In our opinion, Micro-Renathane® is the most blood-compatible tubing ever made. This polyurethane based catheter tubing is exceptional for implantation studies in experimental animals. Offering extended catheter life this tubing reduces the probability of intravascular thrombosis. Scanning electron micrographs (approx. 10,000X) illustrate the dramatic difference between Renathane tubing and conventional vinyl tubing. After use in hemodialysis, Renathane showed significantly fewer surface deposits of platelets, proteins, trapped red cells and other blood elements than other tubings. "Medical Grade" Plastics - It is appropriate to clarify the definition of the phrases "medical grade" plastic and "FDA approved" plastic. There is no approved "medical grade" plastic or resin. Each individual supplier has his own criteria for what polymer and additive combinations constitute suitability for medical use. Similarly, there is no "FDA approved" plastic or resin in the Code of Federal Regulations. Food and Drugs, Title 21, Part 121, the FDA has listed the additives allowable in plastics intended for food contact use. In formulating a PVC compound for medical use the manufacturer generally chooses plasticizers, stabilizers, antioxidants, colorants, etc., which are acceptable for food use. Micro-Renathane® does not contain any plasticizers. Medical Uses of Polyurethane - Polyurethane based polymers were introduced into the United States from Germany. Early biomedical applications of polyurethanes were described by Boretos and Pierce. They reported excellent vascular acceptability in experimental heart-assist pump chambers and arterial cannulae. In subsequent work Boretos reported the absence of acute toxicity for segmented polyurethanes. He also reported that polyurethane rings did not deteriorate or cause tissue reaction after implantation for 18 months. Lyman and coworkers have also investigated polyurethanes for the fabrication of heart-assist devices. Artificial heart devices were constructed of this material and implanted in calves. Other uses of polyurethanes as biomaterials have been described by Bruck. Polyurethane based polymers are currently commercially employed in hollow fiber kidneys, vascular. catheters and intra-aortic balloons. Due to the slightly higher cost of polyurethanes, they have only been used where exceptional biologic and blood compatibility is required. Micro-Renathane® is sold only for experimental use in laboratory animals. A brief report, with references, is included with each shipment of Micro-Renathane®. We will be pleased to send a copy upon request.