BIAXIAL MECHANICAL-BEHAVIOR OF EXCISED PORCINE MITRAL-VALVE LEAFLETS

Anterior and posterior leaflets from excised porcine mitral valves wer e mechanically tested under cyclic equibiaxial and strip biaxial stret ch protocols at a strain rate of 4-12%/s after preconditioning. Cauchy stress and Lagrangian strain were calculated for both membrane and th ree-dimensional cases. The leaflets exhibited nonlinearly elastic, ani sotropic behavior. Both anterior and posterior leaflets were less exte nsible in the circumferential than in the radial direction under equib iaxial stretch, with stress ratios of 5.7 and 4.3, respectively. The p osterior leaflets exhibited greater extensibility in both directions a nd lower circumferential posttransitional moduli (ranges 690-820 vs. 2 ,500-3,200 N/m for anterior). This larger posterior extensibility may be due to the greater number of chordal attachments, which provide add itional mechanical stability to this structure. Coupling of radial and circumferential mechanical behavior was evidenced by the response to different stretch protocols, indicating a complex microstructural coup ling between individual collagen fibers or bundles. These are the firs t biaxial data for mitral valves and are a foundation far the developm ent of a more detailed quantitative material description.