INFLUENCE OF SURFACE TEXTURE AND CHARGE ON THE BIOCOMPATIBILITY OF ENDOVASCULAR STENTS

Background: The mechanical behaviour and the surface characteristics o f endovascular stents are key factors determining stent patency. In-vi tro studies have suggested that surface texture and charge alter the b iocompatibility of metallic stents. In this study, the influence of su rface texture and charge of metallic stents on thrombosis and neointim a formation was evaluated in a rabbit model. Methods: Twenty-four stai nless steel Palmaz-Schatz stents were coated either by an electrochemi cal deposition of metal on the stent surface or were coated with a met allic film which was implanted into the stent surface by argon ion bom bardment. The coatings consisted of platinum, gold, or copper. Coated and uncoated control stents were implanted in rabbit iliac arteries. A s antithrombotic therapy, 500 IU heparin and 60 mg aspirin was given i ntravenously before stent implantation, followed by 60 mg aspirin intr avenously every third day for 4 weeks. Thrombus and neointima formatio n in arterial cross-sections of 24 coated stents were compared with 19 uncoated stents using quantitative, computer-assisted histomorphometr y and transmission electron microscopy. Results: A higher stent surfac e porosity and more surface cracks after stent expansion were found af ter galvanization than after ion implantation. The in-vitro surface po tentials of uncoated steel, copper-, and gold-coated or platinized ste nts were +150, +120, +180, and +180 mV, respectively. Four weeks after implantation, six of 14 galvanized stents, but none of the uncoated o r ion bombarded stents, were occluded by a thrombus. Neointimal hyperp lasia was increased in stents coated by galvanization compared with st ents coated by ion implantation. In both study groups, the most electr opositive coating (platinum or gold) induced markedly less neointima f ormation than the least electropositive (copper). Conclusion: Stent su rface texture was the most important factor determining biocompatibili ty of coated Palmaz-Schatz stents in this study. In contrast to sugges tions derived from in-vitro studies, the charge of stents does not see m to play a major role with respect to stent thrombogenicity. Low sten t charge correlates with an increased neointima formation.