Improving magnesium's corrosion resistance through tannic acid–polyethyleneimine coatings for bioresorbable implant applications

Abstract

The high corrosion rate of magnesium limits its application as a bioresorbable implant, despite its good biocompatibility. A tannic acid (TA) coating on magnesium has succeeded in increasing the corrosion resistance of magnesium, although the presence of cracks in this coating still limits its effectiveness. This research focuses on the effect of adding polyethyleneimine (PEI) to the TA coating to increase the corrosion resistance of magnesium and its biocompatibility. The TA–PEI coating on magnesium with TA : PEI weight ratios of 1 : 0, 1 : 0.5, 1 : 1, and 1 : 2, which was achieved by the immersion method, was evaluated by characterizing the composition, morphology, structure, and surface roughness of the coating as well as the deformation mechanism. The corrosion properties and corrosion rate were examined through immersion and electrochemical corrosion tests (potentiodynamic polarization and EIS). Wettability, cell adhesion, and MTT assay tests were carried out as a coating biocompatibility test. The magnesium's surface was successfully covered with the TA–PEI coating, increasing its corrosion resistance and biocompatibility. The increase in the PEI content in the weight ratio of TA : PEI from 1 : 0 to 1 : 2 resulted in a reduction in the areal crack density from 25.49% to 7.12%, an increase in the coating thickness from 5.7 μm to 9.3 μm, a decrease in the surface roughness from 5.20 μm to 0.98 μm, but a change in the deformation mechanism from ductile to brittle. Adding PEI to TA as a pure magnesium coating has increased the material's corrosion resistance. The changed weight ratio of TA : PEI from 1 : 0 to 1 : 2 is the most optimum ratio because it can reduce the corrosion rate of the material from 3.7 mm year⁻¹ to 0.47 mm year⁻¹. The formation of hydroxyapatite on a corroded material indicates that this system is biocompatible. Increasing the PEI content from 1 : 0 to 1 : 2 TA : PEI weight ratio decreased the contact angle from 74° to 24°. At a 1 : 2 TA : PEI ratio, passage 6 HWJ cells can adhere well, and this system has the highest absorbance from the MTT assay result. Both indicate that this coating system has good biocompatibility with human physiochemical systems.