Photoimmobilisation of poly(N-vinylpyrrolidinone) as a means to improve haemocompatibility of polyurethane biomaterials

A novel method to improve the haemocompatibility of polymeric biomaterials (in particular: polyurethane elastomers) is reported. The new approach essentially rests upon photochemical immobilisation of the highly biocompatible polymer poly(N-vinylpyrrolidinone) (poly(NVP)) onto the biomaterialʹs surface. One of the key steps in the surface modification procedure is the preparation of a copolymer of NVP and the photoreactive building block 4-[4′-azidobenzoyl]-oxo-n-butylmethacrylate (1). This copolymer is first dissolved in a volatile solvent, then sprayed onto the biomaterialʹs surface, and subsequently immobilised via irradiation with ultraviolet light. The paper describes: (i) preparation of 1, (ii) preparation of the copolymer (NVP+1), (iii) physico-chemical characterisation of the modified surfaces, and (iv) results of two in vitro haemocompatibility assays (i.e. thrombin generation and adhesion of blood platelets from recalcified human platelet-rich plasma). Furthermore, the surface modification was performed with a microporous polyurethane vascular graft (Chronoflex®), which is already in clinical use. The in vitro experiments revealed that significant improvement of the haemocompatibility of polyurethanes can be achieved through this method.