Polymers prostheses

D J Lyman, F J Fazzio, Synthetic Polymer Prosthesis Material, US Patent Office, Pat No 4 173 689,1979. 

R. L. Whalen, "Connective Tissue Response to Movement at the Prosthesis /Tissue Interface," in Biocompatib/e Polymers, Metals and Composites, Technomic Publishing Co., Lancaster, Pa., 1983. 

Siloxane-containing devices have also been used as contact lenses, tracheostomy vents, tracheal stents, antireflux cuffs, extracorporeal dialysis, ureteral stents, tibial cups, synovial fluids, toe joints, testes penile prosthesis, gluteal pads, hip implants, pacemakers, intra-aortic balloon pumps, heart valves, eustachian tubes, wrist joints, ear frames, finger joints, and in the construction of brain membranes. Almost all the siloxane polymers are based on various polydimethylsiloxanes. 

Interest in predicative testing extends not only to long periods of service but to relatively short time periods as well when biodegradability is concerned or in biocompatible systems in medical use whether it be in adhesion of bone or prosthesis or packaging is concerned, and in food additives when for example a species may be of consequence when present in the polymer and potentially extracted or present as a delicate flavor or color and absorbed by the maeromolecular system. 

The application of polymeric materials in medicine is a fairly specialized area with a wide range of specific applications and requirements. Although the total volume of polymers used in this application may be small compared to the annual production of polyethylene, for example, the total amount of money spent annually on prosthetic and biomedical devices exceeds 16 billion in the United States alone. These applications include over a million dentures, nearly a half billion dental fillings, about six million contact lenses, over a million replacement joints (hip, knee, finger, etc.), about a half million plastic surgery operations (breast prosthesis, facial reconstruction, etc.), over 25,000 heart valves, and 60,000 pacemaker implantations. In addition, over AO,000 patients are on hemodialysis units (artificial kidney) on a regular basis, and over 90,000 coronary bypass operations (often using synthetic polymers) are performed each year (]J. 

Dental Polymers. Every year nearly a half billion dental fillings are done, and over a million dentures are constructed. Most of the materials used in each of these cases are polymeric. In addition, over 300,000 dental implants are made each year with either ceramics or polymers (1). The majority of the dental fillings and dentures are made from various copolymers of methyl methacrylate with other acrylics, although some other polymers, such as polyurethanes, vinyl chloride-vinyl acetate-methacrylate copolymers, vulcanized rubber, and epoxies, have been used to some extent. One major problem is aesthetics—the prosthesis must look natural and not discolor (by photoinduction or staining) to any great extent. 

The first implanted synthetic polymeric biomaterial appears to be PMMA, which was used as a hip prosthesis in 1947 (see USP XVIII, The Pharmacopia of the USA, (18th Revision), US Pharmacopoeial Convention, Inc., Rockville, MD, 1 September 1980). Polyethylene, and then other polymers, were used as implants in the middle ear in the early 1950s, yielding good initial results, but local inflammation limited the use of these materials. 

Most total replacement joints consist of a metallic and a polymeric component, although alternative materials such as ceramics and carbon reinforced materials are currently being examined for this role. The life of a prosthesis is thus directly affected by the rate of penetration of the metallic component into the polymeric component and this has prompted considerable Interest in the subject of wear of polymers in the hostile environment of the body. 

Bioadhesion, i.e. biofihn formation resulting in a fouling surface, is required for biomaterial to be considered as a part of the body (e.g., orthopedic prosthesis, hard tissue) to enhance its incorporation and its biomechanical response. Examples are in the rebuilding of bones, recolonization, and hybrid implants composed of two parts, a synthetic one (with polymers as the mechanical sub-... 

For several years, Goodyear supplied their compounded polymer under the name of Hexsyn to various research centers namely, Monsanto Research Corporation ( ), Washington University ( 5), National Bureau of Standards ( 6), Cleveland Clinic (2.) and Thermoelectron Corporation ( 8), These institutions have research programs for physical testing of polymers for use in circulatory assist devices and for the development and evaluation of a cardiac prosthesis funded by the NHLB-NIH. 

Prosthesis—Materials—Congresses. 3. Polymers in medicine—Congresses. 

Bone cement functions as a grouting material consequently, its anchoring power depends on its ability to penetrate between bone trabeculae during the insertion of the prosthesis [Charnley, 1979]. Being a viscoelastic polymer, it has the ability to function as a shock absorber. It allows loads to be transmitted uniformly between the implant and bone, reducing locahzed high-contact stress. 

Several implants are commercially available for total or partial disk replacements. For instance, currently, two polymer-based cervical and two lumbar disk prostheses approved by the FDA are being widely used for disk replacement applications [103]. The first artificial disk (DePuy Inc.), approved by the FDA in 2004, was based on a hard-on-soft technology, which employed a CoCrMo alloy in conjunction with UHMWPE. Alternatively, ProDisc-C (Eigure 19.3b,i), approved in 2006 and 2007 for both lumbar and cervical replacements, respectively, was based on similar types of polymer composites. More recently, Medtronic developed Bryan prosthesis using titanium alloys and PU polymer (Figure 19.3b,ii) [104]. 

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