Eco-Friendly In-Situ Zwitterionization of Stent Metals with Phosphonic Sulfobetaine Copolymers for Durable Antibiofouling and Hemocompatibility

Abstract

Although stainless steel (SS) is widely used for cardiovascular stents, its surface is prone to undesirable biological interactions that contribute to thrombosis, infection and restenosis. In this study, zwitterionic copolymers composed of poly(vinylphosphonic acid) (PVPA) and poly(4-vinylpyridine propylsulfobetaine) (P4VPPS) were successfully synthesized, structurally characterized, and grafted onto SS surfaces via a green, water-based approach. Dynamic vapor sorption and zeta potential measurements revealed hydration characteristics governed by the balance between phosphonic acid and zwitterionic segments. Among the copolymers, VPA/4VPPS ratio of 70/30 (VPS70) exhibited the most favorable hydration behavior, and near neutral surface charge, which collectively resulted in superior antifouling and bioinert performance. The VPS70-grafted SS surface effectively suppressed adhesion of fibroblast cells (reduced by 83.7%), Escherichia coli (reduced by 68.8%), and blood components (reduced by 78.8%), while maintaining good cytocompatibility (88.3% cell viability), nonhemolytic behavior (0% hemolysis), and without affecting blood coagulation (PT and APTT values comparable to the control). Notably, VPS70 retained its bioinert properties after steam sterilization at 121 °C, demonstrating superior thermal stability over sulfobetaine methacrylate-based systems. These results establish VPS70 as a promising grafting material for cardiovascular SS-based stents capable of minimizing blood cell and bacterial adhesion, reducing dependence on antithrombotic therapy, and mitigating restenosis. Moreover, this water-based grafting method offers a simple and practical way to modify SS surfaces used in blood-contacting medical devices.