Silvia Ceré

Improving the osteointegration and bone–implant interface by incorporation of bioactive particles in sol–gel coatings of stainless steel implants

In this study, we report a hybrid organic-inorganic TEOS-MTES (tetraethylorthosilicate-methyltriethoxysilane) sol-gel-made coating as a potential solution to improve the in vivo performance of AISI 316L stainless steel, which is used as permanent bone implant material. These coatings act as barriers for ion migration, promoting the bioactivity of the implant surface. The addition of SiO(2) colloidal particles to the TEOS-MTES sol (10 or 30 mol.%) leads to thicker films and also acts as a film reinforcement. Also, the addition of bioactive glass-ceramic particles is considered responsible for enhancing osseointegration. In vitro assays for bioactivity in simulated body fluid showed the presence of crystalline hydroxyapatite (HA) crystals on the surface of the double coating with 10mol.% SiO(2) samples on stainless steel after 30 days of immersion. The HA crystal lattice parameters are slightly different from stoichiometric HA. In vivo implantation experiments were carried out in a rat model to observe the osteointegration of the coated implants. The coatings promote the development of newly formed bone in the periphery of the implant, in both the remodellation zone and the marrow zone. The quality of the newly formed bone was assessed for mechanical and structural integrity by nanoindentation and small-angle X-ray scattering experiments. The different amount of colloidal silica present in the inner layer of the coating slightly affects the material quality of the newly formed bone but the nanoindentation results reveal that the lower amount of silica in the coating leads to mechanical properties similar to cortical bone.

In vivo and in vitro evaluation of vitreous coatings on cobalt base alloys for prosthetic devices

Abstract This work describes the electrochemical and biological response of wires of CrCoMo surgical alloys (F75) covered by two layers of SiO2 coating prepared by sol–gel to evaluate their properties in simulated body fluids and implanted in Lew rats for the in vivo evaluation. Wires were coated by a single layer of hybrid silica (that means that the coating contains Si–CH3 groups) covered by another similar layer containing a suspension of bioactive glass-ceramic particles in the system CaO–SiO2–P2O5 to provide fixation to bone. Standard electrochemical tests were conducted for the in vitro measurements and showed smaller current density for the covered samples than for the uncovered ones after 30 days of immersion. For the in vivo tests the coated wires were inserted in the tibia cortical bone by a press fit technique in Lew rats and analysed after 53 days of being implanted. We observed that none of the wires created an inflammatory response. Moreover the covered wires developed neo formed bone in the surroundings of the samples made of collagen with a vascular development. Uncovered wires did not develop new histionic structure.

Surface redox catalysis and reduction kinetics of hydrogen peroxide on copper–nickel alloys

Abstract The electrochemical reduction of hydrogen peroxide on the copper-nickel alloys Cu90Ni10 and Cu70Ni30 in 0.1 M borax has been investigated. The results have been analysed on the basis of a chemical–electrochemical mechanism involving a surface Cu(I)/Cu(II) redox couple. The electrochemical step corresponds to the reduction of Cu(II) followed by the chemical reaction of Cu(I) with hydrogen peroxide. The rate of hydrogen peroxide reduction is strongly dependent on the rate constant of the chemical step. The potential dependence of the surface coverage by Cu(I) species accounts for the large values of the Tafel slopes. The catalytic effect of Cu(I) is similar to that of AuOH noted previously for the reduction of H 2 O 2 on gold. Ellipsometric measurements also indicate the presence of an oxide/hydroxide layer at the interface at potentials very negative with respect to bulk Cu 2 O reduction.

Potential dependence of the optical properties of the copper | aqueous borax interface

Abstract The potential dependence of the optical properties of a copper surface at potentials where CuO and Cu 2 O are reduced has been studied by in situ ellipsometry in 0.1 M borax. It is shown that a thin layer of a copper(I) oxide remains on the surface even after extensive reduction. It is proposed that these oxide films play an important role in the kinetics of oxygen and hydrogen peroxide reduction.

Electrochemical evaluation of resistance to localised corrosion of vitreous coatings containing particles applied on metallic substrates for biomedical applications

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passive oxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can cause fracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the corresponding decrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallic ions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue. This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coating obtained by sol‐gel. The silica sol‐gel coating contains bioactive glass ceramic and vitreous particles of the system CaO‐ SiO2‐P2O5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating is evaluated in simulated body fluid (SBF) pH 7.31 at 37 jC. As cobalt base alloys are susceptible to crevice attack, coated pieces are also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations that develop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization and electrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glass ceramic particles showed lower passive current densities than those with monolayers. The coating improves the protection potential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but the protection potential shifts to potentials more active than those measured in the neutral SBF. D 2002 Elsevier Science B.V. All rights reserved.

