A variety of simple ceramic oxides were used in the pioneering studies of
bioceramics in the late 1960’s and early 1970’s. For example, Hulbert,et al. (1972)evaluated CaO • Al2O3, CaO • TiO2, and CaO • ZrO2 as both porous and non-porous implants in rabbit muscles and connective tissue for up to 9 months . Although such studies proved to be reasonably successful and helped to establish the basic understanding of the utility of ceramics in biomedicine and the role of porosity in their function, simple alumina ceramics generally performed better in implantation studies (Hulbert et al. 1982–83). By the end of the 1970’s, alumina had become the bioceramic of choice based on its combination of biocompatibility and strength. Later, the development of relatively high-fracture toughness zirconia ceramics led to their consideration as an alternative to alumina. Both alumina and zirconia are discussed in detail in the previous two
sections of this chapter.l ion release. In wear tests which produced over 100 ppb levels of metal ion release
HYDROXYAPATTTE
It is ironic that such an obvious candidate as hydroxyapatite did not come into fashion as a biomaterial for many years. , hydroxyapatite, Ca10(PO4)6(OH)2, is the primary mineral content of bone representing 43% by weight. It has the distinct physiochemical advantages of stability, inertness, and biocompatibility. The relatively low strength and toughness of hydroxyapatite, however, produced little interest among researchers when the focus of attention was on bulk structural samples. The now widespread and successful application of hydroxyapatite has largely been in a thin-film configuration. The thin, surface reactive coating has been applied to a variety of prosthetic implants, primarily for total hip replacement (de Lange and Donath 1989). These coatings have been plasma-sprayed on both Co-Cr and Ti-6Al-4V alloys. Optimal perfor mance has come from coating thicknesses on the order of 25–30 micrometers. Interfacial strengths between the implant and bone are as much as 5 to 7 times as great as with the uncoated specimens. The enhanced interfacial development corresponds
to the mineralization of bone directly onto the hydroxyapatite surface with no signs of intermediate, fibrous tissue layers. The substantial success of this coating system has led to its widespread use in total hip replacement prostheses. An example of an
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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