Mg-Incorporated Egcg Coating on AZ31 with Biocompatible Corrosion Protection for Vascular Implants

Abstract

As a promising biodegradable metallic material, magnesium (Mg) and its alloys have attracted special attention in recent decade. However, challenges still remain due to its high corrosion rate and insufficient biocompatibility after implantation. In this work, we put forward a coating concept on AZ31 surface via mimicking a 'tea stain' formation process using a layer-by-layer approach. Epigallocatechin gallate (EGCG) incorporating Mg2+ ions is used to form a chemical conversion coating on AZ31 magnesium alloy with enhanced corrosion protection and favorable biocompatibility for cardiovascular implants. The SEM and AFM morphology results revealed that with the incorporation of Mg2+, the as-formed EGCG/Mg coating was more homogeneous and dense, with far more less cracks than the pure EGCG coating. The in vitro degradation rate and corrosion resistance were studied by electrochemical corrosion tests and monitoring of the changed pH value and hydrogen evolution, respectively, which revealed that the corrosion rate of EGCG/Mg riched coating was effectively decreased than that of pure EGCG coating and bare AZ31 substrate. Owing to the mild degradation rate, in combination of the biological function of EGCG, enhanced endothelial cells (ECs) adhesion and proliferation, suppressed smooth muscle cells (SMCs) adhesion/proliferation and inhibited cytokine release were observed on EGCG/Mg coated AZ31 alloy. Besides, the in vivo subcutaneous embedding experiment strongly indicated that the EGCG/Mg coating performed more mild tissue response due to the improved corrosion resistance to surrounding microenvironment. Ex-vivo thrombogenicity test demonstrated the EGCG/Mg coatings presented an impressive improvement in anti-thrombogenicity compared to bare AZ31. These results convincingly demonstrated the potential of using Mg-incorporated EGCG coating as a biocompatible barrier on the biodegradable magnesium alloy for vascular implants.