Hybrid materials combining polyethylene terephthalate and different types of cells (endothelial and osteoblastic cells) have been developed thanks to the covalent grafting of different densities of RGD containing peptides onto the polymer surface. Biomimetic modifications were performed by means of a three-step reaction procedure: creation of COOH functions, coupling agent grafting and the immobilization of the RGDC peptides. High resolution m-imager was used to evaluate RGD densities (varying between 0.6 and 2.4 pmol/ mm 2 ) and has exhibited the stability of the surface grafted peptides when treated in harsh conditions. The efficiency of this route for biomimetic modification of a PET surface was demonstrated by measuring the adhesion of MC3T3 and HSVEC cells and by focal adhesion observation. Results obtained prove that a minimal RGDC density of 1 pmol/mm 2 is required to improve MC3T3 and HSVEC cells responses. Indeed, cells seeded onto a RGDC-modified PET with a density higher than 1 pmol/mm 2 were able to establish focal adhesion as visualized by fluorescence microscope compared to cells immobilized onto unmodified PET and RGDCmodified PET with densities lower than 1 pmol/mm 2 . Moreover, the number of focal contacts was enhanced by the increase of RGDC peptide densities grafted onto the material surface. With this study we proved that the density of peptides immobilized on the surface is a very important parameter influencing osteoblast or endothelial cell adhesion and focal contact formation.