The aim of this research was to determine the influence of argon plasma treatment condition on the surface properties of poly(ethylene glycol) diacrylate (PEGDA)hydroxyethly methacrylate hydrogel films, a kind of scaffold materials for tissue engineering. The changes of surface properties have been evaluated by contact angles, X-ray photoelectron spectra (XPS), and scanning electron microscopy (SEM). From the contact angle measurements of different liquids, the surface free energy of the hydrogel was calculated according to approaches by OwensWendtKaelble. Results showed that the contact angle of the hydrogel to water decreased remarkably after argon plasma treatment, which was caused by the changes in morphology (SEM images) and chemical composition (XPS results) of the argon plasma-treated surface. The surface free energy increased with the increase of the argon plasma treated time and power, and these increasing was mainly due to the increase of polar component. The XPS results confirmed that plasma oxidation reaction produced oxygen-containing functional groups onto the surface. This functional group played an important role in increasing the hydrophilic properties of the hydrogel. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012