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 substrates has been investigated with the aim of developing innovative bioactive materials of interest for bone implants. Polypyrrole has been chosen as the coating polymer because of its suitability to be electrochemically grown directly onto metallic substrates, of any shape and dimension, leading to remarkably adherent overlayers. The effectiveness of grafting was monitored by X-ray photoelectron spectroscopy (XPS) which showed the presence of aminoacid residues onto the polymer surface. Information obtained by an accurate curve fitting of significant regions in the spectra (Cls, N1s, and Ols signals) and by a cross-check of peak area ratios, before and after the grafting process, gave evidence that cysteine forms covalent bonds to pyrrole rings, preferentially in B-positions, via the sulfydryl group, leaving both 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 and was found suitable for the exploitation of these modified surfaces as bioactive systems. Some preliminary results are reported on the adhesion of neonatal rat calvarial osteoblasts onto titanium substrates after coating by a PPY film modified by a polypeptide having cysteine as a terminal residue and containing the Arg-Gly-Asp aminoacid adhesive sequence.