The development of circulatory prostheses, assist devices and artificial organs is a very active field. In this presentation, certain engineering design criteria for such blood wetted devices (termed Class III by the FDA) are discussed and illustrated with specific projects.

Many problems are observed when these devices are implanted into the cardiovascular system. The most common failure modes include hemolysis (rupture of the red blood cells), thrombosis (platelet activation and clot formation) and mechanical failure (wear, fracture, fatigue). These critical phenomena are highly dependent on the design and its influence of blood flow and material selection of the device. For example, it is now recognized that with mechanical devices hemolysis and platelet activation are mainly caused by exposure of the cells to high shear stress above certain thresholds. In that context, a new predictive model for hemolysis and thrombosis using the Wurzinger's empirical relations as state equations is proposed.

Flow visualization and computational techniques (FEA, CFD) are becoming important tools for the medical device designer. Furthermore, regulatory agencies (FDA, AAMI) are now integrating in their guidelines the use of these methods for the conceptual and development phases of the device. The medical industry has found its advantages in using these approaches in limiting the number of prototypes, trial testing and costly animal trials. We will discuss an approach to put in place such a methodology starting from the medical image data (IVUS, MRI) to generate anatomically correct models for simulating the different mechanical variables.