Sulfurized PEO-derived coating on biodegradable Zn orchestrates immunoregulation and vascularized osteogenesis for orthopedic applications.

Biodegradable Zn has attracted growing attention as a bone implant material because of its appropriate degradation rate and favourable mechanical properties. In this study, we used plasma electrolytic oxidation (PEO) followed by sulfurization to create a ZnO/ZnS heterostructured coating on Zn (S-PEO-Zn) for orthopedic applications. Surface characterization showed that the coating markedly increased surface roughness and improved wettability. This optimized interface effectively mitigated Zn-induced cytotoxicity and established a favourable local ionic microenvironment. Through controlled Zn ion release, S-PEO-Zn promoted macrophage polarization toward an anti-inflammatory phenotype, associated with downregulation of NF-κB-related inflammatory signalling. Furthermore, S-PEO-Zn enhanced endothelial cell migration and tube formation and upregulated angiogenesis-related gene expression in HUVECs. Meanwhile, S-PEO-Zn enhanced alkaline phosphatase activity and the expression of osteogenesis-related genes in C3H10T1/2 cells. Mouse air-pouch and rat femoral implantation models further demonstrated the favourable immunomodulatory and bone-regenerative effects of S-PEO-Zn in vivo, respectively. Overall, this work demonstrates that ZnO/ZnS-coated Zn represents a promising strategy for orthopedic applications by restoring the immune-vascular-bone coupling cascade.