Protection and functionalization of AISI 316L for orthopedic implants

SILVIA M. CERÉ; SHEILA OMAR; JOSEFINA BALLARRE

Troia

Congreso; Congreso de Métodos Electroquímicos EMCR; 2015

EMCR

Orthopedic devices for permanent implants require short term fixation and fast bone attachment and healing. Surface modification of surgical implants is often used as a tool to generate a protective barrier along with the possibility of providing integration of the metal to the human body. This integration can be enhanced creating a bioactive surface able to produce a natural bonding between the metal and the existing bone. One possibility in the surface modification of metallic implants is the creation of organic-inorganic hybrid coatings as a way to improve the prosthesis performance. It has been demonstrated that SiO2 based coatings, obtained from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) improve the corrosion behavior of the AISI 316L stainless steel in biological environments. The hybrid layers of TEOS and other silanes are not bioactive by themselves but they can be functionalized with particles that can induce bioactivity. It has been proved that coatings functionalized with a bioactive ceramic or glass-ceramic from the CaO-SiO2-P2O5 system can maximized the hydroxyapatite deposition rate. This work presents the synthesis and deposition of sol-gel coating, with an initial solution containing TEOS, MTES and colloidal silica nanoparticles, applied on AISI 316L stainless steel by dip-coating as a first layer with the aim of providing the corrosion protection of the substrate. A heat treatment of 30 min at 450 ºC was performed to consolidate this protective layer. On the top of this coating a potentially bioactive glass (58S) made also by sol gel method with TEOS, triethyl phosphate (TEP) and calcium nitrate as precursors, was applied by spray technique deposition using comprised air as carrier with a high efficiency filter. This method allows the creation of a wide distribution of particles sizes over the target. A stabilization treatment at 450 ºC for 3 hours was held to ensure the glass formation and nitrate and residues elimination. Coatings were characterized by profilometry and optical and electronic microscopy. The surface integrity and corrosion resistance of the coatings in time is analyzed by electrochemical tests together with the solubilization of the particles in simulated body fluid (SBF).