VAD BIOMER BLOOD SACS - MECHANICAL TESTS AND ULTRASTRUCTURAL OBSERVATIONS

Ventricular Assist Devices (VADs) are a support to the heart function and are used as bridge to transplantation for a brief period in patien ts awaiting a donor heart. They consist of two sacs with two artificia l valves that allow blood flow, the whole connected to a specific elec tronic equipment. This study examines the performance of a segmented-p olyurethane elastomer, namely Biomer, that has been extensively used t o manufacture pneumatically actuated VAD blood sacs. Specimens obtaine d from three VAD blood sacs explanted from three human patients and sp ecimens from one unimplanted blood sac were investigated for mechanica l performance of the material and for the changes it undergoes as a re sult of mechanical stress and interaction with the surrounding biologi cal environment. The application of tensile strength at break yielded no relevant differences between unimplanted and explanted specimens. B iomer exhibited a high elongation at break for both groups, with somew hat lower values for explanted specimens. SEM observations carried out on the inner surface-in contact with blood-of unstressed explanted sp ecimens showed no thrombotic deposits, calcifications, microbial conta mination or structural changes. The complementary broken surfaces of s tressed specimens showed a distinctive fracture pattern.