Preparation and characterization of polymeric coatings with combined nitric oxide release and immobilized active heparin

A new dual acting polymeric coating is described that combines nitric oxide (NO) release with surface-bound active heparin, with the aim of mimicking the nonthrombogenic properties of the endothelial cell (EC) layer that lines the inner wall of healthy blood vessels. A trilayer membrane configuration is employed to create the proposed blood compatible coating. A given polymeric substrate (e.g., the outer surface of a catheter sleeve, etc.) is first coated with a dense polymer layer, followed by a plasticized poly(vinyl chloride) (PVC) or polyurethane (PU) layer doped with a lipophilic N-diazeniumdiolate as the NO donor species. Finally, an outer aminated polymer layer is applied. Porcine heparin is then covalently linked to the outer layer via formation of amide bonds. The surface-bound heparin is shown to possess anti-coagulant activity in the range of 4.80-6.39 mIU/cm² as determined by a chromogenic anti-Factor Xa assay. Further, the surface NO fluxfrom the underlying polymer layer containing the diazeniumdiolate species can be controlled and maintained at various levels (from 0.5 to 60 x 10^-10 mol cm^-2 min^-1) for at least 24 h and up to 1 week (depending on the fluxlevel desired) by changing the chemical/polymer composition of the NO release layer. The proposed polymeric coatings are capable of functioning by two complementary anti-thrombotic mechanisms, one based on the potent antiplatelet activity of NO, and the other the result of the ability of immobilized heparin to inhibit Factor Xa and thrombin (Factor IIa). Thus, the proposed polymeric coatings are expected to exhibit greatly enhanced thromboresistivity compared to polymers that utilize either immobilized heparin or NO release alone.