Influence of gas nitriding of Ti6Al4V alloy at high temperature on the adhesion of Staphylococcus aureus M. Isabel Sarró a , Diego A. Moreno a, ⁎ , Carlos Ranninger a , Eleanor King b , José Ruiz c a Universidad Politécnica de Madrid, Departamento de Ingeniería y Ciencia de los Materiales, Escuela Técnica Superior de Ingenieros Industriales, José Gutiérrez Abascal, 2, E-28006 Madrid, Spain b Department of Materials, Imperial Collage of Science, Technology and Medicine, Prince Consort Road, London SW7 2BP, United Kingdom c Centro Nacional de Investigaciones Metalúrgicas (CSIC), Avda. de Gregorio del Amo, 8, E-28040 Madrid, Spain Received 5 October 2004; accepted in revised form 22 May 2006 Available online 7 July 2006 Abstract In this in vitro study, we investigated the influence of titanium nitride (TiN) treatments on the Staphylococcus aureus colonisation and biofilm formation on Ti6Al4V alloy at different times. The development of biofilm in static tests was carried out in a TSB culture medium at 37 °C, for 12, 24, 48 and 72 h. Bacterial adhesion on nitrided titanium alloy was analysed by both epifluorescence microscopy and scanning electron microscopy. The results revealed that the number of attached bacteria, their viability, and distribution were different for nitrided alloys than for the control group (non-nitrided alloys). © 2006 Elsevier B.V. All rights reserved. Keywords: Titanium alloy; Surface treatment; TiN; Bacterial adhesion; Biofilm 1. Introduction Titanium and titanium alloys are widely used in a variety of medical applications, where the combination of mechanical and chemical properties is of crucial importance. The increased use of titanium alloys, especially Ti6Al4V, is due to its low density, its excellent mechanical and anti-corrosive properties, and its biocompatibility [1–5], compared to stainless steel or cobalt- chrome alloys [6,7]. However Ti6Al4V have very poor tribological properties, for this reason, many techniques have been developed to improve their wear resistance properties. For the last decades, numerous artificial prosthesis with titanium and alloys as Ti6Al4V with different types of coatings or surface treatments has been deve- loped [8–13]. One of these surface modifications is made up of a titanium nitride (TiN) layer favouring nitrogen diffusion into the surface of the material. This method modifies the surface of the alloy and improve the wear resistance, and the tribological properties of titanium alloys [14–18]. The artificial prosthesis are intend for long-term or permanent implantation, but the influence of these coatings in bacterial colonisation is poorly documented, and in many cases these prosthesis have to be removed for different reasons, most of them related to infections [19,20]. The basis of the pathogenic mechanism of these infections in biomaterials used for the implants is related to the ability of some microorganisms to attach to the surfaces and form biofilms [21–24] in which the bacterial cells exhibit increased resistance to anti- microbial agents and the host immune system [25,26]. Biofilm infections typically showed recurring symptoms, after cycles of antibiotic therapy [27], until the sessile population with the prosthesis is removed from the body [28]. Normally, microorganisms of the Staphylococcus group [29] are the most common etiological agent in nosocomial infections of prostheses. Staphylococcus aureus has a marked preference for metallic prostheses, such as titanium alloys (Ti6Al4V) [20,23] whereas Staphylococcus epidermidis mostly affects non-metallic implants, such as plastic endovascular catheters [20,30]. These microorganisms are classified as opportunists due to their low pathogenic capacity, but when they are associated to biomater- ials, they can cause serious infections [31]. For these reasons, Surface & Coatings Technology 201 (2006) 2807 – 2812 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: +34 91 336 3164; fax: +34 91 336 3007. E-mail address: diego.moreno@upm.es (D.A. Moreno). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.05.023