Thrombus formation at the surface of guide-wire models: effects of heparin-releasing or heparin-exposing surface coatings.

PURPOSE: This study was conducted to investigate whether thrombus formation at the surface of guide wires occurs, and--if so--whether this can be suppressed or prevented through incorporation of heparin in the surface coating. MATERIALS AND METHODS: Five guide wire models were examined; three had a polymeric hydrophilic surface coating (90/10 guide wire), which was either heparin-free, impregnated with sodium-heparin (Na-hep), or impregnated with benzalkonium heparin (BAK-hep). The other two guide wires had a coating of polytetrafluoroethylene (PTFE), either without heparin, or impregnated with BAK-hep. Release of heparin, exposure of heparin at the surface of the guide wires, thrombogenicity (under static and flow conditions) and their propensity to attract blood platelets were investigated. RESULTS: The guide wire 90/10 Na-hep releases approximately 150-200 mU active heparin per cm coil within the first few minutes after incubation in buffer. The PTFE BAK-hep shows a relatively slow release of 60-70 mU active heparin per cm coil. The 90/10 BAK-hep showed no released heparin but the most exposed heparin. In a static experiment with human full blood excessive thrombus formation occurred at the heparin-free models, whereas the others remained essentially clean. In a thrombin-generation assay under flow the authors observed strong retardation of thrombin formation in the case of the 90/10 Na-hep guide wire. CONCLUSIONS: The static and dynamic in vitro assays, taken together, show that the 90/10 Na-hep provides a coating with an extremely low level of surface thrombogenicity. Use of a guide wire with a hydrophilic distal coating that releases and exposes sodium heparin may contribute to the safety of diagnostic and therapeutic interventional procedures.

Coils and tubes releasing heparin. Studies on a new vascular graft prototype.

Coiled metallic guidewires find widespread use, for instance in interventional cardiology. It is known that release of heparin from the surface of guidewires is advantageous to prevent formation of thrombotic emboli. New coiled tubular structures, having larger inner and outer diameter as compared to guidewires, are presented. In theory these tubes can be used as interposition vascular grafts. Ten coiled tubes with an internal diameter of 690 microm were made. Five different adherent polymeric coatings with increasing hydrophilicity were used. Five tubes contained heparin in the coating and the other five were unheparinised controls. The five tubes containing heparin were studied with respect to heparin release in vitro (amount released, kinetics), and immobilised heparin that is exposed at the surface. All tubes were studied with a direct cell contact assay using 3T3 mouse fibroblast cells, a dynamic thrombin generation test, and endothelial cell growth onto the coils. It was found that the heparinised tubes lead to very little thrombin formation. It is argued that this is due to heparin that is immobilised and exposed at the inner surface of such tubes. Furthermore the coils showed to be cytocompatible and endothelial cells adhere and proliferate well onto the coils. This concept is believed to hold promise for further development of small vascular grafts.