Influence of surface texture and charge on the biocompatibility of endovascular stents

The mechanical behaviour and the surface characteristics of endovascular stents are key factors determining stent patency. In-vitro studies have suggested that surface texture and charge alter the biocompatibility of metallic stents. In this study, the influence of surface texture and charge of metallic stents on thrombosis and neointima formation was evaluated in a rabbit model.

Twenty-four stainless steel Palmaz-Schatz stents were coated either by an electrochemical deposition of metal on the stent surface or were coated with a metallic film which was implanted into the stent surface by argon ion bombardment. The coatings consisted of platinum, gold, or copper. Coated and uncoated control stents were implanted in rabbit iliac arteries. As antithrombotic therapy, 500 IU heparin and 60 mg aspirin was given intravenously before stent implantation, followed by 60 mg aspirin intravenously every third day for 4 weeks. Thrombus and neointima formation in arterial cross-sections of 24 coated stents were compared with 19 uncoated stents using quantitative, computer-assisted histomorphometry and transmission electron microscopy.

A higher stent surface porosity and more surface cracks after stent expansion were found after galvanization than after ion implantation. The in-vitro surface potentials of uncoated steel, copper-, and gold-coated or platinized stents were +150, +120, +180, and +180 mV, respectively. Four weeks after implantation, six of 14 galvanized stents, but none of the uncoated or ion bombarded stents, were occluded by a thrombus. Neointimal hyperplasia was increased in stents coated by galvanization compared with stents coated by ion implantation. In both study groups, the most electropositive coating (platinum or gold) induced markedly less neointima formation than the least electropositive (copper).

Stent surface texture was the most important factor determining biocompatibility of coated Palmaz-Schatz stents in this study. In contrast to suggestions derived from in-vitro studies, the charge of stents does not seem to play a major role with respect to stent thrombogenicity. Low stent charge correlates with an increased neointima formation.