An Investigation of Regional Variations in the Biaxial Mechanical Properties of Porcine Mitral Valve

Objective Mitral valve(MV)plays an importance role in regulating blood flow from left atrium to left ventricle and preventing backflow to left atrium.Mitral Valve consist of four important parts;anterior leaflet,posterior leaflet,chordae tendineae,and papillary muscles,which all work in harmony.The material properties alteration on the leaflet causes MV malfunction,and leading to valve diseases such as regurgitation and stenosis.The alteration may be caused by several factors such as calcification,genetic disorders,and infection,which usually have an influence to the mechanical properties,and thus affecting the mechanical behavior of MV.In consequence,some of the patients need MV replacement or repair to restore the normal function of MV.The important point for succeeding such a medical treatment depends on the technique,design,and material used in the treatment shall help rebuild the normal mechanical environment and behavior of MV.Therefore,the mechanical and materials characteristics of MV become a magnetism to explore.In this study,we present an integrated experimental and mathematical constitutive study base in collagen distribution aiming at the mechanical property differences in various region on MV.Methods and materials Both the size and composition of porcine valves are similar to human’s,so the porcine heart valve is often being used in experimental research.Mitral valve was isolated from fresh eight porcine hearts(250-500 gr),and perfused in PBS solution to maintain moist.Anterior and posterior leaflets were separated and dissected into 4 part(two 8~*8 mm rough zone and two clear zone samples)and 2 part(8~*8 mm belly and edge of the clear zone)respectively.Tracking markers(glass bean)were stickled on specimen with superglue(cyanoacrylate adhesive).Then,the specimen was mounted onto biaxial tester machine(CeIIScale,Biotester),and the tests are run by force control.During mechanical test,the specimen is immersed into PBS solution in physiological temperature(37℃).Every test procedure contains 8 preconditioning cycles and 8 loading cycles.The mechanical behavior was determined from the relationship between first Piola-Kirchoff stress and stretch.Constitutive model was reconstructed and material parameters were fitted from biaxial tensile result.Histological analyses were performed in the specimen before and after test.First,a piece of the specimen was cut and immersed in fixation solution(4%paraformaldehyde),then it was dehydrated in graded alcohol solution,and next embedding in paraffin wax block.Paraffin block was then cut and stained with VVG and Picro-sirius red.The collagen fibril orientation was observed from those histological results.Results The experimental results of the clear zone of MV’s first Piola-Kirchhoff stress and stretch curve are similar to those of the recent study from others,while result of the rough zone shows a different trend.This can be explained by differences in collagen distribution between clear zone and rough zone of MV.Our result thus allows for a refinement of computational models for more accurately predicting MV condition,where tissue heterogeneity plays an important role in the MV function.