Complement activation on degraded polyethylene glycol-covered surface

Surface modification with polyethylene glycol (PEG) has been employed in the development of biomaterials to reduce unfavorable reactions. However, unanticipated body reactions have been reported, with activation of the complement system being suggested as having involvement in these responses. In this study, we prepared a PEG-modified surface on a gold surface using a monolayer of α-mercaptoethyl-ω-methoxy-polyoxyethylene. We observed neither protein adsorption nor activation of the complement system on the PEG-modified surface just after preparation. Storage of the PEG-modified surface in a desiccator under ambient light for several days or following ultraviolet irradiation, reflection–adsorption (FTIR-RAS) and X-ray photo spectrometry revealed deterioration of the PEG layer, which became a strong activator of the complement system through the alternative pathway.