Functionalization of Nitinol surface toward a versatile platform for post-grafting chemical reactions

Nitinol is a material of great interest given its many possible applications, especially in the biomedical field. However, due to its high nickel content and the cytotoxic nature of nickel (II), a great attention has been paid to the improvement of Nitinol corrosion resistance and the limitation of Ni2+ ions release but also to the improvement of the material–biological environment interaction. In this work, we report on the modification of Nitinol by electrografting of 1,4-carboxybenzene diazonium and by formation of a 11-phosphoundecanoic acid monolayer as well as on the assessment of the efficiency of these coatings to act as a platform for post-grafting chemical reactions. The electrografting of 1,4-carboxybenzene diazonium leads to the formation of a non-compact hydrophilic multilayer with some solvent molecules and electrolyte cations entrapped in it and has a negative impact on the Nitinol corrosion resistance properties. The grafting of 11-phosphoundecanoic acid on Nitinol leads to the formation of a monolayer showing less pronounced hydrophilic properties than the electrografted carboxybenzene layer does and a less negative impact on the Nitinol corrosion resistance properties. The post-grafting esterification reaction has been shown to be more efficient when carried out on an 11-phosphoundecanoic acid monolayer than on the carboxybenzene electrografted layer.

► 1,4-Carboxybenzene diazonium electrografting forms a non-compact hydrophilic multilayer.
► 1,4-Carboxybenzene diazonium electrografting decreases Nitinol corrosion resistance.
► 11-Phosphoundecanoic acid grafting leads to the formation of a monolayer.
► 11-Phosphoundecanoic monolayer has a low impact on the Nitinol corrosion resistance.
► Post-grafting reaction more efficient on a 11-phosphoundecanoic acid monolayer.