Enhancing low cost stainless steel implants: bioactive silica-based sol-gel coatings with wollastonite particles

A hybrid organic-inorganic sol-gel coating with the addition of wollastonite particles is used as a potential solution to improve performance of low cost AISI 316L stainless steel. This work is focused on characterising the coatings by studying their synthesis and deposition, electrochemical, and in vitro and in vivo response. The coated implants presented in vitro Ca/P-rich apatitic precursors phases on their surface and acceptable electrochemical behaviour. The in vivo response regarding bone formation seems to be excellent either with the implant in contact with bone marrow, in contact with the endostium or in contact with the trabecular bone. The bioactive and regenerative responses of bone tissue to the TEOS-MTES-wollastonite system over-compensate the coating deterioration reaction, making these coatings as a good way to improve osseo-integration of stainless steel for long term use implants.

Effect of anodization on the surface characteristics and electrochemical behaviour of zirconium in artificial saliva

The paper is focused on elaboration of ZrO2 films on pure zirconium via anodizing in phosphoric acid with and without fluoride at constant potentials of 30 V and 60 V. The structure and composition of the films were investigated using scanning electronic microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The composition of the oxides formed at both potentials can be identified as monoclinic ZrO2. In addition to Zr and O, the layers formed in phosphoric acid contain phosphorus originating from the phosphoric acid. When the phosphoric acid solution contains NaF, fluorine is also incorporated into the oxide layer. The oxides formed at a higher voltage have greater roughness than those formed at 30 V. Anodized samples exhibit smaller current densities during anodic polarization compared to the as-received zirconium covered with native oxide.

Coatings Containing Silica Nanoparticles and Glass Ceramic Particles Applied onto Surgical Grade Stainless Steel

Metals 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. A promising alternative to avoid those effects is to protect the implant with a biocompatible coating. 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 (GC) particles with the aim of generating bioactivity. X-ray photoelectron spectroscopy (XPS) and electrochemical techniques were used to analyze the bioactive and protective response of this silica reinforced coatings with the adding GC particles applied on surgical grade stainless steel.

In vitro and in vivo characterization of anodised zirconium as a potential material for biomedical applications

In vitro studies offer the insights for the understanding of the mechanisms at the tissue-implant interface that will provide an effective functioning in vivo. The good biocompatibility of zirconium makes a good candidate for biomedical applications and the attractive in vivo performance is mainly due to the presence of a protective oxide layer. The aim of this study is to evaluate by in vitro and in vivo approach, the influence of surface modification achieved by anodisation at 30 and 60V on zirconium implants on the first steps of the osseointegration process. In this study cell attachment, proliferation and morphology of mouse myoblast C2C12-GFP and in mouse osteoprogenitor MC3T3-E1 cells was evaluated. Also, together with the immune system response, osteoclast differentiation and morphology with RAW 264.7 murine cell line were analysed. It was found that anodisation treatment at 60V enhanced cell spreading and the osteoblastic and osteoclastic cells morphology, showing a strong dependence on the surface characteristics. In vivo tests were performed in a rat femur osteotomy model. Dynamical and static histological and histomorphometric analyses were developed 15 and 30days after surgery. Newly formed bone around Zr60V implants showed a continuous newly compact and homogeneous bone just 15 after surgery, as judged by the enhanced thickness and mineralization rate. The results indicate that anodising treatment at 60V could be an effective improvement in the osseointegration of zirconium by stimulating adhesion, proliferation, morphology, new bone thickness and bone mineral apposition, making zirconium an emerging candidate material for biomedical applications.

Anodisation and Sol–Gel Coatings as Surface Modification to Promote Osseointegration in Metallic Prosthesis

Orthopaedic devices for permanent implants require short term fixation and fast bone attachment and healing. Superficial modification of surgical implants is often used as a tool to generate a surface that besides being protective could also allow the integration of the metal to the human body, creating a “bioactive” surface that has the ability of creating a natural bonding between the metal surface and the existing bone. One way of achieving this surface modification is by means anodisation since an increase in the thickness and changes in the topography of the native oxide formed on metals can produce an improvement in bone response. Other possibility in the surface modification of the metallic implants is the coatings with organic-inorganic ceramic or glassy coatings as a way to improve the implant performance.The aim of this charter is review the surface modifications produced on orthopaedic and dentistry metallic materials by anodisation and by hybrid coatings by sol gel technique with the aim of promoting both corrosion resistance in physiological fluids and bioactivity.