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Poster presented at the Fourth International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems that took place in Corfu Island (Greece) during 16-20th June 2013., This study [1] addresses the growth dynamics of nanocrystalline diamond (NCD) films deposited by hot-filament chemical vapor deposition (HFCVD). It is based on the statistical analysis of the evolution of the surface morphology of the films at the mesoscale using atomic force microscopy (AFM). Concepts of the Dynamic Scaling Theory are used focusing on the changes of the growing surface roughness and its lateral correlations with time. In conclusion, the NCD growth dynamics displays two growth regimes., JGB would like to thank the Executive Research Agency of the EU for funding under Marie Curie grant 272448 support by Comunidad Autónoma de Madrid (S2009/PPQ-1642) and Ministerio de Economía y Competitividad (FIS2012-38866-C05-05).

Ni-TiO2nanocomposites coatings with a layer thickness of 21 μm have been obtained by electrocodeposition. Incorporation in nickel matrix of TiO2nanoparticles (10 nm), affects the morphology of the nickel matrix as indicated from scanning electron microscope (SEM) and atomic force microscope (AFM) results. The chemical composition was studied by energy dispersive X-ray spectroscopy (EDS). Analysis by X-ray diffraction (XRD) revealed the inclusion of nickel particles in the matrix and their effect on nickel matrix crystal size changes., This work was financially supported by the research Project IFA-CEA C2-02/01/03/2012.

The biocompatible metals made available for powder injection moulding (PIM) are increasing, and as a result, the PIM process is becoming attractive for manufacturers of medical implants and surgical instruments. In addition, friction and wear properties play an important role in biomaterial applications. This study aimed to systematically investigate the fretting wear properties of 316L stainless steel parts produced by PIM under dry contact conditions. The fretting experiments were performed under gross-slip regime. The influence of a number of fretting test parameters on the friction and wear behaviour was investigated, as the contact frequency, the normal load, and number of reciprocating sliding cycles. Fretting tests were performed against corundum counter bodies. After the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis. The results indicate that wear occurred predominantly by abrasion, plastic deformation, and cracking.

Even though titanium (Ti) has the ability to develop a highly stable passive oxide layer (TiO2) that provides an excellent corrosion resistance; it’s not inert to corrosive attack. Under in vivo conditions, such as in orthopedic and dental implants, a tribological contact may be formed in association with a chemical aggressive environment. Consequently, wear debris and corrosion products or ions can lead to inflammatory reactions, such as osteolysis (bone resorption), provoking peri-prosthetic bone loss and subsequent loosening of the implant/prosthesis [1]. The microbial effect on the corrosion of metallic biomaterials remains unknown. Chang et al. [2] reported an increase on the corrosion behaviour of dental metallic materials in the presence of Streptococcus mutans and its growth byproducts. Moreover, brushing can lead to the production of wear debris, which together with the attachment of microbes can disturb the passivity of the metal oxide. In addition, the organic acids produced by bacteria may reduce the pH, favoring the corrosion and tribocorrosion of implants. The aim of this work was to study the influence of mixed biofilms on the biotribocorrosion behaviour of commercially pure (cp) Ti for dental implants, and the consequent effect of fluoride.

The use of dental implants has been increasing even though failures do occur. The presence of wear debris and oral microorganisms can contribute to infections and jeopardize implant integration. The aim of this work was to study the influence of mixed biofilms in the tribological behaviour of commercially pure titanium for dental implants under different concentrations of fluoride. Samples of titanium with two different surface topographies were used. Mixed biofilms of Candida albicans and Streptococcus mutans were formed on both surfaces at 37 °C in a tryptic soy broth containing mucin, peptone, yeast extract and sucrose. After 8 days, biofilm biomass was analysed by crystal violet staining method. Biofilm biomass was significantly higher for the samples with higher roughness. Some samples with biofilms were analysed under friction (using a force of 100 mN) in an artificial saliva solution (Fusayama) without or with different concentrations of fluoride (30 and 227 ppm). It was verified that the coefficient of friction (COF) decreased in the presence of biofilms. Moreover, samples with more biomass (0.4 μm of roughness) presented the lowest values of COF. Concerning the effect of the presence of fluoride, although there were no significant differences on the COF for 30 ppm, for 227 ppm a transition regimen was observed. These results were confirmed by sample observation under scanning electron microscopy. In conclusion, it can be highlighted that biofilm formation on dental implants can significantly affect the tribological behaviour of titanium, namely, the presence of biofilms reduces the release of wear debris.

