In fl uence of stent surface microstructuring on endothelial cell migration and substrate thrombogenicity

Background: Coronary stent implantation is currently one of the most performed cardiovascular interventions, but requires a long-term therapy with anti-platelet agents to prevent stent thrombosis. Stents with microstructured surfaces should improve stent vascularisation, reduce thrombotic events and consequentially shorten the length of anti-thrombotic therapy. Methods: Differently designed, 2-5 mm high elevations or hollows were lithographically etched on silicon plates, subsequently coated with silicon carbide. As controls, smooth silicon plates, bare metal substrates, and cell culture plastic were used. The migration of human umbilical vein endothelial cell (HUVECs) was assessed in a modified barrier assay using cell culture inserts (n1⁄410). 8h/24h after cell seeding, inserts were removed and cell migration was monitored for 2, 20, 30, 40, 60, and 72 hours. Actin cytoskeleton was visualised with green phalloidin. Platelet concentrate or whole blood were incubated on the different surfaces in static and flow conditions to investigate surface thrombogenicity (n1⁄410). For cell counting, P-selectin antibody conjugated with fluorescein was used. Images were taken with an incident light fluorescent microscope used for studies of non-transparent objects. Results: Comparing different types of structured surfaces, improved endothelial cell migration over 72h was observed for 4-5 mm pillow-like structures, whereas smaller spiky structures (2 mm), hollows, and smooth surfaces (i.e. smooth silicon plates, bare metal substrates) had a negative effect on endothelial migration. Moreover, substrate specific interactions between the tested endothelial cells and the structure relief could be detected. The thrombogenicity assays under static and flow conditions performed using whole blood and platelet concentrate showed that the platelet adhesion was reduced on larger structures as compared to smaller sharp-edged structures, hollows, or the smooth surfaces. Conclusions: Microstructured surfaces have strong influence on endothelial cell migration and platelet adhesion. These results open new possibilities to design stent surfaces which improve adherence and migration of endothelial cells, and inhibit thrombogenic processes.