In this manuscript, Ar plasma treated polyethyeterephthalate grafted with biphenyl-4,4'-dithiol interlayer and subsequently with green synthesized Pt and Pd nanoparticles is studied, focusing on the cytocompatibility of those composites. Changes in surface properties of the plasma treated and nanoparticle-grafted PET surface were studied in relation to in vitro adhesion and proliferation of mouse fibroblasts (1929) and human osteoblast (U-2 OS). Prepared samples were studied by several experimental techniques: goniometry, angle resolved X-ray photoelectron spectroscopy (ARXPS), ultraviolet visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS) and electrokinetic analysis. Ageing of the modified PET was accompanied by an increase of the contact angle which was due to a reorientation of the molecular polar segments produced during the plasma treatment. FTIR, UV-vis, ARXPS measurements and zeta potential indicate that the thiols were chemically bonded to the surface of the plasma treated polymers and that the thiols mediate subsequent grafting of Pt and Pd nanoparticles. Generally, EDS revealed that Pt nanoparticles are homogeneously distributed over the whole surface and Pd nanoparticles tend to aggregate slightly. In case of L929 cells, the chemical anchoring of Pt nanoparticles to PET surface significantly enhanced cell adhesion and proliferation compared to pristine PET. (C) 2016 Elsevier B.V. All rights reserved.