Antibacterial titanium dioxide coatings for joint prosthesis

A. D’Agostino, P. Tarsini, G. Candiani, R. Chiesa, L. De Nardo
Polytechnic University of Milan,
Italy

Keywords: sol-gel technique, coatings, antibacterial activity

Summary:

Joint prosthesis infections are one of the main causes of illness and decease in clinical environment(1). In fact the surface of medical devices such as hip prosthesis or knee prosthesis represent an ideal substrates for the development of bacterial infections with a huge impact on public health in terms of mortality, morbidity and economic cost. The most important issue in this type of infections is the ability of microbial populations to produce biofilms. Biofilms are microorganisms aggregates, characterized by complex biological interactions and a strong tendency towards surface adhesion, protected by a polysaccharide shell. These features render the biofilms resistant to common antibiotics. For such reasons, in the last years great efforts have been made to act on modification of surface properties in order to obtain smart biomedical devices capable of exerting an antibacterial activity. Many strategies have been studied like the incorporation of antibiotics and antiseptics(1); organic antimicrobial agents; use of innovative anti-adhesive polymer coatings or chemical-physical surface modification techniques. Among these, sol gel technique(2) could represent a powerful tool to incorporate inorganic antimicrobial agents like silver, largely investigated in literature for its antibacterial properties(3), and gallium, which has recently attracted great scientific interest(4). In this work sol gel technique has been employed to obtain a titanium dioxide coatings doped with silver and gallium ions with the goal of minimizing the adhesion of bacterial colonization on the cylindrical samples of cobalt-chromium-molybdenum alloy widely used for hip and knee prosthesis components. Two types of samples has been used: ones with a blasted surface, the other ones with a titanium plasma-spray treated surface required for a better osseointegration. Firstly the optimization of chemical synthesis parameters of sol formulation has been investigated (use of different carboxylic acids as chelating agents, reaction temperatures). Dynamic Light Scattering measurements have been taken to estimate the hydrodynamic diameter of particles in solution before the deposition. Then substrates were immersed in doped sols, in which the antibacterial ions in form of salts have been added ([0.01 M] of AgNO3 or [0.01] M of Ga(NO3)3 *H2O), using a dipper and thermally treated to achieve the desired coating. Obtained samples have been fully characterized through XRD analysis to understand the crystallinity of titanium layer; by SEM-EDS measures to study composition, homogeneity of coating and also demonstrate incorporation of antimicrobial agents inside it; by GDOES analysis to evaluate thickness of coating. Furthermore, ICP test have been performed to quantify concentrations of antibacterial ions. In addition changes in morphology and surface wettability before and after deposition were studied employing contact angle and roughness measurements. Preliminary antibacterial test have been assessed to understand behavior of coated and not coated sample against proliferation of Staphilococcus Aureus after 24 hours. Even if further evaluations about cytotoxicity of coated substrates are required, all results encourage use of this simple approach for surface modifications of medical devices such joint prosthesis in Co-Cr alloys.