Wollastonite - Tricalcium Phosphate Glass-Ceramics of Eutectic Composition Synthesized by the Glass-Crystallization Meth
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Wollastonite - Tricalcium Phosphate Glass-Ceramics of Eutectic Composition Synthesized by the Glass-Crystallization Method Jorge López-Cuevas, Martín I. Pech-Canul, Juan C. Rendón-Angeles, José L. Rodríguez-Galicia and Carlos A. Gutiérrez-Chavarría CINVESTAV Unidad Saltillo, Avenida Industria Metalúrgica No. 1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila, México, CP 25900 ABSTRACT Glass-ceramics of eutectic composition in the wollastonite [W, CaOSiO2]- tricalcium phosphate [TCP, β-Ca3(PO4)2] binary system were synthesized by using the glass-crystallization method. The parent glass was crystalized at 800-1300 °C for 0.5-5 h. The in vitro bioactivity of the synthesized glass-ceramics was tested in Kokubo’s Simulated Body Fluid (SBF) for 7-21 days, at pH = 7.4 and 37 ºC. All materials were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS). The results showed that metastable Apatite phase [Ap, Ca10(PO4)6O], plus W and TCP phases expected according to the binary phase diagram, were formed. Ap was the first phase formed at 900 °C/0.5 h, which was followed by formation of W phase at 900 °C/2 h and of TCP phase at 1200 °C/0.5 h. The relative proportion of the formed crystalline phases was a function of heat treatment temperature and time. A eutectic microstructure was obtained for the materials heat-treated at 1300 °C for 2 or 5 h. All glassceramics showed the formation of a hydroxyapatite (HAp)-like layer during the in vitro bioactivity tests. After 21 days of soaking in SBF, the samples treated at 1300 °C/5 h showed a behavior similar to that typically shown by Bioeutectic® material, while the materials heattreated at lower temperatures tended to form denser HAp-like layers, with similar thicknesses but with higher Ca/P molar ratios. INTRODUCTION Aiming to improve the osseointegration properties of the implant materials, as well as the bone-implant bonding, the use of materials with an appropriate porous interconnected structure has been recommended [1]. However, since porous materials commonly possess poor mechanical properties, P.N. De Aza et al. [2,3] designed a dense bioactive ceramic material capable of developing an in situ interconnected porous hydroxyapatite-like [HAp, Ca10(PO4)6(OH)2] structure that mimics porous bone, which was denominated as Bioeutectic®. This material has eutectic composition in the wollastonite [W, CaOSiO2]- tricalcium phosphate [TCP, β-Ca3(PO4)2] binary system (60% W - 40% TCP). It is usually synthesized using a procedure called “petrurgic method” [4,5], in which nucleation and growth of the W and TCP crystals occur during a slow cooling from the molten state. An alternative procedure that could be used for the synthesis of this kind of materials is the so-called “glass-crystallization method”, also known as “glass-ceramic method”. In this method, the first step consists in the preparation of a parent glass, which is crystallized later on by heat treatment. This method allows one to obtain materials with a wide span of phase composit
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