commentary by Dr. Valentin Fuster
2013;():V03BT03A038. doi:10.1115/IMECE2013-64451.

The effect of the underlying blood vessel on the transient thermal response of the skin surface with and without a melanoma lesion is studied. A 3D computational model of the layers of the skin tissue with cancerous lesion was developed in COMSOL software package. Heat transfer in the skin layers and the lesion is governed by the Pennes bio-heat equation, while the blood vessel is modeled as fully developed pipe flow with constant heat transfer coefficient. The effect of various pertinent parameters, such as diameter of the blood vessel, lateral location of the blood vessel relative to the lesion, flow velocity of the blood, on the skin surface temperature distribution, have been studied in the paper. The results show significant influence of the underlying blood vessel on the temperature of the skin surface and lesion as well as on the surrounding healthy tissue. Thus, a need for development of evaluation criteria for detection of malignant lesions in the presence of blood vessels is is discussed.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A039. doi:10.1115/IMECE2013-64574.

Synthetic aperture particle image velocimetry is used with an excised human vocal fold model to study the airflow between the vocal folds during voice production. A whole field, time-resolved, 3D description of the flow is presented over multiple cycles of vocal fold oscillations. The 3D flow data are synchronized with a 3D reconstruction of the superior surface of the vocal folds and with the subglottal pressure signal.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A040. doi:10.1115/IMECE2013-64631.

Radiofrequency ablation is a medical procedure used to treat a variety of illnesses including liver carcinomas that cannot be treated by resection or radiological procedures. A multi-physics code was used to solve the Bio-heat Equation by a finite element methodology. The volume of coagulation necrosis caused by the heating of the tumor tissue as a function of perfusion rate was determined. A multi-needle probe deposited the RF energy into the tissue. Once the tissue was heated to greater than 50°C it was considered irreversibly damaged. Increasing perfusion rates reduced the size of the lesion. In order to heat a volume to a required temperature the time elapsed did increase.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A041. doi:10.1115/IMECE2013-65347.

Experimental data for the evaporation of micron-size, poly-disperse water droplets into air has been generated in order to validate a theoretical poly-disperse droplet evaporation model. The model considers air and droplets flowing along a tube and predicts changes in droplet sizes and temperatures as well as air temperature and humidity as functions of distance along the tube. There are small discrepancies between experimental and model results which can be explained in terms of the lack of mixing between the droplets and air stream and also possible settling of the larger droplets in the experimental apparatus.

Topics: Drops , Evaporation
Commentary by Dr. Valentin Fuster
2013;():V03BT03A042. doi:10.1115/IMECE2013-65406.

Mechanical properties of the cornea can be affected by diseases such as keratoconus. In keratoconus, a decrease in both thickness and rigidity of the cornea is observed. It is currently not clear whether and how changes in mechanical properties of the cornea are associated with corneal epithelial cell behavior.

In the present study, polyacrylamide (PAA) gels with different elastic moduli have been prepared and human corneal epithelial cells (HCECs) have been cultured on them. To investigate the effect that changes in elastic modulus may have on adhesion and migration of corneal epithelial cells, actin filament organization and expression of adhesion molecules were characterized. It was found that HCECs actin filament organization improves with increasing substrate stiffness and integrin α3 expression significantly increases on more compliant substrates.

Topics: Cornea
Commentary by Dr. Valentin Fuster
2013;():V03BT03A043. doi:10.1115/IMECE2013-66605.

As a minimally invasive physical therapy for targeted tumor treatment, cryosurgery is increasingly used in a wide variety of clinical situations such as for freezing ablation of skin cancers, glaucoma, lung tumor etc. owing to its outstanding virtues like quick, clean, relatively painless, good homeostasis, and satisfactory of little scar. A most important issue in performing such a surgical operation is to guarantee a strong enough freezing while minimizing the mechanical insertion trauma. Among the many freezing protocols ever developed, using a needle to deliver liquid nitrogen to the target tissues has been the most popular way to ablate the tumor. A critical need from the clinical aspect is that the size of the freezing needle should be as small as possible while supplying extremely large amount of cold to the target so as to take full use of the unique minimally invasive merit of the cryosurgery. This paper evaluated the freezing performance of different working fluids including liquid helium (He), liquid nitrogen (N2), alcohol (Alc), dichlorodifluoromethane (R12) and 1,1,1,2-Tetrafluoroethane (R134a). The freezing capabilities inside the biological tissues of several most promising coolant candidates were comparatively evaluated through the three-dimensional phase change bioheat transfer simulation. Future applications were suggested. It is expected that the present freezing strategy would offer new opportunities for realizing a better tumor cryosurgical ablation over existing coolants.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A044. doi:10.1115/IMECE2013-66606.

