Fabrication, development and characterisation of calcium phosphate based bioceramic coatings on 316L stainless steel for biomedical applications

Hydroxyapatite (HAP) was synthesised by a precipitation method, using naturally available chicken eggshell (Ca source) and phosphoric acid (P source). The synthesised powder was electrophoretically deposited on 316L stainless steel (316L SS). The chemical composition of the synthesised powder was analysed. Ca was estimated by conventional EDTA titration and P by a gravimetric method. The Ca/P ratio was found to be 1.67, which resembles the stoichiometric HAP ratio. Fourier transform infrared (FT-IR) and powder X-ray diffraction (XRD) techniques were employed to confirm HAP formation. FT-IR spectra showed the characteristic peaks for phosphate and hydroxyl groups. The XRD results revealed that the major characteristic peaks of HAP appear in the regions of approximately 26 degrees, 28 degrees, 29 degrees, 30-35 degrees, 39 degrees, 46 degrees, 49 degrees and 50 degrees (2 theta) and also indicated that no impurities are formed during HAP formation. The in vitro evaluation of HAP coated 316L SS was performed in simulated body fluid (Ringer's solution) of pH 7.4 at 37 degrees C in a thermostatic water bath through cyclic polarisation, and the results indicated that the HAP coated 316L SS has better corrosion resistance than uncoated 316L SS.