IMMOBILIZATION OF HEPARIN OLIGOSACCHARIDES ONTO RADIOFREQUENCY PLASMA-MODIFIED PYROLYTIC CARBON-COATED GRAPHITE

Heparin oligosaccharides with different anticoagulant activities were prepared and immobilized onto pyrolytic carbon coated graphite (PC) he art valve materials commonly used in mechanical heart valve prostheses . Prior to immobilization, PC surfaces were modified by radiofrequency plasma polymerized N-vinyl-2-pyrrolidone (PPNVP) thin films (similar to 100 nm) and derivatized to provide surface hydroxyl groups, Cleaved , low affinity heparin (C-heparin) with factor Xa inhibition activity of 107 to 130 IU/mg, was prepared by partial deaminative cleavage of c ommercial crude heparin, and high-affinity heparin (HA-heparin) with f actor Xa inhibition activity of 550 to 1000 IU/mg was prepared by frac tionation of C-heparin using agarose-ATIII affinity chromatography. C- heparin and HA-heparin were immobilized to surface modified PC by redu ctive amination, Anticoagulant activity of the heparin immobilized sur faces was determined by chromogenic assay for the inhibition of factor Xa. Highest surface anticoagulant activity was measured on C-heparin immobilized surfaces (64.0 +/- 7.3 mIU/cm(2)) compared with HA-heparin immobilized surfaces (27.2 +/- 12.2 mIU/cm(2)), suggesting higher bin ding of C-heparin than HA-heparin on the modified PC surfaces. Immobil ized surfaces were evaluated under dynamic flow conditions, by subject ing samples to shear stress of up to 206 dyn/cm(2) in the presence of 5% albumin solution or human plasma. Anticoagulant activity of the imm obilized heparin was retained, although reduced, and the modified surf aces showed evidence for protein resistance. (C) 1995 John Wiley & Son s, Inc.