Tribocorrosion Mechanisms of Ti6Al4V in Artificial Saliva by Zero-Resistance Ammetry (ZRA) Technique

[EN] Degradation mechanisms of biomedical alloys involve two different phenomena, corrosion and wear, which simultaneously act and may cause the failure of implants and prosthesis. In this work, tribocorrosion of Ti6Al4V biomedical alloy in artificial saliva is studied at open circuit potential (OCP) by a new electrochemical technique that allows measuring the galvanic potential and current between the wear track (anode) and the passive material (cathode) through zero-resistance ammetry. The experimental set-up was conceived for physically separating the depassivated area from the passive material, thus allowing to quantify the mechanically activated corrosion at OCP. Two different counterparts, SiC and Al2O3, were used against the Ti6Al4V alloy in order to analyse the influence of the initial contact pressure on the tribocorrosion mechanisms. A galvanic model based on the cathodic reaction kinetics can describe the current and the potential evolution with time during sliding. It has been observed that at the highest initial contact pressures, wear follows the Archard law, while at lower contact pressures, third body appeared and wear can not be described by the Archard law. Quantification of the evolution of the depassivated wear track with time was obtained and the deviation from the Archard predictions was analysed.The authors would like to thank the financial support from NTNU (Project Number 69450741) for performing the experiments of this work and Universitat Politècnica de Valencia VLC/Campus (PMIA-2013) for the mobility Grant.Licausi, M.; Igual Muñoz, AN.; Amigó, V.; Espallargas, N. (2015). Tribocorrosion Mechanisms of Ti6Al4V in Artificial Saliva by Zero-Resistance Ammetry (ZRA) Technique. Journal of Bio- and Tribo-Corrosion (Online). 1(8):1-11. https://doi.org/10.1007/s40735-015-0008-xS11118Martin É, Azzi M, Salishchev GA, Szpunar J (2010) Influence of microstructure and texture on the corrosion and tribocorrosion behaviour of Ti–6Al–4V. Tribol Int 43:918–924Nosonovsky M, Bhushan B (2010) Green tribology: principles, research areas and challenges. Philos Trans R Soc A 368:4677–4694Geetha M, Singh AK, Asokamani R, Gogia AK (2009) Ti based biomaterials, the ultimate choice for orthopaedic implants—a review. Prog Mater Sci 54:397–425Niinomi M, Kuroda D, Fukunaga K, Morinaga M, Kato Y, Yashiro T et al (1999) Corrosion wear fracture of new β type biomedical titanium alloys. Mater Sci Eng A 263:193–199Kuroda D, Niinomi M, Morinaga M, Kato Y, Yashiro T (1998) Design and mechanical properties of new β type titanium alloys for implant materials. Mater Sci Eng A 243:244–249Eisenbarth E, Velten D, Müller M, Thull R, Breme J (2004) Biocompatibility of β-stabilizing elements of titanium alloys. Biomaterials 25:5705–5713More NS, Diomidis N, Paul SN, Roy M, Mischler S (2011) Tribocorrosion behaviour of β titanium alloys in physiological solutions containing synovial components. Mater Sci Eng C 31:400–408Milošev I, Metikoš-Huković M, Strehblow H-H (2000) Passive film on orthopaedic TiAlV alloy formed in physiological solution investigated by X-ray photoelectron spectroscopy. Biomaterials 21:2103–2113Komotori J, Hisamori N, Ohmori Y (2007) The corrosion/wear mechanisms of Ti–6Al–4V alloy for different scratching rates. Wear 263:412–418Dimah MK, Devesa Albeza F, Amigó Borrás V, Igual Muñoz A (2012) Study of the biotribocorrosion behaviour of titanium biomedical alloys in simulated body fluids by electrochemical techniques. Wear 294–295:409–418Licausi MP, Igual Muñoz A, Amigó Borrás V (2013) Tribocorrosion mechanisms of Ti6Al4V biomedical alloys in artificial saliva with different pHs. J Phys D 46:404003Runa MJ, Mathew MT, Rocha LA (2013) Tribocorrosion response of the Ti6Al4V alloys commonly used in femoral stems. Tribol Int 68:85–93Munoz AI, Espallargas N (2011) Tribocorrosion mechanisms in sliding contacts. In: Landolt D, Mischler S (eds) Tribocorrosion of passive metals and coatings. Woodhead Publishing, LausanneMischler S (2008) Triboelectrochemical techniques and interpretation methods in tribocorrosion: a comparative evaluation. Tribol Int 41:573–583Espallargas N, Johnsen R, Torres C, Muñoz AI (2013) A new experimental technique for quantifying the galvanic coupling effects on stainless steel during tribocorrosion under equilibrium conditions. Wear 307:190–197Vieira AC, Rocha LA, Papageorgiou N, Mischler S (2012) Mechanical and electrochemical deterioration mechanisms in the tribocorrosion of Al alloys in NaCl and in NaNO3 solutions. Corros Sci 54:26–35Papageorgiou N, Mischler S (2012) Electrochemical simulation of the current and potential response in sliding tribocorrosion. Tribol Lett 48(3):271–283Papageorgiou N, von Bonin A, Espallargas N (2014) Tribocorrosion mechanisms of NiCrMo-625 alloy: an electrochemical modeling approach. Tribol Int 73:177–186Dearnley PA, Dahm KL, Çimenoglu H (2004) The corrosion-wear behaviour of thermally oxidised CP-Ti and Ti-6Al-4V. Wear 256:469–47

