Improvement of poly(ester-urethane) surface properties by RAFT mediated grafting initiated by gamma radiation

• RAFT mediated grafting initiated by γ-rays was performed.
• Narrow molecular weight distributions of grafted chains were achieved.
• Thermosensitive properties of grafted PNIPAAm was confirmed.
• EPR spectra of PUR and grafted PNIPAAm layer were interpreted.

RAFT (ang. Reversible Addition–Fragmentation chain Transfer) polymerization has been considered as one of the most successful techniques for the preparation of polymers with predetermined molecular weights, narrow molecular weight distributions and high degree of chain end functionalities. This method was used for grafting of N-isopropylacrylamide onto polyurethane (PUR) surface to improve biocompability of the matrix surface. The pristine and grafted samples were investigated by the following surface characterization techniques: ATR-FTIR spectroscopy and scanning electron microscopy (SEM). The analysis of paramagnetic species was performed by EPR spectroscopy in order to evaluate the ability of PUR to form covalent bonds with monomer molecules. Grafting of PNIPAAm onto PUR surface in controlled manner was confirmed by GPC. The wettability of PUR and PUR-g-PNIPAAm surfaces was evaluated by contact angle (CA) measurements. Preliminary in vitro cytotoxicity experiments were carried out to study biocompability of pristine and modified samples using MTT assay. Attachment and proliferation of MG-63 osteosarcoma cells on polyurethane films before and after radiation grafting was investigated to assess the potential use of this material for biomedical applications.The applied modification resulted in surface changes of poly(ester-urethane). Polyurethane matrix coated by poly(N-isopropylacrylamide), the polymer classified to the group of thermosensitive polymers, exhibited hydrophilic properties in water at 25 °C, while at 35 °C the surface properties change into hydrophobic. Additionally, narrow molecular weight distribution of the grafted chains was obtained, uniformly covering the surface of the matrix. In vitro studies confirmed that the modified matrices are not cytotoxic when degree of NIPAAm grafting is 14% and number-average molecular weight of the grafted chains (Mn) is about 40,000 g/mol.

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