A mathematical model is presented for predicting magnetic targeting of multifunctional carrier particles that deliver therapeutic agents to malignant tissue in vivo. These particles consist of a nonmagnetic core material that contains embedded magnetic nanoparticles and therapeutic agents such as photodynamic sensitizers. For in vivo therapy, the particles are injected into the micro vascular system upstream from malignant tissue, and captured at the tumor using an applied magnetic field. In this paper, a mathematical model is developed for predicting noninvasive magnetic targeting of therapeutic carrier particles in a micro vessel. The flow of blood in the micro vessel is described by a two phase Herschel-Bulkley fluid model. The Brinkmann model is used to characterize the permeable nature of the inner wall of the micro-vessel. The fluidic force on the carrier traversing the micro-vessel and the magnetic force due to the external magnetic field is taken into account. The model enables rapid parametric analysis of magnetic targeting as a function of key variables including the size of the carrier particle, the properties and volume fraction of the imbedded magnetic nanoparticles, the properties of the magnet, the micro vessel and the permeability of the micro vessel.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A045. doi:10.1115/IMECE2013-66856.

A multiscale model of the neonatal Hypoplastic Left Heart syndrome (HLHS) circulation following the Hybrid Norwood procedure was used to obtain systemic and pulmonary perfusion rates as well as detailed hemodynamics in the aortic arch region. The effects varying degrees of aortic arch stenosis, an obstruction to flow through the mid aortic arch, were studied. Implementation of a 3.0mm and 4.mm reverse-BT shunt (RBTS), a synthetic bypass from the main pulmonary to the innominate artery, and its effects on local and global hemodynamics were also studied.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Vibration and Acoustics in Biomedical Applications

2013;():V03BT03A046. doi:10.1115/IMECE2013-62845.

Continuous Positive Air Pressure (CPAP) devices are used to generate pressurized airflow to relieve upper airways and allow Obstructive Sleep Apnea (OSA) patients to breathe comfortably and easily. The airflow path in these devices consists of several components including but is not limited to inlet and outlet ducts, a centrifugal fan, a humidifier and a human interface. These components contribute significantly to the noise generated by the airflow.

This research paper present a numerical study of a centrifugal fan performed with commercial ANSYS software package to predict the sound and vibration produced by the centrifugal fan. The methodologies are following: first, the unsteady flow field is computed using the CFD model to obtain aerodynamic quantities and sound sources. Then, the finite element method (FEM) is used to predict the flow-induced vibration using the predicted aerodynamic quantities. Finally, the Ffowcs-William and Hawkings’s (FW-H) acoustic analogy is used to predict the acoustic pressure at the far-field using the sound sources from the unsteady simulation.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A047. doi:10.1115/IMECE2013-63316.

Arterial blockages can occur in small or large arteries for a variety of reasons, such as obesity, stress, smoking and high cholesterol. This paper presents a feasibility study on a novel method to detect the behaviour of the blood pressure wave propagation for arteries in both healthy and diseased conditions in order to develop a relatively inexpensive method for early detection of arterial disease. The trend of this behaviour is correlated to the early development of the arterial blockage at various locations. Invasive sets of data (gathered from experiments performed on animals) are implemented into a 3D Computational Fluid Dynamic (CFD) model to determine how the arterial wall compliance changes when any abnormalities occur to the blood flow profile. At the same time, a 1D acoustical model is developed to transfer the information gathered (wave propagation for blood pressure, flow and arterial wall displacement) from the CFD model. Wave forms were collected at a location which was invasively accessible (the femoral artery). The computational and acoustical models are validated against the clinical trials and show good agreement. Any changes to the arterial wall displacement could be detected by systolic and diastolic blood pressure values at the femoral artery.

