Electrochemical and structural characterisation of zirconia reinforced hydroxyapatite bioceramic sol–gel coatings on surgical grade 316L SS for biomedical applications

Yttria-stabilized zirconia (YSZ)/hydroxyapatite (HAP) composite coatings on surgical grade 316L stainless steel was carried out using sol–gel dip coating and calcination process. Various molar ratios of HAP and YSZ was developed, each YSZ/HAP gel coating showed an average particle size of ∼30 nm and the coatings were dried and calcined for crystallization. The functional group and crystallization characteristics of the coatings were analyzed using (FT-IR), X-ray diffraction (XRD) and energy dispersion X-ray analysis (EDXA). The formation of β-tricalcium phosphate (β-TCP) was controlled changing the Ca/P ratio in HAP phase and also YSZ content in the composite coatings. It was revealed that TCP content showed a very minimum value at Ca/P ratio of ∼1.67 and at YSZ content of 30 vol.%, respectively. The mechanism of increased β-TCP content with Ca/P ratio lower than 1.67 and increased YSZ content was explained as Ca-deficiency due to the Ca-diffusion into t-ZrO2 crystals to form a solid solution. The resultant coatings were analysed for its corrosion resistance through polarisation, impedance and ICP-AES analysis in simulated body fluid. The viability of the reinforced coatings were analysed by in vitro cell culture studies.