Polycaprolactone/hydroxyapatite coating on spark generated Mg surfaces to promote anticorrosion and interfacial adhesion strength

Abstract

Surface coatings have been widely accepted to tailor the degradation rate of Mg alloys for bioimplant applications. Nevertheless, poor adhesion strength resulting in debonding and delamination compromises their corrosion resistance. In the present study, Polycaprolactone/Hydroxyapatite (PCL/HA) coatings have been developed on different textured Mg surfaces obtained under optimized low discharge energy (LDE) and high discharge energy (HDE) conditions of wire electric discharge machining (WEDM). Since discharge energy influences the surface texture of WEDMed Mg alloy, coating on LDE treated surface (LDEedcoated) and coating on the fine-polished surface (Polcoated) showed homogeneous and defect-free coating morphology with contact angles (CA) of 87.85°, 94.05° with simulated body Fluid (SBF) while coating on HDE treated surface (HDEedcoated) displayed spatial defects, lowering the CA. On the LDEedcoated sample, physical anchoring, H2 bonding, and electrostatic interactions combinedly improved the coating's adhesion strength to 9.91 N, 4.5 times higher than the polished counterpart. LDEedcoated samples significantly suppressed the Icorr to 9.74 × 10−9 A/cm2, resulting in 75 % and 99.8 % higher corrosion inhibition efficiency (ηc) after 24 h compared to Polcoated and HDEedcoated samples. After 7 days of in-vitro immersion, the hydrogen evolution rate (HER) of the LDEedcoated sample (0.034 mL/cm2/day) was nearly 2.8 and 35 times lower than Polcoated and HDEedcoated samples, respectively. Superior anticorrosion performance and Ca-P rich apatite growth on LDEedcoated samples significantly improved the cellular viability of L929 cells. WEDM treatments at LDE settings offer a facile method for the preparation of 'substrate-anchored' coating systems with enhanced interfacial adhesion and anticorrosion performance on Mg alloys for clinical translation.