Biphasic zinc phosphate coating improves vascular remodeling and systemic biocompatibility of zinc: A wire-based model for biodegradable venous stent applications.

Permanent venous stents can cause late biological and mechanical complications, motivating the development of biodegradable alternatives. Zinc has a favorable degradation profile for vascular implants, but uncontrolled zinc ion release may impair endothelial repair, particularly under low-flow venous conditions. In this study, a biphasic zinc phosphate (ZnP) conversion coating was formed on pure zinc by microwave-assisted processing and evaluated in vitro and in a rat inferior vena cava wire implantation model as a proof of concept. The coating comprised granular zinc phosphate domains and sodium zinc phosphate crystals, exhibited strong interfacial integrity, and supported endothelial cell attachment and migration while reducing smooth muscle cell metabolic activity and migration. In vivo, uncoated zinc was associated with delayed tissue maturation, persistent local inflammation, and transient hepatic and hematological responses. The ZnP coating remained largely intact at two weeks and underwent gradual microscale degradation by four weeks. Quantitative degradation analysis revealed that the ZnP coating significantly mitigated early anodic dissolution of the zinc substrate by approximately 33% at two weeks and maintained a stable in vivo corrosion rate of 0.13 mm/y at four weeks. Coated implants showed a significantly higher CD31-positive endothelial coverage exceeding 80% compared to the uncoated group, accompanied by more organized collagen deposition, normal hematological parameters, no histopathological abnormalities in major organs, and no sustained increase in serum zinc levels. These findings indicate that the biphasic ZnP coating can mitigate zinc degradation and improve local and systemic biocompatibility in a venous environment, demonstrating the preliminary efficacy of this wire-based proof-of-concept model for supporting the future design of biodegradable zinc-based venous stents.