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Photoreactive poly(ethylene 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 characterized by 1H-NMR, IR, and UV spectroscopy. 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.

Albumin and fibrinogen were competitively adsorbed onto dimethyldichlorosilane-coated glass (DDS-glass) and platelet activation was examined as a function of the surface fibrinogen concentration. The weight ratio of albumin to fibrinogen in the adsorption solution was varied from 10 to 700. Platelet activation was quantitated by the area and circularity of spread platelets. When the DDS-glass was coated with albumin alone, platelets were only contact adherent and could not spread at all. After competitive adsorption of fibrinogen and albumin, however, platelets were able to spread on the surface. Platelet activation increased linearly as the surface fibrinogen concentration increased up to 0.02 micrograms/cm2. Platelets were able to activate fully if the surface fibrinogen concentration was 0.02 micrograms/cm2 or higher, even though the surface was dominated by albumin. It appears that platelets can activate fully as long as only a small fraction (2-15%) of the surface is covered with tightly bound fibrinogen.

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