Role of physical and chemical properties on gas transfer and blood compatibility of urethane membranes

A major limitation to long-term blood oxygenation is damage to blood elements. Interposition of a membrane between the gas and blood phases has helped but the thrombogenicity of the membrane material still limits the long-term use of blood oxygenators. This can result in microemboli, local thrombosis, degradation of gas transfer or the loss of certain blood elements such as platelets. Some copolyurethanes have been reported to have improved blood compatibility. This study was undertaken to explore the use of these new material for blood oxygenation. This involved the determination of the gas permeability coefficients of the copolyurethane materials. Also, the effects of molecular structure and fabrication variables on the gas permeability coefficients were studied. From these studies, it became apparent that to provide adequate gas transfrer, the copolyurethanes would have to be fabricated very thin or microporous. Thus, porous copolyurethane films were cast onto porous supports and their gas fluxes and surface compatibility assessed with flowing blood in a system simulating and artificial lung. Comparisons were made with presently used membrane materials including silicone rubber, Goretex® and Celgard®. The gas transfer of the porous copolyether urethane membranes was found to depend on the substrate used and the polymer coating thickness. When the thickness of the polymer coating was kept in the 3 to 5 µm range, gas transfer was adequate for blood oxygenation. The copolyurethane membrances were observed to have good blood compatibility as oxygenator membranes in that they absorbed fewer blood elements and had very few clots compared to the other material tested. This may be related to the finding that these materials absorbed more albumin and less fibrinogen than the other materials.