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The hemocompatibility for the recently approved ventricular assist device EVAHEART(®) was examined through flow visualization with a 300 % scale-up model. The absence of flow separations around the centrifugal vanes indicated that the curvature of the open vanes was suitable. The flow in the vane-shaft clearance was found to effectively produce sufficient shear stresses along the stationary shaft surface. The hemocompatibility was verified for a wide range of flow conditions.

Low, stable friction, a higher load-carrying capacity, and lower leakage of sealed blood are required for mechanical seals in implantable ventricular assist devices. One solution is to apply surface texture to the mechanical seal surface, consisting of self-mated silicon carbide. However, the effect of surface texture on the frictional properties of mechanical seals under blood sealing conditions has not yet been studied. Therefore, this study aimed to clarify the effect of surface texture on fundamental frictional properties of mechanical seals and to propose design concepts for mechanical seals in ventricular assist devices. The results show that surface texture increases the critical load of mechanical seals, although it also causes periodic peaks in friction. Further, it was found that surface texture induces the formation of denatured protein aggregates on the sealing surface, also inducing periodic surface friction peaks. The frictional properties of the mechanical seals were stabilized by creating small, dispersed concave features with wet blast fabrication, followed by coating with diamond-like carbon. Lower and more stable frictional properties were thus achieved, while simultaneously ensuring a higher critical load.

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