Bionic Tea Stain-Like, All-Nanoparticle Coating for Biocompatible Corrosion Protection

Magnesium alloys are biodegradable metals, but high corrosion speed and low histocompatibility after implantation still limit the application as biomedical implants. In this work, a bionic coating concept is put forward via mimicking a continuous tea stain formation process, using a layer-by-layer approach. Tannic acid (TA) incorporating Mg2+ ions is used to form a chemical conversion coating on magnesium AZ31 alloy for enhanced corrosion protection and favorable biocompatibility. Thermal oxidation of TA, along with metal-phenol coordination and aggregation, forms an all nanoparticles stacked coating, which is crack-free, homogeneous, more tight, and dense than the pure TA coating. In electrochemical corrosion tests, pH monitoring, and hydrogen evolution tests, the corrosion rate is effectively decreased for the TA/Mg protected AZ31, which is ascribed to the enriched phenol-metal complex and enhanced connections between the individual nanoparticles. With such green chemistry, the introduction of TA and incorporation of Mg2+ synergistically endow the basic requirement of corrosion protection, without cytotoxicity to endothelial cells and with a safe hemolysis ratio. Additionally, this bionic coating effectively suppresses the inflammatory response to AZ31. These results convincingly demonstrate the effectiveness of using such coating as a biocompatible barrier for the potential application of biodegradable magnesium implants.