Modeling the Effect of Temperature and Potential on the In Vitro Corrosion Performance of Biomedical Hydroxyapatite Coatings

CoCrMo biomedical alloys were coated with a hydroxyapatite layer to improve biocompatibility and in vitro corrosion performance. A fast electrodeposition process was completed in 5 minutes for the hydroxyapatite coating. Effect of the solution temperature and applied potential on the in vitro corrosion performance of the hydroxyapatite coatings was modeled by response surface methodology (RSM) coupled with central composite design (CCD). A 5-level-2-factor experimental plan designed by CCD was used; the experimental plan contained 13 coating experiments with a temperature range from 283 K to 347 K (10 °C to 74 °C) and potential range from −1.2 to −1.9 V. Corrosion potential (E _corr) of the coatings in a simulated body fluid solution was chosen as response for the model. Predicted and experimental values fitted well with an R ² value of 0.9481. Response surface plots of the impedance and polarization resistance (R _P) were investigated. Optimized parameters for electrodeposition of hydroxyapatite were determined by RSM as solution temperature of 305.48 K (32.33 °C) and potential of −1.55 V. Hydroxyapatite coatings fabricated at optimized parameters showed excellent crystal formation and high in vitro corrosion resistance.