Synthesis of photoreactive poly(ethylene glycol) and its application to the prevention of surface‐induced platelet activation

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Abstract
Photoreactive poly(ethy1ene glycol) (PEG) was synthesized by reacting 4‐fluoro‐ 3‐nitrophenyl azide (FNPA) with sodium salt of PEG. The synthesized 4‐azido‐2‐ nitrophenyl PEG (ANP‐PEG) was charac‐ terized by 1H‐NMR, IR, and UV spectro‐ scopy. ANP‐PEG was grafted to dimethyldichlorosilane‐coated glass (DDS‐glass) by photolysis without any premodification of the surface. The effects of various grafting factors, such as the polymer adsorption time, concentration of ANP‐PEG, and UV irradiation time, on the PEG grafting efficiency were examined. The PEG‐grafted DDS‐glass was characterized by measuring surface free energies, surface‐induced platelet activation, and the relative amount of PEG grafted on the surface using electron spectroscopy for chemical analysis (ESCA). Platelet adhesion and activation was analyzed by measuring the number and spread area of adherent platelets. The results showed that ANP‐PEG had to be adsorbed onto DDS‐glass for at least 12 h before photolysis for the maximum grafting efficiency. No platelets could adhere to the PEG‐grafted DDS‐glass, if the bulk concentration of ANP‐PEG in the adsorption solution was between 1 mg/mL and 10 mg/mL. Above 10 mg/mL, platelet activation gradually increased and reached the maximum at 30 mg/mL. Our data indicate that the grafting of ANP‐PEG requires careful control of the grafting conditions and that the grafted PEG can prevent surface‐induced platelet activation.