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Mechanical Characterization of Preterm Neonate Pig Liver as a Function of High-Density Lipoprotein (HDL)

[+] Author Affiliations
Esra Roan, Alex Bada, Randy Buddington

University of Memphis, Memphis, TN

Paper No. IMECE2010-39363, pp. 705-711; 7 pages
doi:10.1115/IMECE2010-39363
From:
  • ASME 2010 International Mechanical Engineering Congress and Exposition
  • Volume 9: Mechanics of Solids, Structures and Fluids
  • Vancouver, British Columbia, Canada, November 12–18, 2010
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-4446-5
  • Copyright © 2010 by ASME

abstract

Elastography, a non-invasive imaging modality, utilizes mechanical properties of tissue as markers for disease diagnosis or staging. In the case of liver, there have been a number of studies focusing on the relationship between elastic mechanical properties and underlying disease, i.e. fibrosis and cirrhosis. In summary, these studies indicate the feasibility of elastographic tools in detecting liver diseases such as fibrosis and steatosis. There have not been any studies looking at the mechanical properties of the preterm neonate liver to date, which is important, because preterm neonates are at a greater risk for developing liver complications due to their aggressive dietary needs that are met with total parenteral nutrition (TPN). They use of elastography may be less from the use of elastographic tools since the concerns over noise levels in measurements resulting from abdominal wall thickness may be less influential. Therefore, it is necessary to establish basic preterm neonate liver mechanical properties. In this study, we measured the nonlinear (hyperelastic) mechanical properties of livers from preterm pigs that were fed common neaonatal diets, i.e. colostrum, total parenteral nutrition (TPN). 16 neonate pigs survived the feeding regime. Mechanical evaluation of 15 of these neonatal pigs was achieved with the use of uniaxial compression experiments at 0.01 s−1 strain rate. The livers averaging a weight of 34.7±7.0 (SD), were stored in phosphate buffered saline solution at 4°C until experimentation, which occurred within 30 minutes of the animal sacrifice. A minimum of three specimens from each liver was required for the computation of averaged mechanical properties. In addition to mechanical testing samples, blood serum was also obtained from these animals and common chemical parameters for liver health were measured (bilirubin, ALT, AST, HDL, LDL, etc.) Exponential form of the hyperelastic strain energy function, W = b1 exp[b2 (L2 + 2/L-3)], where bi are the material parameters and L is the stretch ratio, was utilized to describe the hyperelastic mechanical behavior of the preterm neonate pig livers. With the use of E = 6b1 b2 , a small-strain regime estimate of the elastic modulus of the neonate liver tissue was also computed. The mean b1 and b2 parameters are determined to be 97.00±44.15(SD) Pa and 1.90±0.28(SD) (n = 71). The mean elastic modulus exhibited an linear dependence on the HDL values obtained from chemical analysis of the blood serum. Moreover, although relatively weak, the ratio of the HDL over LDL also correlated with the elastic modulus. To our knowledge, this is the only study to date that has focused on the mechanical properties of preterm neonatal pigs and its correlation with liver lipid profile in neonates. Future work will focus on correlating this information with histology and then devising multi-scale material characterization approaches that link underlying neonatal liver structure to its overall mechanical properties.

Copyright © 2010 by ASME
Topics: Density , Liver

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