Efficient and smart hybrid coatings for active corrosion protection of magnesium alloys

This article discusses potential solutions to overcome current limitations for clinical implementation of Mg implants by forming the biocompatible hybrid PEO-based inhibitor- and polymer-containing coatings for a controlled corrosion degradation of the bioresorbable material. Multifunctional hybrid coatings were obtained on MA8 magnesium alloy. The porous ceramic-like coating synthesized by plasma electrolytic oxidation served as a base for further modification with bioresorbable polymer (polycaprolactone, PCL) contained halloysite nanotubes (HNTs) with corrosion inhibitor (benzotriazole, BTA). The method for HNT impregnating with BTA and introducing them into the matrix of PCL was proposed. The chemical composition of the protective layers was studied using SEM-EDX, XRD, XPS, and Raman microspectroscopy. Anticorrosion protection level of the coated specimens was determined by means of electrochemical techniques, weight loss, and hydrogen evolution tests. The samples with hybrid layers showed the best corrosion protection during 23 h exposure to Hanks’ Balanced Salt Solution (|Z|_{f = 0.1 Hz} = 1.02 MΩ·cm², I_C = 11 nA·cm^–2, R_p = 2.4 MΩ·cm²) and the lowest degradation rate (0.021 mm/year) after 7 day of exposure to HBSS among all the tested samples. The electrochemical activity on microscale of samples with the studied coatings was estimated by localized electrochemical techniques. The degradation mechanism of specimens with hybrid layers was proposed. The prospects of hybrid layer application in regulating the resorption process of Mg alloys were shown.