Anodization and sol gel coatings as surface modification to promote osseointegration in metallic prosthesis

JOSEFINA BALLARRE; ANDREA GOMEZ SANCHEZ; CERE, SILVIA

Modern Aspects of Electrochemistry- Issue: Biomedical and Pharmaceutical Applications of Electrochemistry

SPRINGER

Año: 2016;

Orthopedic devices for permanent implants require short term fixation and fast bone attachment and healing. Also they are required to have excellent mechanical properties in load bearing sites and to be corrosion resistant. Metallic alloys used in surgery share, in common, high mechanical resistance (Hastings 1980) and high corrosion resistance in physiologic media mainly due to the formation of a passive oxide film that reduces the corrosion rate by blocking the transport and the possible migration of metallic ions from the base metal to the nearby tissue (Hanawa 2004). Surface 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 create a natural bonding between the metal surface and the existing bone.(Im et al. 2007; Krupa et al. 2003; Rodríguez et al. 2008; Simmons et al. 1999; Yang et al. 2004). Increasing bioactivity while keeping low corrosion is one the main objectives of most of the research being performed on metallic materials for permanent implant applications. It has been extensively proved that the success or failure of the osseointegration process is determined by the surface characteristics in different space length scales (Barrere et al. 2004; Mendonca et al. 2008; Navarro et al. 2008), and those materials where osseointegration occurs, have a lower implant replacement rate (Navarro et al. 2008). The development of porous surfaces, are attempting to solve the adherence problems between the implants and the adjacent tissue. One way of achieving this surface modification in order to contribute to the osseointegration process is by means anodization. Anodization is the electrochemical route that conducts to the formation of an oxide grown by an anodic process. The oxide thickness formed by anodization varies from a few nanometers to a hundred of micrometers, changing the surface topography, the surface pore configuration, the crystal structure of the oxide formed and the chemistry of the surface since it can incorporate anions from the electrolyte in their structure (Sul et al. 2001). (Otsuki et al. 2006; Simmons et al. 1999). It has been demonstrated that an increase in the thickness and changes in the topography of the native oxide formed on metals, can produce an improvement in bone response (Albrektsson et al. 2000; Sul et al. 2002). Surface properties such as topography, roughness, oxide thickness and microstructure, oxide chemistry, can be varied controlling anodizing variables as electrolyte solution, current density, potential, temperature among others (Sanchez et al. 2011; Sul et al. 2002). Other possibility in the surface modification of the metallic implants are the coatings with organic-inorganic ceramic or glassy coatings as a way to improve the implant performance (Durán et al. 2004). It has been demonstrated that inorganic - hybrid SiO2 coatings, obtained from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) improve the corrosion behaviour of the AISI 316L stainless steel in biological environments (Ballarre et al. 2007; Checmanowski and Szczygiel 2008; Chou et al. 2003). The hybrid layers of TEOS and other silanes are not bioactive per se but if the coatings are also functionalized with a bioactive ceramic or glass-ceramic from the CaO-SiO2-P2O5 system, it has been proved that the HA rate can be maximized(Höland 1997; Kokubo et al. 1992; Peitl et al. 2001). Silica is also known as a natural catalyst for hydroxyapatite formation (HA: Ca10 (PO4)6(OH)2), showing bioactivity in vitro (Beck Jr et al. 2012; Hing et al. 2006).The aim of this charter is review the surface modifications produced on orthopaedic and dentistry metallic materials by anodization and by hybrid coatings by sol gel technique with the aim of promoting both corrosion resistance in physiological fluids and bioactivity.