Surface modification of the polymers present in a polysulfone hollow fiberhemodialyser by covalent binding of heparin or endothelial cell surface heparan sulfate: Flow characteristics and platelet adhesion

The present study addresses the problem of simultaneous surface modificatio n of various polymers, i.e. polysulfone (PSU), polycarbonate (PC), and poly urethane (PU), which constitute the Ultraflux AV 600 S(R) hollow fibre hemo dialyser. An investigation was first made into six different chemical route s aimed at introducing carboxyl groups onto the surface of PSU, PC, and PU model polymers to which heparin (HE) or endothelial cell surface heparan su lfate (ESHS) was covalently bound via the reaction of residual amino groups and a coupling reagent. Carboxyl groups were introduced using three specif ic reactions based on their nucleophilic or electrophilic introduction into aromatic repeating units of the polymers and three non-specific carboxylat ion reactions, i.e. UV, heat or redoxactivation via nitrene or radical spec ies. Concentrations of 1-20 nmol COOH groups per cm(-2) led to HE or ESHS s urface concentrations corresponding to one or several layers. Two nonspecif ic carboxylation reactions followed by HE- or ESHS-coupling provided the lo west change in membrane pore structure according to cut oft; clearance (ure a, phosphate, maltose), ultrafiltration, and diafiltration assessments. In some cases the introduction of excess negatively-charged carboxyl groups an d HE improved the flux properties of the modified membranes. The various me thods were applied to the dialysis module. Platelet adhesion was not observ ed in the case of the ESHS-coating of PSU membrane at shear rates of 1050 s (-1), whereas HE and subendothelial matrix showed 56 and 100% coverage, res pectively, under similar conditions. The coating of PSU or of other high-fl ux membranes by ESHS appears a promising method for improving membrane prop erties and to generate biocompatibility characteristics similar to those of natural blood vessels, i.e. inertness to platelet adhesion and no level ef fects for complement and intrinsic coagulation cascade activation. The ESHS coating may be used without anticoagulants.