Design Of Biaxial Mechanical Properties Testing System For Mitral Valve And Study Of Valve Constitutive Equation

The mechanical properties of heart valves are the mechanical basis for structural analysis,calculation and design of prosthetic valves and tissue engineering valves.In this paper,a high precision biaxial tension system of heart valve was designed,and its stress-strain mechanical data were obtained by a biaxial tensile test of the valve tissue.In order to describe the relationship between valve stress and strain mechanics,this paper presents a constitutive model based on the theory of elastic mechanics and continuous medium mechanics,and compares it with the constitutive model proposed by other researchers.According to the data fitting results,it is proved that the constitutive model proposed in this paper can be more accurate for the mechanical properties of the valve.The main contents and results of this paper are as follows:First,according to the characteristics of valves,a biaxial tensile testing system for cardiac valves has been designed and developed.The system is programmed by LABVIEW language and provides a visual graphic programming method,which can easily connect the hardware equipment.The lower machine uses a stepping motor controller.Based on the NC programming language,the user controls the motion of the mechanical module,and the PCI6010 data collection card and the micro force sensor improve the mechanical signal.The accuracy of sampling,the collection of images from industrial cameras and the method of digital image processing based on MATLAB improve the accuracy of sample shape variables calculation.A program that can automatically identify the mark points on the image is compiled,which not only satisfies the accuracy requirement of sample shape variables,but also improves the work efficiency.This system is compared with the test data of high precision system abroad.The difference range of data contrast is 0.4%-3.4%.Next,based on the biaxial tension system,a double axis?circumferential and radial direction?tension test was carried out on the porcine mitral valve anterior flap.A number of experiments were conducted to explore the valve holding method and multiple valve tension tests were conducted.After a series of calculation and analysis,the mechanical stress-strain data of the valve tissue were obtained.Finally,the nonlinear an-isotropic viscoelasticity material of the mitral valve anterior valve was obtained.The circumferential stiffness was larger,the radial was more ductile,and the coupling of Circumferential and radial mechanics was obvious,and the stress relaxation was present.Finally,based on the stress-strain data of the mitral valve front flap,this paper presents a constitutive equation describing the mechanical properties of the valve tissue.The basic form is the strain energy function of the three order polynomial and the exponential term,W?28?c₁?I₁-?3³?10?c₂?I₁-?3²?10?c₃?I₁-?3?10?c₄?e^Q-?1and the phase of the mitral valve front valve is characterized by the transverse isotropy and hyper-elasticity mechanical properties based on the numerical analysis.The material parameters are closed.In order to verify the accuracy of the equation,the strain energy function,single exponential term strain energy function and one order polynomial and exponential strain energy function are used to fit the parameters of the same set of data,and the results of the three models are compared with the accuracy,and the correlation coefficient and the fitting are compared.The results show that the three polynomial plus exponential strain energy function proposed in this paper can more accurately characterize the mechanical characteristics of the anterior mitral valve.