Development of seamless tri-leaflet valves.

In terms of their hydrodynamic characteristics at physiologically-relevant flows, the tri-leaflet valves show remarkable in vitro performance in comparison with similarly sized or even larger prosthetic valves. The ongoing in vivo studies confirmed the importance of adequate fluid mechanical design criteria, surface smoothness and rigorously clean fabrication procedures to minimize thrombo-embolic phenomena in the absence of anticoagulant therapies. Results from ongoing in vitro and in vivo durability studies suggest these are promising prostheses for valve replacement.

Effects of polymer surface molecular structure and force-field characteristics on blood interfacial phenomena.

To quantify the effects of major surface structural factors influencing interfacial reactions induced by polymers in native blood, model surfaces of solvent-cast films of two analogous poly(ether urethanes) and three homologous polyamides (nylon 4, 6/6, and 12) were exposed ex vivo to canine blood under the well-defined hemodynamic conditions of the Stagnation Point Flow Experiment. The selected surfaces allow for incremental changes in properties and were characterized by their "Composite Surface Free ENergy Function," gamma'S, which describes the surface force field as the sum of the mean dispersion (gammaSd) and polar (gammaSp) contributions and is computed from wettability spectra obtained with ultrapure diagnostic liquids. Blood interfacial effects were measured by the shear-limited diameter of the white cell circle formed around the stagnation point, the flow parameter at which symmetric aggregation occurred, and the surface-number density of platelets, [P s], remaining adherent under fixed conditions. At identical flows, within each group of polymers, both the WBC-circle diameter and [P s] scale with gamma Sp/gamma'S, implying that 1) only the magnitude but not the interaction mechanism varies as a function of incremental structural and surface changes, 2) the primary determinant of surface-induced effects is the polar force contribution, and 3) the magnitude of gamma'S is secondary if gammaSd/gamma'S is sufficiently great.

The intravascular magnetic suspension of a test device for in vivo hemocompatibility evaluation of biomaterials.

To advance hemocompatibility evaluation techniques, a new in vivo method has been developed for the dynamic testing of candidate biomaterials in suitably-sized experimental animals. One of the salient features this method is that the material to be evaluated constitutes the blood contact surface of a slender body of revolution which is coaxially suspended in a large canine vessel by electromagnetic forces only. The insertion site of the specimen is distal and downstream to the test region, reducing the influence of thrombotic tissue substances. These experimental conditions also insure that the only chronically exposed foreign surface is that of the test material, whose interactions with blood components are not affected by contact with the vessel intima. As demonstrated in simulated Circulation Model experiments, macroscopic thromboembolic phenomena induced by the test material can be continuously monitored. Preliminary in vivo trials have verified the validity of the underlying principles; the feasibility of the required surgical techniques, and the adequate performance of the suspension system.