Polyelectrolyte Multilayers Deposition on Nitinol Modified by In Situ Generated Diazonium in Gentle Conditions

This work is an investigation of the electrografting of in situ generated 4-sulfonic acid phenyldiazonium salt (PD-SO₃H) on Nitinol followed by layer-by-layer (LBL) deposition of polyelectrolyte (chitosan and alginate) multilayers (PEM). Nitinol is interesting for many biomedical applications. A great deal of attention has thus been paid to its surface modification in order to impart and/or improve its surface properties. This can be achieved using PEM deposition which requires an adhesion promoter i.e. PD-SO₃H in this work. Results show the successful electrografting of PD-SO₃H and the preservation of the TiO₂ surface layer (which provides its biocompatibility to Nitinol) allowed by the gentle conditions used for the in situ generation. Nitinol corrosion resistance has been shown to be preserved. Based on XPS analysis, PD-SO₃H has been shown to be grafted in its deprotonated form and hypothesis of C-O-M and C-N=N-O-M covalent bonds formation between the grafted layer and the Nitinol surface could be made. It can therefore act effectively as adhesion promoter for PEM deposition as confirmed by the deposition, accumulation and alternation of the deposited chitosan and alginate layers. PEM further improve Nitinol corrosion resistance and its resulting hydrophilicity has been shown to be controlled by the last deposited layer.