Tailoring silk fibroin, poly(L-lactic acid) and poly(trimethylene carbonate) coatings on biodegradable magnesium alloy: A comparative evaluation of surface properties, corrosion resistance, and biocompatibility.

Application of biodegradable polymer coatings is a general strategy for addressing rapid corrosion and insufficient biocompatibility of biomedical magnesium (Mg) alloys. In this work, three typical polymer coatings, including silk fibroin (SF), poly(L-lactic acid) (PLLA), and poly(trimethylene carbonate) (PTMC), were fabricated on Mg alloy. Their surface characteristics, degradation behavior, and in vitro biocompatibility were systematically investigated. The polymer coatings all exhibited uniform morphologies, among which PTMC coating had the highest adhesion strength (2.78 N). Electrochemical tests revealed that PTMC coating exhibited optimal corrosion resistance with corrosion current density of 1.51 × 10-7 A/cm2. Its coating-substrate interface remained intact and crack-free after 14 days of immersion in Hank's, demonstrating prominent surface-erosion degradation mode. PTMC coating exhibited the lowest number of adherent platelets, while SF coating showed the highest. Natural antioxidant epigallocatechin gallate (EGCG) was further incorporated into PTMC coating to construct a self-healing layer. The EGCG-loaded PTMC coating exhibited excellent self-healing performance against mechanical scratches in both 0.9 wt% NaCl and Hank's solutions, where the self-healing capacity positively correlated with EGCG content (2 mg/mL > 1 mg/mL). The self-healing capability stems from the synergistic sealing by both in situ formed Mg2+-EGCG chelates and insoluble inorganic corrosion products. This study clarifies the differences in comprehensive properties of polymer coatings on Mg alloys and provides a feasible strategy to develop self-healing biodegradable coatings for Mg-based implant.