Hydroxyapatite-containing PEO-coating design for biodegradable Mg-0.8Ca alloy: Formation and corrosion behaviour
Andrey S. Gnedenkov, Sergey L. Sinebryukhov, V. S. Filonina, С. В. Гнеденков
Abstract
In this study, the biocompatible protective coating was formed using plasma electrolytic oxidation (PEO) on bioresorbable Mg-0.8Ca alloy. The composition of the formed coating was studied using XRD, SEM-EDX analysis, and micro-Raman spectroscopy. The uniform distribution of hydroxyapatite over the thickness of protective PEO-layer was established. Using traditional (EIS, PDP, OCP) and local scanning electrochemical methods (SVET, SIET with H+-selective microelectrode), the level of protective properties of PEO-layer in a biological environment (mammalian cell culture medium, MEM) was determined. It was established that modification of Mg-0.8Ca alloy surface by PEO contributes to a significant increase in the corrosion resistance of the surface layer, making it possible to control the process of material`s biodegradation. The maximum local electrochemical activity was recorded after 72 h of testing, while for the uncoated sample, intense corrosion degradation was recorded in the first 12 min of exposure to the cell culture medium. Formation of the PEO-coating results in a twofold decrease in the corrosion current density (2.8ˑ10−6 A cm−2) and an increase in the impedance modulus measured at a low frequency (1.7ˑ104 Ω cm2) in comparison with the uncoated material (9.5ˑ10−6 A cm−2; 8.1ˑ103 Ω cm2). The mechanism of material bioresorption was established and a model for biodegradation process of Mg-0.8Ca alloy with hydroxyapatite-containing PEO-coating in MEM was proposed. Analysis of these results and comparing with others obtained by various scientific groups indicate the prospects for application of biocompatible PEO-coating on Mg-Ca alloy in implant surgery.