Bioactive behaviors of porous apatite- and wollastonite-containing glass-ceramic in two kinds of simulated body fluid
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Simulated body fluid (SBF) has been widely used for assessment of bioactivities of different materials. Those kinds of conventional SBF (C-SBF) have a higher Cl− concentration and a lower HCO3− concentration than those of human blood plasma. Therefore, a revised simulated body fluid (R-SBF), with ion concentrations including those of Cl− and HCO3− exactly equal to those of human plasma, was recently developed. Porous glass-ceramic was used as the testing material to evaluate the two kinds of SBF. Results showed that C-SBF is considered more active than R-SBF because the porous glass-ceramic had a higher apatite formation rate on its surface, while R-SBF is considered to simulate the human body fluid more precisely than C-SBF.
I. INTRODUCTION
Glass-ceramic, containing crystalline apatite and wollastonite in a MgO–CaO–SiO2–P2O5 glassy matrix has been developed by T. Kokubo and shows high bioactivity as well as high mechanical strength.1,2 It has been shown that this kind of apatite- and wollastonite-containing glass-ceramic (A-W GC) bonds to living bone in a short time3 and maintains high mechanical strength for a long period even under load-bearing conditions in a body environment.4,5 Porous implants are considered more favorable over dense implants due to the following reasons:6,7 (i) they not only have large surface area but also provide a three-dimensional framework for bone growth into the matrix of the implant; (ii) interconnected porosity acts like an organization of vascular canals, which ensure the blood and nutrition supply for the bone; and (iii) in clinical application, porous implants having rough surfaces are easier to handle than dense ones. It is known that, on implantation into bone defect, most bioactive materials first form an apatite layer on their surfaces and bond to and integrate with living bone through the apatite layer.8–11 Therefore, apatite formation is the first essential step for the artificial materials to bond to living bone. On the basis of these findings, if an artificial material can exhibit apatite-forming ability in vitro, it can be one of the candidates of the bioactive
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 2, Feb 2003
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materials that can bond to living bone in vivo. Conventional simulated body fluid (C-SBF) with ion concentrations almost equal to those of human blood plasma can evaluate the apatite-forming ability of materials in vitro and therefore has been widely used for assessment of bioactivities of different materials.12,13 Those kinds of C-SBF, with higher Cl− concentration and lower HCO3− concentration than those of human blood plasma, also cause higher Cl− concentration and lower HCO3− concentration in the newly formed apatite layer,14 as compared with those in bone apatite. To simulate the human body fluid more precisely, revised simulated body fluid (R-SBF) with ion concentrations including those of Cl− and HCO3− exactly equal to those of human
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