This work is an investigation of the electrografting of in situ generated 4-sulfonic acid phenyldiazonium salt (PD-SO 3 H) 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-SO 3 H in this work. Results show the successful electrografting of PD-SO 3 H and the preservation of the TiO 2 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-SO 3 H 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.

Coating Nitinol (NiTi) surfaces with a polymer layer has become very appealing in the past few years owing to its increased attraction in the biomedical field. Although its intrinsic properties helped ensure its popularity, its extensive implementation is still hampered by its nickel inclusion, making it sensitive to pitting corrosion and therefore leading to the release of carcinogenic Ni ions. Among all recent ways to modify NiTi surfaces, elaboration of self-assembled monolayers is of great interest as their high order confers a reinforcement of the metal surface corrosion resistance and brings new functionalities to the metal for postmodification processes. In this work, we compare the electroassisted and thermally assisted self-assembling of 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid (BUPA) to the classical immersion process on NiTi surfaces initially submitted to a hydrothermal treatment. Among all tested conditions, the electroassisted grafting of BUPA at room temperature appears to be the most promising alternative, as it allows grafting in very short times (5-10 min), thus preventing its degradation. The thus-formed layer has been proven to be sufficient to enable the surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-(dimethylamino)ethyl methacrylate.

Nitinol (NiTi), one of the most important alloys for biomedical applications, is still hampered by its surface nickel inclusions, making it sensitive to pitting corrosion and leading therefore to the release of potentially carcinogenic Ni 2+ ions. In this work, we assess the impact of the combination of electrografted mixed self-assembled monolayers (SAMs) on NiTi followed by a polymer coating formed by surfaceinitiated atom transfer radical polymerization (SI-ATRP). The molecular ratio of 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid (BUPA) to 11-decylphosphonic acid (C 10 P) on the electroassisted elaboration of the (BUPA/C 10 P)-NiTi-SAMs has been optimized. A small amount of BUPA (20%) appears to be the most promising condition, as it provides an efficient corrosion resistance and promotes the SI-ATRP of 2-methacryloyloxyethyl methacrylate (MPC). This confers to the surface hydrophilic properties and corrosion resistance close to those NiTi-SAMs when long polymerization times are used (‡ 6 h).