Polyurethanes blood pumps

One successful total artificial heart is ABIOMED s electric TAH. This artificial heart consists of two seamless blood pumps which assume the roles of the natural heart s two ventricles (Fig. 7). The pumps and valves are fabricated from a polyurethane, Angioflex. Small enough to fit the majority of the adult population, the heart s principal components are implanted in the cavity left by the removal of the diseased natural heart. A modest sized battery pack carried by the patient suppHes power to the drive system. Miniaturized electronics control the artificial heart which mns as smoothly and quietly as the natural heart. Once implanted, the total artificial heart performs the critical function of pumping blood to the entire body (6). 

Siloxane-urethane segmented copolymers, which have very good mechanical, fatigue and surface properties 370,377 or their blends with conventional polyurethane-(ureas) have been successfully used in the production of blood pumps, intra-aortic balloons and artificial hearts 200,332,370,376,377). 

Characteristics high flexibility and high impact resistance, and excellent biocompatibility. Film forms of polyurethane have been used in fabrication of vascular graft and patches, heart valve leaflets, blood pumps, diaphragms for implantable artificial heart, and carriers for drug delivery. Elastomeric fibers (Spandex) made from polyurethane copolymer have been used in surgical hoses. 

Polyurethanes, due in part to their flexibility and toughness, are perhaps the polymer of choice for ventricular assist devices and blood pumps. Consequently, they have received considerable interest as bloodcontacting materials. In nonhuman primates, those polyurethanes, such as Pellethane , which exhibit the most hydrophobic surface chemistry produce the least platelet consumption [12]. In dogs, early platelet interactions with polyurethanes vary considerably although relationships to polymer surface chemistry remain unclear [13]. Thus while polyurethanes are chemically versatile and possess many desirable mechanical properties, it is generally not possible to predict their biologic responses in humans. 

In this study, we have attempted to obtain a detailed, quantitative estimate of the surface chemical composition of two commercially available polyurethanes, i.e., Biomer and Avcothane, which have demonstrated a reasonable degree of blood compatibility. For example, Avcothane has been used as an intraaortic balloon pump for post-operative patients (5). Biomer also has been successfully used for artificial heart components in calves (14). 

Nyilas, the developer of Avcothane R, snythesized a copolymer of polyurethane and polydimethyl siloxaneW which is blood compatible and used in the making of heart assist balloon pump s. 

Segmented poly etherurethanes contain no water-soluble additives and are characterized by a high hydrolytic resistance, good processability, and good mechanical properties in comparison with otho elastomers. Therefore, polyurethanes of this type are widely used in medicine, for example as aortic balloon pumps, catheters, and housings for artificial hearts Thus, a corrdation betweaa blood compatibiUty and the chemical structure of polyurethanes has often been reported... 

Biolized materials have been used in our cardiac prostheses since 1969. The first application utilized glutaraldehyde treated bovine aortic valves in a Dacron fabric pump termed a "partially biolized heart". Since thick pseudoneointima (PNI) formation and calcification was observed, the Dacron covered surface was replaced with natural tissue material (9). This original totally biolized heart was a sac-type with a flexing element of natural rubber lined on the blood side with aldehyde treated bovine pericardium. The outside case of the device was made from polyurethane. Early in 1973, a calf implanted with this artificial heart lived for a then-remarkable seventeen days (10). Termination of the experiment was caused by a crack in the flexing sac. A passive implant of this device in the aorta did not show any thrombus formation during 5.5 years implantation. 

---