Summary
To reduce the thrombogenic properties of coronary artery stents, a biodegradable polylactic
acid (PLA) stent coating with an incorporated thrombin inhibitor and a platelet aggregation
inhibitor has been developed. In an ex vivo human stasis model, its effect on platelets,
plasmatic coagulation and its release characteristics were studied using whole blood.
Bare steel and bare gold-surface stents were compared to steel and gold-surface stents
coated with PLA (30 kDa) containing 5% polyethyleneglycol (PEG)-hirudin and 1% iloprost,
with an empty tube as control. Markers of activated coagulation (prothrombin fragment
F1-2 and thrombin-antithrombin III complex, TAT), were assayed and the release of drugs
from the coating was assessed by aPTT and collagen-induced platelet aggregation. Bare
steel and gold stents were completely covered by a blood clot, and high levels of
coagulation markers (F1-2 fragment and TAT) were detected. No differences in the thrombogenic properties were
found between bare gold or steel stents. Coated stents were free of blood clots and
only minor elevations of markers were detected. Release data from in-vitro studies
over 90 days showed a gradual release of the drugs with an initial exponential release
characteristic for PEG-hirudin, slow release of iloprost and a 10% degradation of
the PLA carrier. This drug releasing biodegradable coating effectively reduced thrombus
formation independent of the metallic surface.