Overview of Biomedical Materials
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TIN/SEPTEMBER1991
ide (EtO) sterilization. More generally, development is being driven by the need for new technologies that will allow a variety of devices to function more effectively. Meeting Cost-Cotttainment Demands One of the easiest, most effective ways to reduce the cost of a médical device is to use less expensive resins and polymers. Lower cost resins could find applications in blood oxygenator housings, syringe components, intravenous sets, and hemodialyzers, among other devices. However, function and biocompatibility must not be compromised. Another approach is to add value to médical devices that reduce the cost of médical care by reduced complications and hospital stay. If the rate of infections is reduced, for example, then the length of hospitalization drops and the use of drugs to treat infections is obviated. Examples of value-added devices that will function by incorporating new biomédical materials include thromboresistant coatings for cathéters, infection-résistant coatings for urinary cathéters, and percutaneous connectors that form a tight seal with the skin and therefore reduce infection, e.g., peritoneal dialysis, indwelling cathéters for cancer therapy, drivelines for the artificial heart, and vascular access for drug delivery or blood treatment, such as hemodialysis. Enhancing Product Design Some devices require new materials and technologies to function properly. For instance, new joint replacements with improved life spans are needed since current prostheses hâve a lifetime of only 10 to 15 years before failure. Improvements might include enhanced stress transfer to the bone, which can be achieved with designs that match each patient's bone shape, improved fixation to bone using bioactive
ceramic coatings, and the use of fiber composites which more closely match the mechanical properties of bone. New types of sophisticated médical devices increasingly require interdisciplinary teams to address their many and varied design requirements. Many devices demand a Systems approach, calling on the talents of biologists, materials scientists, mechanical engineers, chemists, and biomédical engineers. The design of a new small-diameter vascular graft for coronary artery applications demonstrates the diversity of requirements (Figure 1). Many design questions must be addressed, including graft compliance, dilation, dégradation, thromboresistance, infection résistance, calcification, biocompatibility, cytotoxicity, and leachability. Testing must also address other questions: What is the long-term chronic response? Will it cause tissues to thicken and eventually occlude the device? How will the patient's health and the drugs he takes affect the graft's overall response? Human factors issues for the surgeon include suturability, conformability, and ease of handling in the operating room environment. AU thèse issues must be considered in order to design a successful device. Other research and development involves artificial muscles using polymeric gels contained within a sac for contraction; microsurgi
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