Effect of Sintering Process of HA/TCP Bioceramics on Microstructure, Dissolution, Cell Proliferation and Bone Ingrowth

The purpose of this study was to determine the effect of sintering conditions on microporosity of and cell proliferation and bone ingrowth on biphasic calcium phosphate (BCP) bioceramics. Discs were prepared from a calcium-deficient apatite preparation that upon sintering at 1050oC and above, results in a BCP with 60% hydroxyapatite (HA)/ 40% beta-tricalcium phosphate (β-TCP) ratio. The discs were divided into groups which were sintered under different conditions of heating rate (programmed vs. non-programmed) and temperature (1050°C vs. 1200°C). The discs were characterized in terms of composition (HA/β-TCP ratio), surface morphology, surface area, surface microporosity, per cent microporosity, and dissolution properties. The in vitro effect of sintering conditions on cell proliferation was determined using an established mouse fibroblast cell line (L929). Results demonstrated the following: (a) the HA/β-TCP ratio remained 60/40 regardless of sintering conditions; (b) the % microporosity, surface microporosity, surface area of the BCP and cell proliferation on the BCP significantly decreased with increasing sintering temperature, and (c) the extent of dissolution decreased with decreasing per cent microporosity. The in vivo study indicated no tissue adverse reaction and direct bone contact with the implant surface, confirming the biocompatibility of the BCP bioceramics. Resorption of the BCP and bone ingrowth was directly related to the sintering temperature: the higher the temperature, the lower the resorption and the bone ingrowth. Results of this study indicate that per cent microporosity of the BCP bioceramics affects its dissolution properties and cell response. The study demonstrates that optimum per cent microporosity elicits optimum cell response and should be considered to provide osteogenic/osteoinductive property to bioceramics.