Thrombogenicity markers in clinical and ex vivo assessment of membrane biocompatibility

Surface modification of the polymers present in a polysulfone hollow fiber hemodialyser 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 modification of various polymers, i.e. polysulfone (PSU), polycarbonate (PC), and polyurethane (PU), which constitute the Ultraflux AV 600 S hollow fibre hemodialyser. An investigation was first made into six different chemical routes aimed at introducing carboxyl groups onto the surface of PSU, PC, and PU model polymers to which heparin (HE) or endothelial cell surface heparan sulfate (ESHS) was covalently bound via the reaction of residual amino groups and a coupling reagent. Carboxyl groups were introduced using three specific reactions based on their nucleophilic or electrophilic introduction into aromatic repeating units of the polymers and three non-specific carboxylation reactions, i.e. UV, heat or redoxactivation via nitrene or radical species. Concentrations of 1-20 nmol COOH groups per cm(-2) led to HE or ESHS surface concentrations corresponding to one or several layers. Two nonspecific carboxylation reactions followed by HE- or ESHS-coupling provided the lowest change in membrane pore structure according to cut off, clearance (urea, phosphate, maltose), ultrafiltration, and diafiltration assessments. In some cases the introduction of excess negatively-charged carboxyl groups and HE improved the flux properties of the modified membranes. The various methods were applied to the dialysis module. Platelet adhesion was not observed 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, respectively, under similar conditions. The coating of PSU or of other high-flux membranes by ESHS appears a promising method for improving membrane properties and to generate biocompatibility characteristics similar to those of natural blood vessels, i.e. inertness to platelet adhesion and no level effects for complement and intrinsic coagulation cascade activation. The ESHS coating may be used without anticoagulants.