In vitro evaluation of an oxygenator is an integral part of its development. In order to obtain meaningful data the test conditions must be standardised. The natural lung offers a large surface area for gas exchange and provides excellent oxygenation over wide range of blood flows. Consequently it should act as a good deoxygenator too. Our experience in using a sheep lung for deoxygenation is described.

The component materials used in fabrication of the Chitra heart valve, their choice and screening are described. Further the haemodynamic performance of this valve, which is under development and an equal sized No. 27 Bjork-Shiley valve prosthesis was compared in a left-heart pulse duplicator under similar conditions of flow rates and pressures. They were tested in both the aortic and mitral positions of the duplicator. Regurgitant volumes and transvalvular pressure gradients were measured over flow rates ranging from 2 to 8 LPM. Flow patterns of the fluid flow across the valves were also photographed. The results indicate that the performance of the indigeneous valve is comparable, if not marginally better, to that of the well-established Bjork-Shiley valve. Transvalvular gradients and regurgitant volumes were marginally lower for the Chitra valve. This is attributed to the improved design of the valve disc shape.

The interface between prosthetic materials and body tissues has become important thanks to the extensive use of bioimplants and artificial internal organs. The long-term function and survival of implanted prostheses depend on the stability of the material-tissue interface. The methods in current use for the fixation of implanted prostheses are mainly based on mechanical linkages which are inherently unstable. The manifestations of instability are seen in clinical phenomena such as prosthetic thrombosis and failure of skin-prosthetic linkage. A less vulnerable approach to stablising material-prosthetic interface would be the development of chemical bonding which has already been accomplished at the bone-bioglass ceramic level. The approach may have wider relevance to the linkage of polymeric materials to body tissues.

Hydrolysed poly(methyl methacrylate) microspheres with carboxyl residues distributed throughout the matrix were tested for their ability to support cell adhesion and growth. Cell growth as determined by protein content, phase contrast and scanning electron microscopy showed that these microspheres are growth-supportive. Further, preliminary experiments pointed to their usefulness in microcarrier culture.

The heart of a normal human being beats about 38 million cycles every year. An artificial heart valve, to perform at this rate in the adverse conditions inside the heart for 20 years or more, should be highly wear-resistant with excellent fatigue strength. Thus, the study of mechanical and physical properties of the materials intended for use in artificial valves becomes an inseparable part of the valve development process itself. The physical and mechanical requirements of the materials used in the Chitra heart valve have been evaluated by studying their water absorption, adhesive wear and abrasive properties. The mechanical durability of the device has been assessed by accelerated life cycle testing. The test systems developed for the above are described here. The results show UHMW-PE to be a highly wear-resistant material suitable for the occluder. The accelerated wear tests show that the valve with Haynes-25 alloy cage and UHMW-PE disc has durability in excess of 50 years.

Blood remains fluid so long as it flows in the cardiovascular system; it clots in other situations. While this phenomenon, vascular homeostasis, has been studied for a century, the development of artificial surfaces that induce minimal or no clotting became important only with the growth of cardiovascular surgery. The advent of the graphite-benzal konium-heparin surface which employed the ionic bonding of heparin was a milestone in the effort to develop non-clotting surfaces. The technique of ionic bonding was followed over the years by the grafting of heparin molecule to surfaces and most recently, by the covalent bonding of heparin. The covalent bonding of heparin preserves the non-clotting property of prosthetic surfaces for long periods and holds promise for numerous applications in cardiovascular surgery and other branches of medicine. The introduction of covalent bonding and similar approaches will greatly improve the biocompatibility and durability of the present generation of biomedical devices.