Topics: Acoustics
Commentary by Dr. Valentin Fuster
2013;():V03BT03A048. doi:10.1115/IMECE2013-63766.

Alterations in the structure and function of the pulmonary system that occur in disease or injury often give rise to measurable changes in lung sound production and transmission. A better understanding of sound transmission and how it is altered by injury and disease might improve interpretation of lung sound measurements, including new lung imaging modalities that are based on an array measurement of the acoustic field on the torso surface via contact sensors or are based on a 3-dimensional measurement of the acoustic field throughout the lungs and torso using magnetic resonance elastography. It is beneficial to develop a computational acoustic model that would accurately simulate generation, transmission and noninvasive measurement of sound and vibration within the pulmonary system and torso caused by both internal and external sources. In the present study, sound transmission in the airway tree and coupling to and transmission through the surrounding lung parenchymal tissue were investigated on a mechanical lung phantom with a built-in bifurcating airway tree through airway insonification. Sound transmission in the airway tree was studied by applying the Horsfield self-consistent model of asymmetric dichotomy for the bronchial tree. The acoustics of the bifurcating airway segments and lung phantom surface motion were measured by microphones and scanning laser Doppler vibrometty respectively. Finite element simulations of sound transmission in the lung phantom were performed. Good agreement was achieved between experiments and finite element simulations. This study validates the computational approach for sound transmission and provides insights for simulations on real lungs.

Topics: Sound , Lung , Phantoms
Commentary by Dr. Valentin Fuster
2013;():V03BT03A049. doi:10.1115/IMECE2013-64016.

Elastography techniques are being developed to diagnose and monitor the progression and treatment of diseases that correlate with changes in soft tissue stiffness. The objective of this paper is to outline the application of vibrations to the human cornea in order to reconstruct a stiffness map. Having a localized stiffness map is useful for early diagnosis of cornea related diseases such as glaucoma and keratoconus. Experimental data was collected by directly vibrating the excised cornea axisymetrically along the edge and measuring wave propagation inward with the use of laser vibrometry. Different methods have been implemented to increase the reflectivity of the cornea for laser vibrometry. To corroborate the data, as well as to test feasibility, experiments have been done on phantoms constructed from silicone-based polymers. To reconstruct the data into a stiffness map, an appropriate analytical model has to be derived. This paper outlines the derivation of the analytical model for the cornea starting with simple circular plates and moving towards the curved geometry of the cornea. To verify the analytical model, finite element simulations were used to replicate the results. These results have also been checked against experimental data to help determine any external variables that affect results. Overall, the feasibility and application of a process has been determined. Future goals include increasing in-vivo application to make the process safe and cost-effective.

Topics: Vibration , Cornea
Commentary by Dr. Valentin Fuster
2013;():V03BT03A050. doi:10.1115/IMECE2013-64641.

A standard knee-ankle-foot orthosis (KAFO) is typically prescribed to support the limb during locomotion, during which (KAFO) is used for people with isolated quadriceps weakness or paralysis. In this paper the measurement applied on girl undergoing palsy children in her left leg as a case study. The first pathological concern is of age, weight, length and the residual palsy limb of 30 years old, 59kg, 156 cm, and 76 cm respectively, while the second test done is on man suffering flexion knee and shorten left leg due to injection by a needle in a wrong position when he was a child. The pathological concern is of age, weight, length and the residual defect limb of 35years, 82kg, 172 cm, and 80 cm respectively. This work involves two major parts: the first of which is the experimental part to measure the ground reaction force for both healthy and intake legs. The interface pressure between leg and calf part is measured for twelve points covering the total KAFO surface area, while the vibration data (velocity, acceleration and frequency) are measured at the last stage for the patient at different positions during the gait cycle. The second part is the numerical part during which stresses is calculated using ANSYS software for two cases, the first one is calculating stresses due to IP loading condition, while the second is calculating stresses due to the harmonic and spectrum vibration type. The above procedures were used for two types of KAFO, the first one is for metal-metal KAFO type and the second is for the plastic-metal KAFO type. The result shows that the GRF for the healthy person limb is greater than that of the intake person limb in about (17 %) while the healthy limb has GRF lesser than that of the intake limb for the same person in (2.2%). The Maximum IP is recorded in the posterior regions in the thigh part with (51Kpa). The result shows that the maximum Vibration data is in the sensing position at the knee on (8.5 and 5.9)for acceleration and frequency respectively at knee region for the plastic-metal KAFO type. Using plastic-metal KAFO type also leads to reduce the vibration data on (6.4% and 26%) for both acceleration and frequency respectively at thigh region.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A051. doi:10.1115/IMECE2013-64681.

