Stent Coating With Titanium-Nitride-Oxide for Reduction of Neointimal Hyperplasia

Background — Coronary stents prevent constrictive arterial remodeling but stimulate neointimal hyperplasia. Stainless steel induces a metallic foreign body reaction, which is absent for titanium. The hypothesis of the present study was that titanium renders the stent surface biologically inert, with reduced platelet and fibrinogen binding. Methods and Results — Twelve pigs were instrumented with a stainless steel and 2 titanium-nitride-oxide–coated stents (TiNOX 1, ceramic; TiNOX 2, metallic). Animals were restudied after 6 weeks. Histological specimens of stented segments were analyzed by digital morphometry. Platelet adhesion and fibrinogen binding studies were performed in the perfusion chamber. Under in vitro conditions, TiNOX 1 showed reduced platelet adhesion (65±3%) compared with TiNOX 2 (72±5%; P <0.05) and stainless steel (71±4%; P <0.05). Platelet adhesion 48 hours after incubation with human plasma, however, was not different between TiNOX 1 (17±3%) and 2 (15±3%) but was significantly higher with stainless steel (23±2%; P <0.05). Fibrinogen binding was significantly reduced with TiNOX 2 (54±3%) compared with TiNOX 1 (82±4%, P <0.05) or stainless steel (100%, P <0.05). Histomorphometry revealed a significantly larger neointimal area in stainless steel (2.61±1.12 mm 2 ) than in TiNOX 1–coated (1.47±0.84 mm 2 , P <0.02) or TiNOX 2–coated (1.39±0.93 mm 2 , P <0.02) stents. The reductions were 44% and 47%, respectively. Conclusions — TiNOX coating significantly reduces neointimal hyperplasia in stainless steel stents. The antiproliferative effect was similar for both TiNOX coatings, suggesting that the electrochemical properties are more important for attenuation of neointimal proliferation than the observed differences in platelet adhesion and fibrinogen binding.