The oral cavity is a complex environment where corrosive substances from dietary, human saliva and oral biofilms may accumulate in retentive areas of implant-supported prostheses promoting a corrosion of their surfaces. On the other side, during mastication, micro-movements may occur in artificial joints causing a relative contact motion between surfaces. Both processes result in a tribocorrosion system. The objective of this work is to investigate the in-vitro tribocorrosion behavior of titanium covered by biofilms and immersed in artificial saliva. Reciprocating sliding wear tests coupled with electrochemical techniques were performed at 25 o C on titanium samples covered or not with biofilms. Mixed biofilms of Candida albicans and Streptococcus mutans were grown at 37 oC on titanium surfaces for 9 days in Tryptic Soy Broth medium, containing mucin, yeast extract, peptone and sucrose. The open-circuit potential (OCP) was measured until stabilization in artificial saliva. After that, electrochemical impedance spectroscopy (EIS) measurements were carried out at open circuit potential. Subsequently, sliding tests were performed at normal loads of 0.1, 0.2 and 3 N, at a sliding frequency of 1 Hz, and linear displacement amplitudes of 0.5 and 2 mm using a tribometer equipped with a test viewer software. During the sliding tests, the OCP was constantly monitored. At the end of the sliding test, the OCP was further monitored until stabilization, and another series of EIS measurements was made. Worn and unworn surfaces were inspected by SEM. The detachment of the biofilms was not noticed when low loads were applied, and biofilms appear to have some lubricating effect. However, it was found that acidic substances released from Streptococcus mutans and external substances accumulated into the biofilm might corrode surfaces located below and around the biofilms. At a normal load of 3 N, the biofilms were removed from the contact region by the sliding action, and it was observed that the repassivation rate of titanium covered with biofilms was lower than without biofilms., Fundação para a Ciência e a Tecnologia (FCT), ALBAN, Flemish Science Foundation. Scientific Research Community on Surface Modification of Materials, Programa Alban - Bolsas de Alto Nível da União Europeia para a América Latina

The oral cavity can be considered as an aggressive environment to restorative materials considering that several acidic substances can be retained in the saliva and biofilms as well as loads from mastication and abrasive particles take place in the wear of oral surfaces. The objective of this work is to investigate the in-vitro corrosion and wear in fluoridated artificial saliva and in presence of biofilms. Electrochemical tests of titanium surfaces were performed in artificial saliva containing different fluoride concentrations at 37 oC. Another group of titanium surfaces were prepared to the growth of oral mixed biofilms for 9 days in a specific culture medium. Then, electrochemical tests were carried out with titanium surfaces covered with biofilms in artificial saliva without fluorides. After that, wear sliding tests were performed in the same mediums using a tribometer equipped with a test viewer software. Also, electrochemical measurements were carried during the wear sliding tests. After corrosion-wear tests, worn and unworn surfaces were analyzed by AFM and SEM. A localized corrosion of titanium was only noticed in high fluoride concentration. Therefore, there was a decrease of the corrosion resistance of titanium when the fluoride concentration was increased. Moreover, the presence of biofilms affected harmfully the corrosion resistance of titanium probably due to acids release from the biofilms. However, the wear was decreased when low loads were applied on the biofilms., Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM/67500/2006, Programa Alban - Bolsas de Alto Nível da União Europeia para a América Latina - E06D103407BR, Flemish Science Foundation. Scientific Research Community on Surface Modification of Materials

In the oral cavity, restorative surfaces such as of titanium-based implant systems are in contact with several acidic substances originated from dietary intake and microbial metabolism. During the mastication, a simultaneous corrosion-wear process known by Biotribocorrosion can take place on the surfaces which are in relative contact motion. The objective of this work is to investigate the in-vitro simultaneous corrosion-wear behavior of titanium in the presence of biofilms. Electrochemical tests of titanium surfaces covered or not by mixed oral biofilms (Streptococcus mutans and Candida albicans) were carried out in artificial saliva. After stabilization of open circuit potential of titanium in artificial saliva, reciprocating wear sliding tests were performed against an alumina ball at different loads using a tribometer equipped with a test viewer software. Moreover, electrochemical measurements were carried during the wear sliding tests. Worn and unworn surfaces were analyzed by different SEM techniques. Biofilms decreased significantly the friction of titanium surfaces. However, the presence of biofilms affected negatively the corrosion resistance of titanium probably due to acids release from the biofilms., Comissão Europeia - programa Alban (cod. E06D103407BR), Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM/67500/2006), Flemish Science Foundation. Scientific Research Community on Surface Modification of Materials (WOG-FWO Vlaanderen)

