In tissue engineering, degradable or non-degradable polymer matrices can act as cell-carrier-scaffolds. Cell adhesion and growth on these scaffolds can be promoted by immobilizing extracellular matrix proteins. Therefore, in this study, polymer poly(ethylene terephthalate) (PET) films were surface modified by graft polymerization of acrylic acid, to subsequently allow collagen (types I and III) immobilization and human smooth muscle cell expansion. The surfaces of PET were activated by plasma, followed by acrylic acid graft polymerization, resulting in covalently bound brushes, containing an average of either 0.22+/-0.1 or 5.93+/-0.87 microg/cm2 of poly(acrylic acid) (PAA). Subsequent electrostatic adsorption of collagen gave a surface concentration of 4.96 and 17.2 microg/cm2, respectively, as determined using radiolabelled 125I collagen. Both PET films grafted with 0.22 microg/cm2 of PAA with or without adsorbed collagen were apt for smooth muscle cell adhesion and proliferation. However, films grafted with 5.93 microg/cm2 were not. PAA-grafted PET films, onto which serum proteins of the culture medium adsorbed spontaneously, proved to be better matrices than films on which collagen has been immobilized. It, therefore, can be speculated that other serum proteins are more important than collagen for the human smooth muscle cell adhesion and growth on surface-modified polymer matrices.