Platelet deposition on stainless steel, spiral, and braided polylactide stents. A comparative study

Platelets play a key role in (sub)acute thrombotic occlusion after stenting. We examined the possible differences between biodegradable polylactide (PLA) and stainless steel (SS) stents in platelet attachment and morphology after whole blood perfusion. PLA stents of different configurations (spiral/braided) and polycaprolactone-polylactide (PCL-PLA)-coatings, or SS stents were implanted into a PVC tube (Ø 3.2 mm), with or without precoating of the tube with type-I collagen. PPACK (30 microM)-anticoagulated blood with (3)H-serotonin prelabeled platelets was perfused (flow rate: 30 ml/min, 90 s) over the stents. Platelet deposition was assessed by scintillation counting and morphology by scanning electron microscopy (SEM). To examine coagulation activation, plasma prothrombin fragments (F1 + 2) were measured before and after the perfusion. Protein deposition on PLA/SS stents was assessed at augmented shear forces mimicking coronary flow (rate: 60 ml/min, 60 s) under minimal anticoagulation (PPACK 1 microM). More platelets deposited on PLA stents than on SS stents under all study conditions (p < 0.03). Under anticoagulation (PPACK 30 microM) the generation of F1 + 2 remained unaltered. Under higher flow rate and limited anticoagulation SS stents accumulated 3.27 +/- 0.75 microg and PLA stents 5.25 +/- 1.74 microg of protein (Mean +/- SD, p <0.95). Among all biodegradable stents, the braided PLA stent coated with PCL-PLA-heparin accumulated the fewest platelets (p < 0.02). In SEM, signs of platelet activation on braided heparin-coated PLA stents, when compared with uncoated braided PLA/SS stents, appeared modest. In conclusion, PCL-PLAheparin coating of biodegradable stents may enhance their hemocompatibility, expressed by less platelet deposition. Nevertheless, materials, design, and coating techniques of biodegradable stents must be further developed.