A sequential functional coating on magnesium alloy: Plasma electrolytic oxidation layer for sustained osteogenic icariin and rapid antibacterial peptide delivery

An icariin/polytrimethylene carbonate (ICA/PTMC) composite coating was constructed on the surface of plasma electrolytic oxidized (PEO) AZ31 alloy, followed by chemical grafting of antimicrobial peptides (AMPs). The PEO coating served as a corrosion-resistant framework, while ICA—a flavonoid compound extracted from the traditional Chinese herb Epimedium —was physically encapsulated with PTMC. ICA can promote bone healing via the Wnt/β-catenin pathway. The outermost layer was functionalized with chemically grafted AMPs to mitigate infection risks following magnesium alloy bone implantation. Results demonstrated that nitrogen (N) element was detected in the coating by EDS and XPS, and FT-IR spectroscopy revealed the characteristic C=O stretching peak of flavonoids, confirming the successful loading of AMPs and ICA. Compared with bare AZ31 ( i ꜀ o ᵣᵣ = 2.57×10 -5 A/cm 2 ) and PEO coating (1.61×10 -6 A/cm 2 ), the PEO-P@I-A coating exhibited a much lower corrosion current of 1.54×10 -9 A/cm 2 and an impedance modulus exceeding 10 7 Ω·cm 2 at 10 -2 Hz. During 21 days of immersion in SBF, the system effectively retarded the degradation rate, with a hydrogen evolution rate of 0.036 mL·cm -2 ·day -1 . In vivo implantation experiments showed stable degradation of the implant within 8 weeks, as evidenced by X-ray and Micro-CT imaging that revealed no gas-induced cavities or osteolysis, with active new bone formation and good osseointegration; no signs of infection were observed. The incorporation of AMPs endowed the coating with superior antibacterial activity during the early implantation stage. This anti-infection function, together with the sustained release of ICA from the underlying layer, synergistically created a favorable microenvironment that supported osteogenic, angiogenic, and anti-inflammatory effects, ultimately promoting bone regeneration. This study provides a novel strategy for the surface modification of degradable magnesium-based bone implants, holding promising application prospects.