In vitro bioactivity and biocompatibility behaviour of atmospheric plasma sprayed Indian clam seashell derived hydroxyapatite coating on Ti-alloy

Initially, various hydroxyapatite (HA) powders were derived from the Indian clam seashell by the hydrothermal reaction method with varying heating temperatures (700-1000 celcius). Further, the synthesized and agglomerated pure HA powders were sprayed on Ti-6Al-4 V (ELI) alloy to deposit different HA coatings through the atmo-spheric plasma spraying (APS) technique. In the current work, the in vitro bioactivity and biocompatibility properties of the fabricated HA coatings are examined to find the usefulness of such coated samples for biomedical applications. In the first test, the coatings are exposed to the simulated body fluid (SBF) for 1, 3, and 5 days of duration. The XRD (X-ray diffractometry) and FESEM (Field Emission Scanning Electron Microscopy) analyses of the treated HA coatings reveal the formation of apatite structure, which has grown with immersion time. The biocompatibility of the HA coatings is examined through MTT (3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide) assay analysis by using human osteosarcoma cell line (MG-63 cell). All the HA coatings are found to show improvement in cell density with an increase in incubation time from 1 to 5 days. From these tests, the seashell-derived HA coatings are found to be both bioactive and biocompatible in nature. The variation in biological properties observed among the HA coatings is due to their different microstructural features resulting from the melting and solidification behavior of the HA feedstocks. As the deposition param-eters are kept constant, the synthesis condition of HA powders, such as the reaction temperature, has played a key role in varying the phases and stoichiometry of the resulting coating. With the highest amount of metastable and near stoichiometric HA phase content, the HA-1000 coating has shown the maximum amount of cell pro-liferation and apatite growth among all. However, from the alkaline phosphatase (ALP) activity test, the HA-800 coating is found to show the maximum ALP expression level. This is attributed to the highest thickness of such coating resulting from the high deposition rate of HA-800 powder. Possibly, the high porosity of HA-800 coating has allowed a good amount of HA material to participate in the reaction process.