Corrosion-resistant and bioactive FeMn-CaP-Col@CS coating on magnesium alloy for orthopedic implants: Fabrication and characterization

To address the rapid degradation behavior of magnesium alloys in physiological environments, a multifunctional gradient FeMn-CaP-Col@CS composite coating was fabricated on the surface of biodegradable WE43 magnesium alloy. The FeMn alloy interlayer was deposited via filtered cathodic vacuum arc (FCVA) technology, with optimized substrate bias voltage and deposition parameters to improve corrosion resistance and mechanical performance. Subsequently, a calcium phosphate (CaP) layer and a bioactive polymer layer composed of collagen (Col) and chitosan (CS) were sequentially introduced via chemical conversion treatment to construct a compact, uniform multilayer coating. The sample with FeMn-CaP-Col@CS composite coating exhibited a significantly reduced corrosion current density compared to uncoated WE43, along with a markedly increased impedance. Biological evaluations, including cytocompatibility assays and live/dead cell staining, indicated excellent cell viability and adhesion on the coated samples. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis revealed upregulated expression of osteogenesis-related genes. The composite coating effectively maintained a favorable microenvironment while providing moderate osteoinductivity due to the synergistic effect of Col and CS. In summary, the FeMn-CaP-Col@CS gradient coating system substantially enhances the corrosion resistance and biocompatibility of WE43 magnesium alloy, offering a promising strategy for the clinical application of magnesium-based orthopedic implants. In this study, a non-magnetic FeMn coating was successfully deposited on the surface of WE43 magnesium alloy using filtered cathodic vacuum arc (FCVA) technology by optimizing the deposition parameters. To further enhance the corrosion resistance, biocompatibility, and osteogenic potential of the coating, a Col@CS layer was applied onto the FeMn coating via chemical conversion. Given the hydrophilicity and strong adhesion of calcium phosphate (CaP), a CaP transition layer was introduced between the FeMn and Col@CS layers to improve interfacial bonding. As a result, a multifunctional FeMn-CaP-Col@CS gradient coating was successfully developed. The gradient coating enhances the corrosion resistance, biocompatibility and osteogenic differentiation ability of the substrate. • A multifunctional FeMn-CaP-Col@CS gradient coating has been successfully developed. • FeMn-CaP-Col@CS gradient coating exhibited excellent anti-corrosion properties. • FeMn-CaP-Col@CS coating has good cytocompatibility and osteogenic ability.