The Electrochemical Behavior of Ti in Human Synovial Fluids.

In this study, we report results of the interaction of titanium (Ti) with human synovial fluids. A wide palette of electrochemical techniques was used, including open circuit potential, potentiodynamic methods, and electrochemical impedance. After the electrochemical testing, selected surfaces were analyzed using Auger Electron Spectroscopy to provide laterally resolved information on surface chemistry. For comparison purposes, similar tests were conducted in a series of simulated body fluids. This study shows that compared to the tested simulated body fluids, synovial liquids show a large patient variability up to one order of magnitude for some crucial electrochemical parameters such as corrosion current density. The electrochemical behavior of Ti exposed to human synovial fluids seems to be controlled by the interaction with organic molecules rather than with reactive oxygen species.

Tribocorrosion behaviour of pure titanium in bovine serum albumin solution: A multiscale study.

Tribocorrosion behaviour of pure titanium in phosphate buffer saline (PBS) solution has been investigated systematically as a function of surface chemistry and bovine serum albumin (BSA) content in the solution. A ball-on-disk tribometer coupled with an electrochemical cell was used to study the effect of electrochemical conditions (i.e. anodic and cathodic applied potentials, as well as at open circuit potential) on the tribocorrosion response of titanium. It was found that the main material loss is due to mechanical wear caused by plastic deformation. The mechanical wear was higher under anodic conditions than under cathodic, partially due to an increased presence of debris particles at the sliding interface that act as third bodies. The effect of BSA on the interaction between alumina and titanium, as well as the behaviour of third bodies during the mechanical wear, were investigated in the nanoscale level using atomic force microscopy based force spectroscopy. It was found that the presence of BSA affects tribocorrosion in various ways. Firstly, it increases the repassivation rate of the oxide film by inhibiting the cathodic reactions and accelerating the anodic reactions. Secondly, it increases the mechanical wear by increasing the adhesion of debris onto the sliding interface, while at anodic conditions it increases the rolling efficiency of the debris particles that further enhances the mechanical wear.

Effect of the electrochemical characteristics of titanium on the adsorption kinetics of albumin.

An electrochemical quartz crystal microbalance (EQCM) was used to examine the electrochemical behaviour of pure titanium in phosphate buffered saline (PBS) and PBS-containing bovine serum albumin (BSA) solutions, and the associated adsorption characteristics of BSA under cathodic and anodic applied potentials. It was found that the electrochemical behaviours of bulk titanium substrate and titanium-coated QCM sensors are slightly different in PBS buffer solution, which is attributed to the difference in their surface roughness. The oxide film formed on the surface of the QCM sensor during potentiostatic tests was found to affect its electrochemical behaviour, while cathodic cleaning is not sufficient to have it removed. Lastly, the excessive amount of electrons on the titanium surface upon application of a cathodic potential could result in the desorption of BSA due to electrostatic repulsion and protein dehydration. In contrast, application of anodic potential charges the titanium surface positively and can facilitate protein adsorption when the surface is not saturated with protein.

Electrochemical Behaviour and Galvanic Effects of Titanium Implants Coupled to Metallic Suprastructures in Artificial Saliva.

The aim of the present study is to analyze the electrochemical behavior of five different dental alloys: two cobalt-chromium alloys (CoCr and CoCr-c), one nickel-chromium-titanium alloy (NiCrTi), one gold-palladium alloy (Au), and one titanium alloy (Ti6Al4V), and the galvanic effect when they are coupled to titanium implants (TiG2). It was carried out by electrochemical techniques (open circuit measurements, potentiodynamic curves and Zero-Resistance Ammetry) in artificial saliva (AS), with and without fluorides in different acidic conditions. The studied alloys are spontaneously passivated, but NiCrTi alloy has a very narrow passive domain and losses its passivity in presence of fluorides, so is not considered as a good option for implant superstructures. Variations of pH from 6.5 to 3 in artificial saliva do not change the electrochemical behavior of Ti, Ti6Al4V, and CoCr alloys, and couples, but when the pH of the artificial saliva is below 3.5 and the fluoride content is 1000 ppm Ti and Ti6Al4V starts actively dissolving, and CoCr-c superstructures coupled to Ti show acceleration of corrosion due to galvanic effects. Thus, NiCrTi is not recommended for implant superstructures because of risk of Ni ion release to the body, and fluorides should be avoided in acidic media because Ti, Ti6Al4V, and CoCr-c superstructures show galvanic corrosion. The best combinations are Ti/Ti6Al4V and Ti/CoCr as alternative of noble gold alloys.

Degradation mechanisms and future challenges of titanium and its alloys for dental implant applications in oral environment.

OBJECTIVE: For many decades the failure of titanium implants due to corrosion and wear were approached individually and their synergic effect was not considered. In recent past, developments and understanding of the tribocorrosion aspects have thrown deeper understanding on the failure of implants and this has been reviewed in this article extensively. METHODS: Medline, google scholar and Embase search was conducted to identify studies published between 1993 and 2016 which were related to the analysis of degradation mechanism which the dental implants undergo after implantation. RESULTS: In-vitro tests has been extensively carried out to evaluate the tribocorrosion behavior of titanium based dental implants. However, there is still a lack of knowledge about the tangible behavior of materials under in-vivo condition, because the in-vitro experiments are conducted using different testing protocols and conditions (solutions, pH, time, equipment, and testing parameters). Hence, there is an urgent need to perform round-robin test in different laboratories which will help to overcome the gap between in-vitro and in-vivo conditions. CONCLUSION: Tribocorrosion has been identified as the major degradation mechanisms that result in the failure of dental implants. Hence, it is of utmost importance to improve the service period of dental implants by reducing the tribocorrosion effects through developing new dental implant materials using nobler alloying elements or through modifying the surface of the implants. In order to have a thorough understanding of tribocorrosion behavior and failure mechanisms, round robin test are to be conducted and new protocols/standards are to be developed for the testing of implants.

Influence of the sliding velocity and the applied potential on the corrosion and wear behavior of HC CoCrMo biomedical alloy in simulated body fluids.

The corrosion and tribocorrosion behavior of an as-cast high carbon CoCrMo alloy immersed in phosphate buffered solution (PBS) and phosphate buffered solution with bovine serum albumin (PBS+BSA) have been analyzed by electrochemical techniques and surface microscopy. After the electrochemical characterization of the alloy in both solutions, the sample was studied tribo-electrochemically (by open circuit potential, OCP measurements, potentiodynamic curves and potentiostatic tests) in a ball-on-disk tribometer rotating in different sliding velocities. The influence of solution chemistry, sliding velocity and applied potential on the corrosion and tribocorrosion behavior of the CoCrMo alloy has been studied. Anodic current density increases with sliding velocity but wear rate does not change at an applied anodic potential; on the other hand, BSA modifies the wear debris behavior (by agglomerating the debris formed by mechanical removal of particles) thus increasing the mechanical wear volume. Under cathodic conditions, cathodic current density also increases during mechanical contact while the wear rate decreases with sliding velocity and BSA lubricates the contact thus reducing the total wear volume with respect to the non-containing BSA solution. The work shows how the electrode potential critically affects the corrosion and tribocorrosion rates by increasing the wear coefficients at applied anodic potentials due to severe wear accelerated corrosion.