Microwave-assisted immobilization of heparin onto polyurethane surface for improving blood compatibility

Heparin was covalently immobilized onto polyurethane surface via a PEG spacer by a microwave-assisted approach to improve blood compatibility. Firstly, amino-terminated poly(ethylene glycol) (APEG) was rapidly grafted onto PU surface within 20 min by a two-step method involving microwave-assisted MDI-functionalization and subsequent microwave-assisted APEG coupling. Then, heparin was covalently immobilized through an amide linkage by the direct coupling of the carboxylic acid of heparin with the amino group of APEG on PU surface using carbodiimide coupling reaction. The surface structure and properties were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurements. The results revealed that heparin-immobilized PU surface had slightly increased roughness and significantly improved hydrophilicity in comparison to the original PU surface. The anticoagulant activity of films was evaluated by whole blood clotting time (CT) and prothrombin time (PT). Complement activation was assessed by detecting complement fragment 3a concentrations of serum exposed to the films. The results revealed that the microwave-assisted heparin-immobilized PU films had excellent antithrombogenicity and suppressed complement activation, indicating improved blood compatibility.