Titanium and titanium alloys have been widely used in orthopeadics and dental implants because of their excellent properties such as low modulus, good fatigue strength, good corrosion resistance and biocompatibility. However, their poor wear resistance still limits their application. When inserted in the oral environment dental implants are under a complex degradation phenomenon as a result of the combined action of chemical and mechanical solicitations, which can result in its failure. The relatively poor wear resistance of titanium may be improved by surface modification, namely by anodic oxidation. Also, as suggested by recent works carried out using animal models, bone regeneration may be enhanced by acting on the surface topography of the implant, essentially if the an oxide is present at the surface. The present study aims to investigate the surface properties of the anodic oxide films created on c.p. Ti. Oxide films were prepared by anodization (potentiostatic mode) in citric acid with different molar concentration and different applied voltages. The thickness, composition, structure and topography of the prepared films were investigated by XRD, RBS, and AFM. Also electrochemical impedance spectroscopy was used to characterize the original native oxide film before anodization, in comparison with the oxide film after anodic oxidation treatment. AFM results demonstrate substantial differences on film topography, with an enhancement on surface roughness. Also, changes on structure, thickness and chemical composition of the anodic oxide layers influences the electrochemical characteristics of the films.

Titanium has been widely used for dental implant applications because their attractive properties such as low Young modulus, good fatigue strength, excellent corrosion resistance and biocompatibility. However it cannot meet all clinical requirements. 1-2 When inserted in the oral environment, dental implants are submitted to a complex degradation phenomena occurring due to the interaction of tribological and corrosive phenomena which can result on its failure. In fact, most of the failures are a result of the combined action of mechanical solicitations (sliding or abrasive wear, erosion, impact, fretting or fatigue processes) and chemical solicitations as a consequence of contact with saliva, cells or bacteria. Consequently, dental implants become part of a tribocorrosion system, and the investigation of the tribocorrosion mechanisms in such systems becomes essential. 3 Recent work has shown that wear resistance of titanium might be improved selectively using the appropriate surface treatment, such as plasma oxidation, which is also often used to enhance the osseointegration process. 4-5 The main aim of this paper is to study the influence of the characteristics of the oxide layers obtained by plasma oxidation on the tribocorrosion behaviour of c.p. Ti intended for the fabrication of dental implants.The plasma oxidation treatment were performed at three different temperatures (300, 450 and 530ºC) and a detailed study of surface topography (Fig. 1), thickness, structure and chemical composition of the oxidized layers was performed. Tribocorrosion experiments were performed using a reciprocating motion pin-on-plate tribometer with an alumina pin as a counterface material in the presence of Fusayama solution. The applied normal force used was 3N, the stroke length 1mm and the displacement frequency was 1Hz. During rubbing the friction coefficient was monitored. Electrochemical techniques were used to follow the evolution of the system during sliding. Each experiment involved an in situ surface cleaning by a cathodic polarization at -900mv during 3 minutes, and after that a potentiostat was used to impose a passive potential to titanium samples. This experiment allows in situ and in real time following of the corrosion kinetics through current measurements. It is important to refer that electrochemical impedance spectroscopy was also used before and after rubbing in order to evaluate the protective character of the oxide film. The influence of the thickness of the oxide layer and of surface roughness on the wear-corrosion behaviour of the material is discussed in detail. Results clearly showed that plasma oxidation treatments have a strong influence on the tribocorrosion behaviour of titanium. Both the corrosion and wear performance of the samples are improved by the increase of the processing temperature. In relation to friction profile no significant differences were found between all samples tested (μ remains between 0.35 and 0.45). Results show that electrochemical techniques yield useful results.

