The Chemical Processing of Silicates for Biological Applications - A Review
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THE CHEMICAL PROCESSING OF SILICATES FOR BIOLOGICAL APPLICATIONS - A REVIEW L. L. HENCH* AND JUNE WILSON** *Advanced Materials Research Center, University of Florida, One Progress Blvd., #14, Alachua, FL 32615 **Bioglass® Research Center, University of Florida, J413 J. Hillis Miller Health Center, Gainesville, FL 32610
ABSTRACT A new application area for sol-gel processing biomaterials and implant devices, is presented. The concepts of bioactive fixation of implants is reviewed. Conventional processing methods for bioactive materials are compared with low temperature chemical processing. Advantages of sol-gel processing include new bioactive compositional ranges of ultraporous CaO-P 2 0 5 Si0 2 biogel-glass powders. Clinical applications of bioactive implants are discussed.
INTRODUCTION The scientific understanding of chemical processing of ceramics, glasses, and composites has matured [1,2] and several applications have reached commercialization. Sol-gel processing is now successfully used for films, powders, fibers, and even for as-cast net shape precision optical components [1,2]. This paper reviews a new application area for sol-gel processing; biomaterials or prosthetic (implant) devices. These new materials take advantage of the intermediate ultraporous state of gel processing. As summarized in Fig. 1, the thermal processing schedule used has six processing steps which lead to ultraporous matrices, without going to the seventh, full densification stage. Stabilization temperatures of pure silica components used for optics range from 650°C to 1000C depending on pore size [2]. In contrast, the multicomponent biogel-glass systems are stabilized at lower temperatures of 400-600°C in order to avoid crystallization. As silica content of the biogel-glasses increases crystallization is suppressed and a broader range of stabilization treatments can be utilized (Fig. 1). In this paper the structural features of these porous gel systems and their potential applications are summarized. In addition, a brief review of the behavior of bioactive glass, glass-ceramic and ceramic implants is included to compare with the behavior of the new gel derived bioactive powders recently developed by Li et al. [3] and Whang et al [4].
Bioactive Ceramics Until the seventies, when the reality of the term "bioactive" applied to implant materials entered the consciousness and the literature of the field acceptable implant materials were those considered inert. There are, of course, no such materials. All materials elicit a response when implanted in tissues. There are four main types of material/tissue response [5,6]. 1) 2) 3)
If a material is toxic, surrounding tissue dies. If a material is not toxic but is resorbable the material is slowly replaced by tissues. If the material is not toxic but is also inactive (formerly termed inert) the material is isolated by a thin, nonadherant fibrous capsule.
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
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4)
If the material is not toxic but bioactive, the adjacent t
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