One-step fabrication of self-healing poly(thioctic acid) coatings on ZE21B Mg alloys for enhancing corrosion resistance, anti-bacterial/oxidation, hemocompatibility and promoting re-endothelialization

Coating magnesium (Mg) alloy stents with biodegradable polymeric materials can address the problems of thrombosis, inflammation, and restenosis caused by poor corrosion resistance and delayed endothelialization; however, these commonly used polymer coatings and their degradation products have no therapeutic effect and sometimes bring extra-side effects. Herein, to develop a polymeric coating with an additional therapeutic effect from that of the polymer itself, a poly(thioctic acid)-based homopolymer was simply synthesized via solvent-free thermal polymerization (containing Zn2+ ions) of thioctic acid (TA), a bioactive ingredient originating from the human body. A Poly(TA-Zn) coating was fabricated on alkali-heat (Mg(OH)2) treated ZE21B alloys via a one-step method, followed by conjugating REDV peptides, to simultaneously enhance the corrosion resistance and re-endothelialization process. Surface characterization and performance were comprehensively investigated. Molecular dynamics (MD) simulations demonstrate that the Zn-O coordination bonds formed between Zn2+ ions and carboxylic groups can inhibit the depolymerization of the Poly(TA-Zn) polymer. SEM micrographs show that the Poly(TA-Zn) coating is homogeneous and has a thickness of 45.03 ± 4.85 μm, and this coating is sturdily bonded to the Mg(OH)2 modified ZE21B substrate. Electrochemical and immersion tests show that the Poly(TA-Zn) sample provides good corrosion protection for ZE21B substrates because of its excellent self-healing properties, and it exhibits superior anti-bacterial/oxidation properties. After immobilizing REDV peptides, Poly(TA-Zn)-REDV samples can substantially hinder platelet adhesion/activation, reduce hemolysis rate, selectively promote the proliferation of endothelial cells and inhibit the growth of smooth muscle cells, thereby improving the anti-coagulation and re-endothelialization ability of Mg substrates.