Evaluation of corrosion resistance, mechanical integrity loss and biocompatibility of PCL/HA/TiO2 hybrid coated biodegradable ZM21 Mg alloy

A novel PCL/HA/TiO2 hybrid coating on ZM21 Mg alloy substrate has been investigated for corrosion resistance, biocompatibility and mechanical integrity loss in terms of bending, compressive and tensile strength in physiological media. The prepared hybrid coating was dip coated over ZM21 from HA/TiO2 and PCL solutions followed by creating a microporous PCL layer by utilizing Non-solvent Induced Phase Separation (NIPS) technique. The electrochemical measurement and in-vitro degradation study in SBF after 28 days showed that the PCL/HA/TiO2 hybrid coating reduced H2 evolution rate, weight loss, and corrosion rate by 64, 116 and 118 times respectively, as compared to uncoated ZM21 samples. The surface studies carried out using SEM-EDX, FTIR and XRD revealed formation of highly stable 3d flower-like HA crystals with Ca/P ratio of 1.60 in the PCL micropores. This dense apatite growth effectively protected the PCL/HA/TiO2 hybrid coated samples to maintain the good mechanical integrity even after 28 days of immersion as compared to HA/TiO2 composite coated, As-polished (A/P) and As-machined (A/M) samples. The failure analysis of samples under mechanical loading were performed using SEM-BSE-EBSD. The in-vitro cellular viability of L929 fibroblast cells on PCL/HA/TiO2 hybrid coating was found 50.47% higher with respect to control group, whereas bacterial viability was supressed by 57.15 and 62.35% against gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacterial models. The comprehensive assessment indicates PCL/HA/TiO2 hybrid coating as a suitable candidate to delay early degradation and mechanical integrity loss of Mg-based alloys for devising biodegradable orthopaedic implant.