The Influence Of Si On The Thermal Stability And Biological Performance Of Hydroxyapatite Ceramics

The paper includes generally two parts. First, the synthetical hydroxyapatite (HA) powder was mixed with silicon dioxide (SiO₂) power completely by mechanical mixing. The plates were sintered in an oven in the temperature of 1000-1200℃ in air to investigate the thermal stability of HA induced by SiO₂ and the biological evaluation of the samples. Then, silicon-apatite by chemical synthesis method were also studied in this paper. In the course of synthesizing HA, TEOS was added and incorporated with HA in the microcosmic level. The silicon-apatite was sintered in the temperature of 800-1100℃ to investigate the thermal stability of HA induced by Si.The phase components were analyzed by X-Ray Diffraction (XRD). The groups of OH^-, phosphate and silicate were analyzed by Fourier transform infrared spectroscopy (FT-IR). The weight loss and thermal analysis were done by Thermogravimetric-Differential Scanning Calorimeters (TG-DSC).The cell toxicity of SiO₂/HA were investigated by Lactic Acid Dehydrogenase (LDH).The cell proliferation and differentiation were investigated by Alamar Blue and Alkline Phosphatase (ALP). The cell distributing was observed by DAPI staining.The results indicate that HA begins to decompose at the temperature between 1000-1100℃ and completes the decomposition at 1200℃ with appearance of α-tricalcium phophate (a-TCP) stabilized by SiO₂ and tetracalcium phosphate (TTCP). During the decomposition process, SiO₂ kept unchanged and no silicate was found.In vitro, LDH results show that SiO₂/HA-1100 has the lowest cell toxicity;HA mixed by SiO₂ has better cell proliferation and differentiation ability than pure HA. Both the SiO₂/HA and the mixture of HA and SiO₂-stabilized a-TCP/TTCP have better bioactivity than the pure HA in the case of partially decomposition of HA. Inthe case of completely decomposition of HA, the bioactivity is lower because of the absence of HA. The results of DAPI were consist with the results of LDH, Alamar . Blue and ALP and proved that SiO2 enhanced the biological performance of HA.Silicon-apatite was synthesized by wet-chemistry method. The results show the Si-HA/TGP reduces the thermal stability of HA. Meanwhile, the thermal stability of Si-HA/TCP is lower than that of SiC^/HA in the case of the same Si content.