40207_44 - COMPOSITE BIOMATERIALS S halaby W. S halaby and...

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COMPOSITE BIOMATERIALS 44 Shalaby W. Shalaby and Robert A. Latour 44.1 COMPOSITES AS A FAMILY OF BIOMATERIALS Although the use of high modulus metallic devices for internal bone fixation has been suc- cessful, there is a call to develop nonabsorbable, polymeric, composite substitutes having elas- tic modulus approaching or slightly higher than those of bones. This is to alleviate the problem of stress-shielding and consequent bone resorption as well as any concerns related to toxicity of metallic ions as corrosion prod- ucts. (Gillett et al., 1984; Tonino and Folmer, 1987). Furthermore, to avoid a second surgery to remove a non-absorbable device and to allow for gradual load transfer to healing bones, completely absorbable composites were proposed and evaluated by many investigators (Casper et al., 1985; Daniels et al., 1990; Lin, 1986; Tormala et al., 1991; Vainionpaa, 1987). Among the key types of totally absorbable composites are those based on polyesters or polyorthoesters, reinforced with organic fibers (Tormala et al., 1991; Vainionpaa et al., 1987) or calcium or sodium/calcium polymetaphos- phates (Casper 1985, Andriano et d., 1993). A family of composites having organic polyester fibers as fillers (e.g. poly-L-lactide reinforced with polyglycolide fibers, displayed large increases in strength and modest increases in stiffness (Tormala et al., 1991; Vainionpaa et al., 1987). On the other hand, polylactide reinforced with inorganic calcium Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 phosphate-based fiber showed large increases in both strength and stiffness (Casper et al., 1985; Lin, 1986). However, these families of composites lose a substantial fraction of their strength while retaining greater proportion of their stiffness after short term exposure to an aqueous physiological environment. Attempts to improve the strength retention have included coating the composite material to retard the transport of fluids to the polymer/fiber interface (Kelley et al., 1988; Andriano, Daniels and Heller, 1991) and sur- face modification of the phosphate fibers with a siloxane film barrier (Andriano, Daniels, and Heller, 1992). Growing interest in the inorganic phosphate-based fillers led Andriano and coworkers to compare the biocompatibility of several phosphate, fiber-reinforced polymers in a preliminary study (Andriano et al., 1993). Thus, phosphate fibers of calcium-sodium metaphosphate (CSM), sodium-calcium-alu- minum-polyphosphate (NCAP) and potassium metaphosphate (PMS), with copoly- mers E-caprolactone and lactide or polyorthoesters have been used as organic matrices. The CSM and NCAP fibers were found to be acutely nontoxic in cellular tissue and whole animal evaluation. 44.2 COMPOSITE BIOMATERIALS: GENERAL Like the more traditional composites, those classified as composite biomaterials contain two or more distinct constituent materials or phases on a microscopic or macroscopic size scale but not on the atomic level. Thus, fiber-
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958 Composite biomaterials glass-reinforced polymeric composites and other reinforced resins are composites while metal alloys are not. Interest in the former sys-
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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40207_44 - COMPOSITE BIOMATERIALS S halaby W. S halaby and...

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