Studies of biaxial mechanical properties and finite element modeling of skin

The mechanical properties of skin have been widely applied in the diagnosis of certain diseases, in the design of plastic surgeries and in the development of artificial skin. The objective of this dissertation is to conduct mechanical property studies of skin from two individual but potentially connected aspects. One is to determine the mechanical properties of the skin experimentally by biaxial tests, and the other is to use the finite element method to model the skin properties.; In this research, dynamic biaxial tests were performed on 16 pieces of abdominal skin specimen from rats. Typical biaxial stress-strain responses show that skin possesses anisotropy, nonlinearity and hysteresis. To describe the stress-strain relationship in forms of strain energy function, the material constants of each specimen were obtained and the results show a high correlation between theory and experiments.; Based on the experimental results, a finite element model of skin was built to model the skin's special properties including anisotropy and nonlinearity. This model was based on Arruda and Boyce's eight-chain model and Bischoff et al.'s finite element model of skin. The simulation results show that the isotropic, nonlinear eight-chain model could predict the skin's anisotropic and nonlinear responses to biaxial loading by the presence of an anisotropic prestress state. We also used this model to build a skin wound closure model and the results are comparable with other researchers' results for similar studies.; As a special application of the skin's mechanical properties, Rapamycin and steroids effects on wound healing were studied using a rat model. Eight groups of rats that received different combinations of Rapamycin and steroid after abdominal incision of the dermal and fascial layers were used in the study. The tensile strengths of the skin and muscle strips from treatment groups were compared with the specimens from the control group. The results show that high doses of Rapamycin prolonged wound healing and the addition of steroids had a synergistic effect on delayed muscle recovery, particularly in animals receiving high doses of Rapamycin. The results may provide practical guidelines for clinical studies.