Corrosion improvement of surgical grade stainless steel by sol-gel hybrid coatings containing SiO2 nanoparticles and glass-ceramic particles

SILVIA M. CERÉ; SERGIO A. PELLICE; WIDO H. SCHREINER; ALICIA DURÁN; JOSEFINA BALLARRE

Niza, Francia

Congreso; 61st Annual Meeting of the International Society of Electrochemistry ISE; 2010

Among the materials used as orthopaedic devices, metals are the most used due to their excellent mechanical properties. Nevertheless they are no able to make a natural bonding with the existing bone, and it is necessary to fix them with external devices or acrylic cement. Besides, metals can release particles to the surrounding area, leading to the final removal of the prosthesis. The protection of AISI 316L stainless steel used as permanent implant applying a hybrid organic-inorganic sol-gel made coating is one way to modify the surface of metals, acting as barrier for ion migration and being this coatings potential holders for different kind of functional particles. This work present coatings made by the sol-gel method containing tetraethoxysilane, methyl-triethoxysilane and different amount of silica nanoparticles as precursors by dipping. The coatings are made with a two layer system: the inner containing either with 10 or 30% of silica nanoparticles and the upper one with 10%. This last film is also added with 10%w of glass-ceramic particles. The addition of SiO2 colloidal particles to the sol is thought to give films with bigger thickness than the ones without nanoparticles and the addition of bioactive glass-ceramic particles to the external layer generates the coatings the ability to bone with the existing bone. The coatings with 10% SiO2 particles in the inner layer present better corrosion resistance than the coatings with 30% of silica in the internal layer. The electrochemical behavior of the coatings can be explained considering the reactions that take place into the defects. There is an OH- release as a product of the cathodic reaction en slightly basic aqueous media in presence of oxygen, which leads to local basification of the medium. The nanoparticles present in the coatings can react with the OH- leading to silicate formation. These silicates can react with Na+ and K+ present in the SBF, creating soluble silicates that conduct to the progressive deterioration of the film or with other insoluble silicate compounds that can contribute to the progressive filled of the coatings defects. When glass-ceramic particles are added to the outer layer, the particles react with the SBF media to deposit hydroxyapatite (HAp). The coatings with high amount of silica nanoparticles in the inner layer presented less HAp deposition on the coatings cracks due to the deposition of silicates competing with the Hap deposition. The coating with 10% of silica nanoparticles and glass-ceramic particles in the outer layer presented the optimums behavior, being both protective and bioactive.