A Symposium Overview: Surface Properties of Implant Materials
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ABSTRACT Like most thriving human endeavors, the field of implant materials and devices intersects with a universe of populations and professions. Nearly everyone will "get into the act" in one way or another, resulting in a variety of perspectives that have more, or less, foundation in fact and genuine concern for the patient. Even the scope of the points of view of scientists and engineers is relatively broad. One reason for the richness of the field in which we work is the increasing number of sites in the body to which implants are being delivered for the treatment of disease and replacement or augmentation of natural tissues. Another reason is the diversity of materials used in implants and diagnostic devices. INTRODUCTION A wide range of materials currently is in use for biomedical and dental implants. All major classes of engineering materials are represented (metals and metal alloys, ceramics, composites, and polymers), as well as fluids (e.g. artificial blood, ophthalmologic gel) and "natural" materials (e.g. preserved tissues). Surface treatments are becoming more common in the manufacture of implants, taking advantage of bulk mechanical properties of one material and preferable interfacial properties of another. Recent events, such as the withdrawal of some commodity materials used in medical implants from the marketplace,' demonstrate the need for improved understanding of bio/material interactions and specification of material properties --in the finished device --- that ensure good implant performance. Better definition of both bulk and surface properties of devices is essential; this paper focuses on the latter. Surface properties of implant materials must be specified in relation to the intended use of the devices that incorporate them. Device design plays a key role. Expanded-PTFE vascular grafts rely on controlled cell adhesion and ingrowth for proper function; other vascular grafts are designed to avoid thrombosis. Implant duration, likelihood of resterilization, mechanical wear, and other factors also influence selection of materials and/or coatings and their surface characteristics. APPROACHING THE INTERFACE In the most general sense, the implantation of a device involves bringing "Part A" (the device) into contact with "Part B" (specialized tissue) in a highly reactive environment. Data from recipient systemic response and radiographic and magnetic resonance evaluations are very useful, but do not provide necessary details of bio/material adjustments early in the development and testing of an implanted device. To date, these details can be obtained only by removal of the device from the host system (cell culture, accelerated test environment, laboratory animal, or human subject), followed by carefully targeted analyses. Unfortunately, the opportunities to evaluate successful devices over the long-term, to confirm findings from in vitro and animal studies, are relatively few. Long-term studies are further impeded in the U.S. by the absence 3 Mat. Res. Soc. Symp. Proc. Vol. 414 01996 Materials R
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