Sustainable Walnut Shell-Filled Polylactic Acid–Hydroxyapatite Hybrid Coatings for Enhanced Corrosion Resistance and Bioactivity of Magnesium Biomaterials

Due to the high corrosion rate and limited biocompatibility of commonly used magnesium (Mg) and its alloys, current studies have focused on surface modification techniques. In this study, which is aimed at overcoming these obstacles in biomedical applications, hybrid coatings of PLA-HA-Walnut shell (Wshell) were successfully applied to Mg substrates. The presence of micropores on the surfaces of the hybrid coatings was detected using SEM surface morphology, and the elemental composition and structural characterization of the coatings were confirmed through analyses. With a higher Wshell fraction, the corrosion current density decreased significantly compared to uncoated Mg and PLA-coated Mg, increasing the electrochemical corrosion resistance of Mg. The adhesion strength between the coatings and the Mg substrates increased to grade 3B with Wshell-filled hybrid coatings. Moreover, the contact angle of PLA-coated Mg decreased as the Wshell fraction increased, indicating enhanced surface wettability. Wshell hybrid coatings exhibit fibrous morphology and the formation of Ca- and P-rich layers. These results, along with the filling of Wshell, suggest that PLA-HA-Wshell hybrid coatings could be a promising additive material for potential next-generation low-cost and sustainable biomedical coatings to enhance the corrosion resistance and bioactivity of Mg.