采用瓣叶复合材料的生物心脏瓣膜的力学分析

采用微观组织结构分析及宏观复合材料分析结合的方法，分析了猪主动脉瓣的非线性复合材料性质，提出了一种适用于猪主动脉瓣的非线性复合材料本构模型，用提出的非线性复合材料本构模型，对闭合承载状态下的等厚度与变厚度几何模型的猪主动脉瓣的应力分布及变形进行了有限元数值模拟，发现：与各向同性瓣叶相比，单向增强复合材料的瓣叶不但具有较强的承载能力，而且具有较大的柔软性。

THE STRESS ANALYSIS BIOPROSTHETIC HEART VALVESLEAFLET COMPOSITES

The porcine aortic heart valve leaflet can be regarded as an elastic meshwork reinforced with stiff collagen bundles, showing an arrangement in circumferential direction; it's behavior is highly nonlinear anisotropic. Because the biaxial experiment of porcine aortic valve is very difficult, it is convenient if we can use the data of uniaxial experiment to analyze the porcine aortic heart valve leaflet including anisotropic behavior. This paper has analyzed the microstructure of leaflet by supposing a fibre-reinforced model of transversely isotropic materials. A nonlinear composite consitutive model is developed based on microstructure of leaflet and the linear constitutive model of the transversely isotropic materials. Because the ratio of longitudinal elastic modulus to transverse one is very large, we assume that the nonlinear longitudinal elastic modulus is only dependent on the longitudinal strain and the nonlinear transverse elastic modulus dependent on the effective strain in our nonlinear composite constitutive model. Using the nonlinear composites constitutive model obtained in this paper. the stress distri- butions and deformations of uniform and non-uniform thickness porcine aortic valves in closed phase and loaded condition are analyzed by 8-node super-parameter nonlinear shall finite element. The results show that: the location of the maximum stress of anisotropic leaflet is lower than the location of the maximum stress of isotropic leaflet, but both are nearly area of commissure edge which is the area of the calcification of leaslet observed in clinic. The stress distributions are very different between anisotropic and isotropic leaflets; Therefore it is necessary to consider the anisotropy of the porcine heart valve leaflet when the leaflet is analyzed. The longitudinal (circumferential) normal stress is considerably larger than the transverse (radial) normal stress of leaflet and the transverse (radial) deformation is greatly larger than longitudinal (circumferential) deformation of leaflet. So the fibre-reinforced structure of leaflet results in that the leaflet can bear larger load in circumferential direction whereas it is more fiexible in radial direction.