Influence of heat treatment method on selected physicochemical and biological properties of fluoride-substituted calcium apatite.

Purpose: The synthesis of fluoridated apatite consists of several stages, among which the heat treatment has a significant impact on the physical and chemical properties. The present study aims to elucidate the influence of two different sintering methods on fluoride-substituted apatite properties. Methods: For this purpose, a two F-substituted apatites were produced by heat treatment in different ways called "rapid sintering" and "slow sintering". Physicochemical properties of the obtained materials were analyzed using infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, X-ray diffraction, and mercury intrusion porosimetry. Cytotoxicity of materials was assessed using MTT test. Results: Sintering conditions significantly influenced some porosity parameters of the materials. The samples subjected to "rapid sintering" showed a larger total pore area and mercury intrusion volume, while the samples subjected to "slow sintering" showed higher average pore diameter. Other porosity parameters did not differ significantly between the tested materials. The crystalline phases and chemical compositions of both materials were the same. Both materials appeared to be non-toxic since their extracts did not caused reduction in the viability of MC3T3-E1 cells compared to control cells and the results obtained were similar for both materials. Conclusions: Sintering is an important step in the apatite synthesis process. The way apatite is sintered is a factor that influences its physicochemical properties. The study performed on fluoride-substituted apatite showed that sintering conditions influenced some porosity parameters but had no effect on composition, chemical structure or crystalline phase. The cytotoxicity of both materials was at the same level, indicating that both were non-toxic.