Glass-Ceramics of the Wollastonite - Tricalcium Phosphate-Silica System
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Mater. Res. Soc. Symp. Proc. Vol. 1243 © 2010 Materials Research Society
Glass-Ceramics of the Wollastonite - Tricalcium Phosphate-Silica System Jorge López-Cuevas, Martín I. Pech-Canul, Juan C. Rendón-Angeles, José L. Rodríguez-Galicia and Carlos A. Gutiérrez-Chavarría CINVESTAV-IPN Unidad Saltillo, Ramos Arizpe, 25900 Coah., México ABSTRACT Glass-ceramics based on hypo-eutectic (GC1) and hyper-eutectic (GC2) compositions of the Wollastonite (W, CaSiO3) - Tricalcium Phosphate [TCP, Ca3(PO4)2] binary system, which are saturated with SiO2 during the glass melting stage, are synthesized by the petrurgic method, using cooling rates of 0.5, 1 or 2°C/h. All synthesized materials are subjected to in vitro bioactivity tests using Kokubo’s Simulated Body Fluid (SBF). Primary α-Cristobalite is formed in all cases. Metastable Apatite [Ap, Ca10(PO4)6O] and W phases are additionally formed, in general, in the GC1 glass-ceramics, as well as in the GC2 material obtained at a cooling rate of 0.5°C/h. However, at faster cooling rates, TCP is formed instead of Ap phase in the latter composition. During the bioactivity tests, a hydroxyapatite [HAp, Ca10(PO4)6(OH)2]-like surface layer is formed in all materials. It is proposed that GC2 glass-ceramics cooled at a rate of 1°C/h have the potential to show good in vivo osseointegration properties. INTRODUCTION Over the last ten years, the eutectic composition (60wt% W-40wt% TCP) of the Wollastonite (W, CaSiO3) - Tricalcium Phosphate [TCP, Ca3(PO4)2] system, has attracted a great deal of attention in the field of biomaterials, mainly due to the development of the Bioeutectic® material [1,2]. This is the first designed bioceramic with the ability to develop an in situ interconnected porous hydroxyapatite [HAp, Ca10(PO4)6(OH)2]-like structure that mimics porous bone, in contact with physiological fluids, which confers to it excellent osseointegration properties. Its irregular lamellar eutectic microstructure, constituted by alternating radial lamellae of W and TCP phases, is obtained by slow solidification through the eutectic temperature (1402 ± 3°C) of the binary system. Thus, nucleation and growth of the W and TCP crystals occur during slow cooling from the molten state. This procedure is called “petrurgic method” [3,4]. When Bioeutectic® interacts with a physiological fluid, W is dissolved and TCP is pseudomorphically transformed into HAp-like phase, forming an interconnected porous structure. Lastly, a dense HAp-like layer is formed by precipitation on the outer surface of the material. The outstanding characteristics of Bioeutectic® seem to have inhibited the interest of the researchers to study non-eutectic compositions of the W-TCP system, which could be also useful as biomaterials. In the present work we synthesized, by using the petrurgic method, glassceramics based on hypo-eutectic and hyper-eutectic compositions of the W-TCP binary system, which are saturated with SiO2 during the glass melting stage. The in vitro bioactivity of all synthesized materials is evaluated. EXPERIMENT
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