CONICET | Buscador de Institutos y Recursos Humanos

Introduction: Metallic materials are the most used materials as orthopaedic or dental implants for their excellent mechanical properties. However they are not able to create a natural bonding with the mineralized bone and they could release metallic particles that could finally end in the removal of the implant [1,2]. One way to avoid these effects is to protect the metallic implant with a biocompatible coating [3,4]. In this work there are analyzed two kinds of protective organic-inorganic coatings made by sol gel technique with the adding of silica particles in order to increase the barrier effect of the coating and glass-ceramic particles with the aim of generating bioactivity. Materials and Methods: Coatings were prepared form the hydrolysis and policondensation of tetraethoxysilane TEOS (99%, Aldrich) and methyltriethoxysilane , MTES (98%, Aldrich) adding SiO2 coloidal (40 g/l, LEVASIL 200A, Bayer). Silica colloidal concentration was varied from 10 to 30% in mols. Bioactive glass ceramic particles(VC) were obtained from a SiO2-CaO-P2O5 glass system followed by a heat treatment for two hours at 1050 ºC in air atmosphere in order to crystallize apatite and wollastonite as crystalline fases. Coatings were deposited on soda-lime glass slides and stainless steel (316L) sheets. Samples were degreased, hand washed with distilled water, and rinsed in ethanol. Coatings were obtained at room temperature by dip-coating using a withdrawal rate of 30 cm.min-1, dried at room temperature for 30 minutes, and heat treated for 30 min at 450oC in electric furnace. Two kind of coatings were made: 1) first layer of TEOS-MTES + SiO2 10% and second layer TEOS-MTES + SiO2 10% + 10% VC 2) First layer of TEOS-MTES + SiO2 30% and second layer TEOS-MTES + SiO2 10% + 10% VC The coating homogeneity and adherence was evaluated by scanning electron microscopy (HITACHI S-4700 field emission). Coating thickness was measured on glass substrates after densification by using a profilometer (Talystep, Taylor-Hobson, UK) on a scratch. The thickness was also studied by SEM using a cross section of the coating. Samples (coated and bared ones) were immersed in simulated body fluid (SBF [5]) Electrochemical assays were conducted in a Solartron 1280B electrochemical unit. A conventional three electrode cell was used with a saturated calomel electrode (SCE; Radiometer) as reference electrode and a platinum wire as counter electrode. Potentiodynamic polarization curves were conducted from the corrosion potential (Ecorr) to 1V at a sweep rate of 0.002 V s-1. Electrochemical spectroscopy impedance (EIS) test were registered at the Ecorr with an amplitude of 0.005 V rms sweeping frequencies from 20000 to 0.01 Hz. Impedance data fitting was performed using Zplot software [6]. Bioactivity was evaluated after 30 days of immersion in SBF at 37 ºC by means of XPS analysing Ca and P signal as the main components of the osseous tissue. Results and discussion Coatings were homogeneous when observed by microscopy. Final thickness was around 3 microns. Coatings seem to offer a good protection to the substrate and degradation was not important in the studied immersion period, although a residual porosity could be observed. Amorphous hydroxyapatite (aHAp) deposited on the samples after 30 days of immersion in simulated body fluid (SBF) was detected on the samples and its presence is considered as a first signal of bioactivity. Ca and P signals are analysed and apatite is more evident in coating 1 than 2. Conclusions: · Coatings offer good corrosion protection to the substrate. · Silica nanoparticles increase coating barrier effect · aHAp is detected onto the coatings showing the first signal of their bioactivity.