This paper describes a method by which broadband cyclic strain can be applied to focal adhesions of a cell. In recent years, evidence has been growing that focal adhesions act as mechanosensors of cells which convert mechanical force into biomechanical signaling. However, there are no effective methods by which mechanical stimulation with high frequency can be directly applied to each focal adhesion. Here we develop a micropillar substrate embedding micron-sized magnetic particles and enabling the micropillars to be deflected by external magnetic field. The combination of long and short micropillars produces the difference of deflection between them and enables the micropillars to apply strain to a cell. We verified that the micropillars responded to external magnetic field up to at least 25 Hz without phase difference. Using the magnetic micropillar substrate, we observed the cytoskeletal deformation of an osteoblast cell. The findings indicate that the present micro device can be used for investigating mechanosensing systems of a cell.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A052. doi:10.1115/IMECE2013-64893.

In recent years, reported concussions among American football players have attracted investigators attention as to the safety of the football helmet. This study investigates the effects of concussive impact forces on the brain of football players and the shock absorbing performance of actual football helmets. Initially, a lumped-mass analysis of the helmet and the head was carried out and then more detailed finite element models of the head and the helmet were analyzed. The results indicate that the acceleration and strain of the brain are both above the threshold of the concussion and that the current design of football helmet may not protect players against concussion.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A053. doi:10.1115/IMECE2013-65028.

The main driving mechanism during an asthma attack is the hyperconstriction of airway smooth muscle (ASM), which reduces the airway lumen and makes normal breathing difficult. The contraction can be relieved by using bronchodilator drugs such as Isoproterenol (ISO). This paper hypothesizes that superimposed length oscillations (SILO) may improve drug therapy when combined with ISO or used alone in asthmatic subjects. The aim of this study is to assess SILO patterns directly onto the airways of healthy and asthmatic subjects (mice), while they are under anaesthesia breathing spontaneously and pre-constricted (mimicking and asthmatic attack), and compared the response with the relaxation observed just with ISO.

Topics: Oscillations
Commentary by Dr. Valentin Fuster
2013;():V03BT03A054. doi:10.1115/IMECE2013-65435.

Patients who undergo inter-hospital transfer experience increased relative mortality, ranging from 10 to 100% higher than non-transferred patients. The high-cost, increased risk of complications and poor outcomes of transferred patients warrant the critical examination of potential causes. One of the major causes may be the external stressors that patients are exposed to during medical transport. To realize simultaneous measurements of external stressors, we developed a multi-sensor unit for measuring vibration, noise, ambient temperature, and barometric pressure. For preliminary evaluation, the sensor unit was tested on 29 medical transports, 11 air transports by a helicopter and 18 ground missions by an ambulance. The average whole-body vibration for each air and ground transport was calculated at 0.3510m/s2 and 0.5871m/s2 respectively. Air transports produced much higher level of noise than the ground transports. We found no significant difference between two modes in terms of average temperature and the temperature changes. Barometric pressure drops significantly during air transport, indicating potential use of this data for automatic mode classification.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A055. doi:10.1115/IMECE2013-65663.

