Multistep procedure to biofunctionalization of (poly)dimethylsiloxane (PDMS) surfaces is present here, including plasma-based Ar+ beam treatment; acrylic acid grafting; and flexible PEG spacer coupling prior to the Collagen immobilization by peptide synthesis reaction. The success of any step of the Surface modification is controlled by XPS analysis, contact angle measurements, SEM, and AFM observations. To evaluate the effect of PEG chain length, three diNH(2)PEGs (2000, 6000, and 20,000 D) of relative long polymer chain were employed as a spacer, expecting that a long flexible spacer Could provide more conformational freedom for the Collagen molecules and fibroblast reorganization to further cellular matrix formation. Human fibroblast cells were used as a model to evaluate the biological response of the collagen-immobilized PDMS Surfaces. It is found that the earlier described biofunctionalization is one more road to improvement of the cellular interaction of PDMS, the last one being the best when PEG spacer with moderate chain length, namely of 6000 D, is used. (C) 2008 Wiley Periodicals, Inc.