Synthesis of photoreactive pullulan for surface modification

Photoreactive pullulan was prepared, the polymer was photoimmobilized on polymeric or organic surfaces, and its interactions with a protein and a cell type were investigated. The photoreactive pullulan was synthesized by a coupling reaction with 4-azidobenzonic acid. Surface modification was carried out in the presence or absence of a micropatterned photomask containing 100 μm transparent stripes with 150 μm gaps, making it easy to confirm the immobilization. By the micropatterning method, immobilization of the photoreactive pullulan on polystyrene, polyethylene, and silane-coupled glass was confirmed. Contact angles were measured on the unpatterned surfaces. Although the original surfaces have different contact angles, the contact angle on Az-pullulan-immobilized surface was the same on all surfaces. This result demonstrated that photoimmobilization completely covered the surface with Az-pullulan. Protein adsorption was investigated using fluorescently labeled albumin applied to the micropatterned surface: fluorescence microscopy demonstrated that adsorption was reduced on the pullulan-immobilized regions. Culture of RAW264 cells, derived from mouse leukemic monocytes, on the micropatterned surface for 22 h showed that cells did not adhere to the immobilized pullulan regions. In conclusion, photoreactive pullulan was covalently immobilized on various surfaces and tended to reduce interactions with proteins and cells.