Influence of deposition temperature on the structure and functional properties of Mg doped hydroxyapatite coatings deposited on manufactured AZ31B alloy substrates by RF magnetron sputtering

In this paper, we study the effect of deposition temperature on the structural and nanomechanical properties on the degradation and bioactivity behaviour of Mg doped hydroxyapatite (HAP) deposited on AZ31B alloy substrates extracted by parts manufactured according to the prostheses production route. The coatings were prepared by RF (Radio Frequency) magnetron sputtering technique at room temperature (RT) and 200 °C, respectively. By adding Mg into the HAP matrix, the hardness and elastic modulus values of the coatings have significantly improved as compared to the bare HAP, the highest H3/E2 ratio of 0.022 being obtained for the HAP + Mg at 200 °C. XRD analysis showed the presence of an α-Mg hexagonal structure for the uncoated AZ31B alloy, while the GIXRD patterns revealed the presence of HAP and Mg in the coated samples. The crystallinity degree of HAP is not changed by Mg addition, while the apatite structure was preserved for all investigated coatings. All investigated samples exhibited typical IR bands of phosphate, carbonate, and hydroxyl functional groups, confirming the formation of apatite phases. By increasing the deposition temperature from room temperature up to 200 °C, the electrochemical behaviour of the coatings, in simulated body fluid and Dulbecco's Modified Eagle Medium, is improved obtaining more electropositive values for corrosion potential, smaller current densities, and higher polarization resistance. The coatings deposited at 200 °C showed the best electrochemical behaviour. Also, by increasing the deposition temperature and incorporating Mg into HAP matrix, the hardness and elastic modulus are increased by more than two-fold, as compared to pure HAP. Furthermore, all coatings deposited on AZ31B alloys are suited for further coating with a mussel-derived surface-binding peptides, but the coatings deposited at 200 °C led to the most regular peptide distribution on the surface. Overall, the results indicated that the biodegradation of HAP + Mg based coatings and the AZ31B alloys can be controlled according to the current clinical needs within implantology field.