End stage renal failure is treated principally by an extracorporeal dialysis device. Over 400,000 patients worldwide are maintained by such thrice weekly treatments. The evolution of the modern dialyzer has been greatly dependent on advances made in polymeric material science and while the modern dialysis unit has reached a high state of safety and efficiency, there is still room for improvements in the areas of improved biocompatibility, lower manufacturing costs, consistent and controllable membrane characteristics and a thermal sterilizable membrane. In the Phase I period it was shown that the polymer family based on polyalkylsulfones can be fabricated into membranes having properties equivalent to modern dialysis membranes while maintaining their superior biocompatibility.