Graphene and amorphous carbon coatings for nitinol cardiovascular stents by direct chemical vapor deposition: A comparative insight

• Few-layer graphene and amorphous carbon were deposited directly on nitinol cardiovascular stents by ambient-pressure chemical vapor deposition, without interlayers or polymer transfer. • The coatings provided strong corrosion protection, with efficiencies exceeding 80%, while maintaining excellent hemocompatibility. • Amorphous carbon selectively promoted endothelial cell growth while suppressing smooth muscle cell proliferation and inflammatory responses. • This interlayer-free coating strategy offers a simple and multifunctional route for next-generation vascular stent surface engineering. Carbon-based coatings are promising for biomedical implants, including vascular stents, but fabrication on metals often requires adhesion interlayers or polymer-assisted transfer, increasing cost and complexity. Here, we report a simple, ambient-pressure chemical vapor deposition (CVD) process for the direct, interlayer-free growth of two carbon coatings on nitinol (NiTi) stents: few-layer graphene (FLG/NiTi, 170 ± 20 nm) and amorphous carbon (a-C/NiTi, 620 ± 30 nm). Both coatings significantly enhanced corrosion resistance, with protection efficiencies of 83.78% for FLG/NiTi and 89.19% for a-C/NiTi. Vascular cell assays revealed distinct and clinically relevant biological responses. a-C/NiTi promoted vascular endothelial cell (VEC) proliferation (+17.2% at 96 h relative to bare NiTi) while suppressing vascular smooth muscle cell (VSMC) proliferation (−25%), a desirable outcome as excessive VSMC growth drives in-stent restenosis, whereas endothelialization supports vessel healing. In contrast, FLG/NiTi inhibited proliferation of both cell types (>50% reduction for VECs). All samples exhibited excellent hemocompatibility (hemolysis < 0.2%), and a-C/NiTi reduced platelet surface coverage by 30% compared with bare NiTi, beneficial for mitigating thrombosis. Inflammatory assessment further showed a 73% reduction in TNF-α secretion on a-C/NiTi in comparison to bare NiTi. Together, these results demonstrate an interlayer/ polymer-free route to carbon-coated NiTi stents with tunable biological performance.