Protein aggregation rate is known to be influenced by shear flow in protein solutions. This has important physiological implications as many of the body functions involve shear flow. Fluid mechanical shear can affect interactions between protein molecules, initiate protein aggregation, and further affect their biological activity. The shear rate is therefore an important parameter either to determine or to influence the properties of the protein solution when it forms a nucleus or aggregates. For experiments, the number density of nuclei can be controlled by using an optimal shear rate and protein concentration. However, this requires theoretical information on the shear rate for the experimental conditions. With this motivation, we have designed an experiment in which we can effectively apply shear with flow characteristics that can be calculated. Specifically, in a small hemispherically-shaped bowl, 4 mm in diameter we place the protein solution and insert a rounded rod that can be vibrated rotationally or laterally, maintaining spherical symmetry in the liquid region. This system is particularly useful when only small quantities of expensive protein solutions can be used for experimentation. We have carried out the mathematical analysis of the time-dependent flow field between two concentric hemispheres by the perturbation method using ε = U0/ωa ≪ 1 as a small parameter where U0 is a characteristic velocity, ω is the oscillation frequency and a is a length scale based on the vessel dimensions (bowl radius). We have obtained an analytical solution for the velocity field, and the shear rate in the liquid. In addition, with the nonlinear interaction of the oscillatory flow, there is a nonzero time-independent mean flow (known as streaming). With the integrated effect of shear in the liquid region, this result will be useful for conducting aggregation experiment in which the effective shear rate can be correlated to the aggregation rate.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A056. doi:10.1115/IMECE2013-65827.

Investigation of impact and stability effects on an artificial upper limb due to external disturbance is made and the findings analyzed. For this purpose an experimental rig was suggested and constructed. The experimental rig consists of a special impact hammer to simulate the disturbance occurred and a special measuring device (accelometer, power amplifier and two Chanel vibration analyzer). The vibration response of human was measured at different points along the hand by using specified selected points. A suitable finite element model using ANSYS14 was suggested and the results are compared with those obtained from experimental work. This study aims to investigate the effects of vibration and impact on upper prosthetic limbs and is also aimed at mitigating vibration to the human body for greater comfort of the amputee.

Topics: Stability , Vibration
Commentary by Dr. Valentin Fuster
2013;():V03BT03A057. doi:10.1115/IMECE2013-66098.

Tactile perception is a critical requirement for surgery procedures such as minimally invasive surgery (MIS). In this study, an acoustic wave tactile sensor array for force and shear modulus sensing was investigated. This device can sense the magnitude of the applied force change and the tissue’s shear modulus change by means of detecting an electrical impedance change. The 6×6 array with a pitch of 1.3 mm was fabricated using a face-shear mode PMN-PT piezoelectric resonator which is highly sensitive to acoustic impedance load. External forces (0–5 N) were applied to the sensor and the electric impedance shift was measured. The sensitivity was found to be 56.87 Ohm/N. Imaging test results for different force and load stiffnesses were also obtained. The proposed tactile sensing technique is also favorable for a number of other biomedical applications including haptic sensors for the robotic surgery and artificial skin or fingers.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Viscoelasticity of Biological Tissues and Ultrasound Applications Dynamics, and Control in Biomechanical Systems

2013;():V03BT03A058. doi:10.1115/IMECE2013-62268.

Knee cartilage is a soft tissue having viscoelastic properties. Under cyclic loadings, viscoelastic materials dissipate mechanical loadings through heat generation. In knee cartilage, this heat might not be convected because of the tissue avascularity, resulting thus to a local temperature increase. As cells are sensitive to temperature, these thermo-mechanical phenomena of energy dissipation could influence their metabolism. The goal of this study is to evaluate the effect of thermogenesis on chondrogenic differentiation. First, we focused our work in quantifying the heat generated in cartilage as a result to deformation. On a cellular level, the effect of thermal alterations on cell metabolism was assessed looking at the gene expression of transcription factors involved in chondrogenesis. Hence, human chondro-progenitor cells were cultured at 33°C and 37°C for 48 h and 96 h. An up-regulation in mRNA expression levels of Sox9 and its co-activator PGC-1α has been observed. These results point to a thermal contribution to chondrogenic gene expression.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A059. doi:10.1115/IMECE2013-64210.

