Electrochemical evaluation of multilayer silica-metacrylate hybrid sol-gel coatings containing bioactive particles on surgical grade stainless steel

J. BALLARRE,; D.A. LÓPEZ,; NATALY C. ROSERO-NAVARRO; A. DURÁN; M. APARICIO; S. CERÉ.

SURFACE AND COATINGS TECHNOLOGY

Elsevier

Año: 2008 vol. 203 p. 80 - 86

0257-8972

Metallic materials are the most used materials as orthopaedic or dental implants because of their excellentmechanical properties. However they are not able to create a natural bonding with the mineralized bone andoccasionally suffer localized corrosion. This work describes the electrochemical behaviour of a system ofcoatings with the addition of bioactive particles of the system SiO2–CaO–P2O5, that enhance the abilities ofthe implant to make an union with the existing bone and to resist the extreme environment that are exposedto. The coatings were obtain from two kind of sols that were made by sol–gel process: one, usingtetraethoxysilane (TEOS) and methyl triethoxysilane (MTES) as precursors, and the other using hydroxyethylmethacylate (HEMA), tetraethoxysilane (TEOS) and 3-methacryloxypropyl-trimethoxysilane (γMPS) [TMH]as precursor. Coatings were made in two layers. The inner layer was prepared either using TEOS and MTES(that had already shown good anticorrosion properties), or TMH. The top layer was made with TMH with theaddition of 10% in weight of small (diameter less than 20 μm) or big (more than 20 μm) bioactive particles.The samples were tested in vitro by polarization curves and electrochemical impedance spectroscopy (EIS)assays. The samples with the two kind of coatings seem to have a protective behaviour after 30 days ofimmersion due to the compact TEOS–MTES inner layer. The big particles placed in the outer layer showed adissolution rate similar to the rate of deposition of the amorphous hydroxyapatite (aHAp) at the surface,blocking the entrance of the electrolyte, avoiding it to reach the substrate. The TMH coatings with smallparticles present a similar behaviour to the naked material, allowing the electrolyte to reach the metal. Thedual coating with this kind of particles has similar characteristics, with a “sponge-like” behaviour, and theinner coating probably develops flaws due to the fast dissolution of the small particles placed in the upperlayer.