Chemical–Physical Characterization of Polyurethane Catheters Modified with a Novel Antithrombin-Heparin Covalent Complex

Detailed structural studies were made of polyurethane catheter surfaces modified with a covalent antithrombin-heparin (ATH) complex that has superior anticoagulant activity compared to unfractionated heparin. ATH was grafted onto polyurethane catheters by surface film preparation involving a three-step process: (1) activation of ATH through functionalized poly(ethylene glycol) (PEG), (2) base-coating treatment of the polyurethane surface and (3) final attachment of ATH onto the surface by free radical polymerization. With the application of base coating, composed of polyhydroxyethylmethacrylates and poly(ethylene oxide) (PEO), the coating process could easily be transferred to other biomaterials by adjusting the base-coating composition. Anti-factor Xa assays confirmed high anticoagulant activity of the ATH coatings. To determine structural aspects critical for biological function, the product was analyzed using differential scanning calorimetry and SDS-PAGE. Radiolabeled ATH was used to determine the graft density, homogeneity and stability of modified surfaces, as well as the competition of PEO-ATH migration to the surface with self-aggregation of the PEO-ATH molecules during the coating process. X-ray photoelectron spectroscopy was used to investigate the surface chemical composition before and after ATH application. Analysis showed that PEO-ATH was strongly surface-bound at a final density of 15-200 pmol/cm(2), depending on the incubation concentration.