The demand for metallic materials in medical and dental devices is large; metals and alloys are widely used as biomedical materials and are indispensable in the medical field. In particular, toughness, elasticity, rigidity, and, some times, electrical conductivity are essential properties for metallic materials used in medical devices. In dentistry, titanium is used for restorations, orthodontic wires, and dental implants. Materials implanted in the human body are intermittently stressed with loads, which are repeated in a tremendous amount of cycles. During mastication, dental implants are simultaneously subjected to corrosion by the oral environment and to the sliding-wear process by bite forces. Dental wear can be attributed to mastication where the teeth are worn by attrition and abrasion. The main aim of the present study was to investigate the tribocorrosion behaviour of titanium grade 2 in reciprocating sliding conditions in contact with artificial saliva solutions. Particular attention is given to the relationship between mechanical damage and the electrochemical behaviour of the material. Sliding-corrosion experiments were performed using a reciprocating ball-on-flat contact configuration and the open circuit potential was monitored during the test. Also electrochemical impedance spectroscopy was used to obtain a more detailed description of the corrosion mechanisms and to characterise the passive layer that forms on the titanium surface. To reproduce the oral environment around the dental implant, some additives (citric acid, anodic, cathodic and organic inhibitors) were added to simple artificial saliva constituted mainly by NaCl and KCl, and with a pH between 5 and 7. A corundum ball was loaded on the top of the flat rectangular sample at a normal force of 10N. Linear peak-to-peak displacement amplitude of 3 mm at vibrating frequencies of 1 Hz was applied to the tribocorrosion system. The tests were performed for 11160 cycles. The surface roughness and topography of the titanium samples were evaluated prior to testing. In relation to the friction profile, for all solutions, no significant differences were observed. In fact, the aqueous environment used doesn’t have sufficient viscosity to cause changes in the friction behavior. Regarding the weight loss results it is possible to conclude that titanium in artificial saliva solution with citric acid present the high weight lost. Additionally, cathodic and organic inhibitors solutions exposed a higher tendency for corrosion, forming an oxide passive film with lower protection characteristics.

Tribocorrosion refers to a complex degradation of materials occurring due to the interaction between a tribological process and a corrosive environment. From the tribological point of view, the interaction with the material may include sliding or abrasive wear, erosion, impact, fretting or fatigue processes. The environmental solicitation may result from temperature, humidity, liquids or gases in permanent or intermittent contact with the materials. Failure in the metallic part or of the metal/ceramic interfaces existing in dental restorations, such as crowns and bridges, are still relatively frequent. Also, excessive degradation of dental materials is sometimes observed in other dental materials. Most of the failures are due to the simultaneous action of mechanical (wear, fretting and fatigue) and chemical (saliva) solicitations. As a consequence, the investigation of the tribocorrosion mechanisms in such systems becomes essential. Regarding this aspect, in last years particular focus is being given to the exploitation of electrochemical methods as a tool for the investigation of the combined corrosion-wear degradation of the materials. Also, it is known that the mechanical contact geometry is of crucial importance regarding the degradation behaviour. In this work the tribocorrosion behaviour of commercially pure titanium in contact with artificial saliva solutions was investigated. Tests were conducted in a reciprocating sliding geometry with movement amplitudes varying from 200 m (fretting) up to 6 mm (wear), and normal loads between 2 and 10 N. The electrochemical noise technique was used in order to follow the evolution of both the corrosion current and of the open circuit potential of the system during the wear tests. The pH of the artificial saliva solution was varied between 4 and 7. Results show that the behaviour of the material is strongly influenced by the pH of the solution. In fact, acidification of the solution improves the electrochemical response of the material, in particular the repassivation kinetics after sliding, in all the test conditions used in this work. However, the characteristics of the passive film formed on the material surface appear to be less protective than that formed at neutral pH. Also, an abnormal amount of titanium is removed from the material at low pH, when the normal load applied during the wear test is increased.

The fretting wear of sulphur-deficient MoSx coatings with different crystallographic orientations has been investigated in ambient air of controlled relative humidity. The coefficient of friction and the wear rate of MoSx coatings sliding against corundum depend not only on fretting parameters like contact stress, fretting frequency, and relative humidity, but also strongly on the crystallographic orientation of the coatings. For randomly oriented MoSx coatings, the coefficient of friction and the wear rate increased significantly with increasing relative humidity. In contrast, basal-oriented MoSx coatings were less sensitive to relative humidity. The coefficient of friction of both types of MoSx coatings decreased on sliding against corundum with increasing contact stress and decreasing fretting frequency. A correlation between dissipated energy and wear volume is proposed. This approach allows detection in a simple way of differences in fretting wear resistance between random- and basal-oriented MoSx coatings tested in ambient air of different relative humidity.