Mechanical loading induces changes in the structure and function of soft tissue. Growth and remodeling results from the production and removal of constituents. We consider a tissue constituted of elastin and collagen. The collagen turns over at a much higher rate than elastin. In this work we propose a two-constituent, constrained mixture model for this soft tissue. One constituent is modeled as a viscoelastic material and the other as an elastic material. It is assumed that the collagen turns over depending on the stress applied and the elastin does not turn over. The standard mixture theory approach is followed and the balance equations are set-up. The model is studied in simple uni-axial loading to test its efficacy.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A060. doi:10.1115/IMECE2013-65596.

Viscoelastic Strain Response (ViSR) ultrasound is a novel acoustic radiation force (ARF)-based imaging method that noninvasively interrogates the viscoelastic properties of tissue by measuring the relaxation time constant for constant stress in the Voigt biomechanical model. The time constant is defined as the ratio of coefficient of viscosity to elastic modulus, so ViSR differentiates tissue with disparate viscosities and elasticities. ViSR ultrasound is performed by delivering two successive ARF impulses to a single region of exciation (ROE) and tracking the micrometer-scale displacements induced by the propagating longitudinal waves. ViSR does not rely on transverse wave propagation, which can be disrupted and difficult to track in heterogeneous and/or geometrically complex media. Another advantage to ViSR ultrasound is a large axial range relative to conventional ARF Impulse (ARFI) ultrasound.

In this overview, ViSR methods are discussed and demonstrated in calibrated viscoelastic tissue mimicking materials. ViSR ultrasound is then applied to differentiating fatty and fibrous deposition in muscle in a golden retriever muscular dystrophy (GRMD) dog model and in boys with Duchenne muscular dystrophy (DMD) with correlation to standard physical testing. ViSR is also applied to delineating the structure and composition of atherosclerotic plaques in a hypercholesterolemic pig model with histochemical validation. ViSR’s key advantages and disadvantages are discussed in regard to its general clinical utility.

Topics: Ultrasound
Commentary by Dr. Valentin Fuster
2013;():V03BT03A061. doi:10.1115/IMECE2013-66109.

The responses of soft tissue under acoustic radiation force excitations are used to image tissue mechanical properties for soft tissue discrimination and detection of breast tumors. The soft tissue viscoelasticy has been interrogated by step acoustic radiation force excitations. The corresponding induced time-dependent creep displacement is used to reconstruct soft tissue viscoelasticity or to estimate viscosity and elasticity contrast of the inclusion to background. The acoustic radiation force is highly localized in a small excitation region; and, one degree-of-freedom and homogenous assumptions are generally made to the analysis. However, these simplifying assumptions limit the accuracy of these methods. In this paper, a finite element model was built to demonstrate the effect of the dynamic response of viscoelastic heterogeneous soft tissue to step acoustic radiation force. Factors affecting the dynamic response of soft tissue were first investigated with the homogenous model, and the corresponding estimation quality based on the one degree-of-freedom model was evaluated. Then, the dynamic response of soft tissue with inclusion and different elasticity and viscocity for the tissue and the inclusion was studied. The results suggest that in order to improve the estimate of soft tissue viscoelasticity the heterogenenous nature of the tissue and its three dimensional geometry should be accounted in the model.

Commentary by Dr. Valentin Fuster
2013;():V03BT03A062. doi:10.1115/IMECE2013-66258.

The characteristics of human skin are easily changed by the states of the body because it is very sensitive to environmental transformation. And the development of the condition measurement technology of human skin is very important for improvement in QOL because it reflects body condition. Then, various devices for the condition measurement of human skin had been developed but there was no technique which can evaluate the skin by objective parameter easily.

In this paper, spherical indentation testing is studied to evaluate the dimension and rigidity of thin soft-tissues like human skin. Here, the Hertz contact theory is functionally expanded 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 Young’s modulus of the tissue 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 Young’s modulus of some thin materials. Furthermore, this technology is applied to the elasticity investigation of the human skin. Especially, the measurement results of elasticity characteristics of the skin of human face are shown as the first report. The influences of sex and ultraviolet rays and so on are discussed to reveal the mechanics of human skin in this report. Moreover, it is discussed about the validity of the device which measures the elasticity of the skin of human face.

Topics: Skin
Commentary by Dr. Valentin Fuster

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