Photoelastic Stress Analysis of Silastic Poppets in Prosthetic Heart Valves

Some prosthetic heart valves with Silastic ball poppets undergo degeneration and variance. The problem is avoided with metal poppets; however, their impact can damage the cloth coverings on the struts, resulting in distorted blood flow paths. Consequently, renewed interest in mild-cured Silastic poppets and inserts is developing. With photostress equipment, we analyzed two spherical poppet models to study poppet degeneration. The first analysis simulated the ring type of loading transmitted from the valve seat to the poppet, and the second analysis involved hydrostatic pressure loading and a detailed stress analysis to simulate cage confrontation. Results showed that regions of the poppet were susceptible to stress cycling with relatively large tensions below the upper surface but above the ring support. This same location could experience large compressive stress, depending on how the poppet was positioned during a seating stroke. Shear stresses near the valve support ring were at least four times the hydrostatic pressure load. Such subsurface stress cycling should play a role in the formation of internal fissures that surface and fracture the poppet.