Biaxial Test And Study Of Myocardial Mechanical Properties

The heart muscle is essential to keep the heart beating.The most common cause of death in humans is heart disease,such as diastolic heart failure.The pathophysiology of this disease is related to changes in the elastic components of myocardial tissue,so quantifying ventricular wall stress is important for understanding normal and pathological ventricular mechanical behavior.Currently,research is focused on the development of computational models and biomimetic materials to better understand and treat heart disease.This paper focuses on the following parts:(1)In this study,the pseudo-strain energy function of Humphrey was used to characterize the passive biaxial mechanical characteristics of left ventricular myocardium.In strain energy functions,the myocardium is assumed to be incompressible,pseudoelastic,and transversely isotropic.The nonlinear least square method was used to fit the parameters of the myocardium from the apex of the left ventricle to obtain the corresponding material parameters.This pseudo-strain energy function was found to fit biaxial mechanical data(r~2?0.98).In addition,considering the influence of the muscle fiber Angle on the actual force on the sample,the model was generalized.(2)Experiments were conducted to explore whether frozen storage had an impact on the mechanical properties of myocardial tissue.Biaxial mechanical properties of myocardial tissue before and after 48 hours of freezing were tested to study and analyze whether the parameters of samples before and after freezing were different in the direction of fibers and cross-fibers.The analyzed parameters include peak tensile ratio,preloading tensile ratio,mechanical tensile ratio,elastic modulus in high stress region,elastic modulus in low stress region,ductility index and anisotropy index.The main findings of this study include:(i)the change in tissue extensibility was not statistically significant,the fresh tissue was slightly harder than the frozen tissue,and the anisotropy was stronger;(ii)the difference in stress relaxation behavior between fresh tissue and frozen tissue was small,and the relaxation degree of frozen tissue was slightly decreased.The results showed that cryopreservation had no significant effect on the mechanical properties of the observed myocardial tissue.(3)To fully understand the mechanics of the heart,the biomechanical behavior of each layer of the heart needs to be quantified.In this paper,samples of myocardium and epicardium were obtained from the same left ventricle of pigs,and experiments of equibiaxial mechanics were carried out on them.By comparing the stress-strain relationship of myocardium and epicardium,it was found that:similar to most of the soft tissue,epicardium exhibits nonlinear material properties,hysteresis,anisotropy and is able to undertake obvious in-plane load.But its material behavior is markedly different from that of the myocardium.