Development and analytical characterization of cysteine-grafted polypyrrole films electrosynthesized on Pt- and Ti-substrates as precursors of bioactive interfaces

The grafting of cysteine to polypyrrole(PPY)-coated platinum and titanium s ubstrates has been investigated with the aim of developing innovative bioac tive materials of interest for bone implants. Polypyrrole has been chosen a s the coating polymer because of its suitability to be electrochemically gr own directly onto metallic substrates, of any shape and dimension, leading to remarkably adherent overlayers. The effectiveness of grafting was monito red by X-ray photoelectron spectroscopy (XPS) which showed the presence of aminoacid residues onto the polymer surface. Information obtained by an acc urate curve fitting of significant regions in the spectra (Cls, N1s, and Ol s signals) and by a cross-check of peak area ratios, before and after the g rafting process, gave evidence that cysteine forms covalent bonds to pyrrol e rings, preferentially in B-positions, via the sulfydryl group, leaving bo th amino and carboxylic functionalities available for further chemistry. The surface density of cysteine residues was evaluated by microgravimetric measurements performed by the electrochemical quartz crystal microbalance a nd was found suitable for the exploitation of these modified surfaces as bi oactive systems. Some preliminary results are reported on the adhesion of neonatal rat calva rial osteoblasts onto titanium substrates after coating by a PPY film modif ied by a polypeptide having cysteine as a terminal residue and containing t he Arg-Gly-Asp aminoacid adhesive sequence.