Tribocorrosion of Pulsed Plasma-Nitrided CoCrMo Implant Alloy

In the present study, a forged CoCrMo (ISO 5832-12) has been subjected to pulsed plasma treatment in a N-2/H-2 atmosphere at low temperatures (below 500 A degrees C). This treatment resulted in the formation of a layer composed by dispersed chromium nitride particles in a N-enriched metal matrix. The materials were tested for corrosion and tribocorrosion performance in 0.9 wt% NaCl at room temperature under controlled electrochemical conditions. After the treatment, the alloy loses its passive nature. The electrode potential was found to critically affect the corrosion and the tribocorrosion rates. In the nitrided alloy, a significant increase of corrosion rate was found at high potentials, while tribocorrosion was determined mainly by mechanical wear and not affected by potential. On the other hand, the untreated CoCrMo alloy exhibited stable corrosion over a wide range of potentials. Its tribocorrosion rate was similar to the nitrided alloy samples at low potentials, but it increased dramatically at high potentials where passivity triggered severe wear-accelerated corrosion and promoted mechanical wear. The present study shows that the electrochemical conditions determine material deterioration and should therefore be considered when selecting materials for tribocorrosion applications such as biomedical implants

Modeling the effects of concentration of solid nanoparticles in liquid feedstock injection on high-velocity suspension flame spray process

This paper presents the effects of the concentration of solid nanoparticles in the liquid feedstock injection on the high-velocity suspension flame spray (HVSFS) process. Four different concentrations of solid nanoparticles in suspension droplets with various droplet diameters are used to study gas dynamics, vaporization rate, and secondary breakup. Two types of injections, viz. surface and group, are used. The group-type injection increases the efficiency of droplet disintegration and the evaporation process and reduces the gas cooling. The initiation of the fragmentation process is difficult for small droplets carrying a high concentration of nanoparticles. Also, smaller droplets undergo rapid vaporization, leaving clogs of nanoparticles in the middle of the barrel. For larger droplets, severe fragmentation occurs inside the combustion chamber. For a higher concentration of nanoparticles, droplets exit the gun without complete evaporation. The results suggest that, in coating applications involving a higher concentration of nanoparticles, smaller droplet sizes are preferred

A new experimental technique for quantifying the galvanic coupling effects on stainless steel during tribocorrosion under equilibrium conditions

Galvanic coupling during tribocorrosion of passive metals at open circuit potential (OCP) generates a wear-accelerated corrosion process within the depassivated area (worn surface) that is electrically in contact with the still passive one. The galvanic coupling effect at OCP was recently modeled using an electrochemical approach allowing for the theoretical quantification of the wear-accelerated corrosion under equilibrium conditions. Despite the usefulness of this model that mathematically determines the electrochemical conditions inside the wear track in terms of anode potential via the approximation of the net anodic current density, an experimental technique allowing for their experimental determination is essential in the effort to verify the galvanic coupling models and further understand the tribocorrosion mechanisms at OCP. In the present work, a new experimental technique based on galvanic current and potential measurements through a Zero-Resistance Ammeter (ZRA) for quantifying the electrode potential and anodic current inside the wear track during rubbing at OCP has been assessed. This experimental set-up has allowed for the first time to determine the prevailing electrochemical conditions (electrode potential and anodic current) inside the wear track by solely exposing the wear track to the electrolyte and physically separating the cathode from the anode (wear track). The effects of sliding wear at open circuit potential have been investigated for a super duplex stainless steel (UNS S32750) in 3.4 wt% NaCl. The new experimental set-up proposed in this work separates the cathode from the anode and exposes solely the wear track to the electrolyte. Using well-established electrochemical theories, the effect of the extent of the galvanic coupling on wear at the open circuit potential conditions has been quantified.The authors would like to thank the support from the European Union for funding C. Torres through the Leonardo da Vinci Mobility program. C.B. von der Ohe and E. Jensen are also acknowledged for having taken part in the initial phase 1151 of this long project. Dr. N. Papageorgiou (NTNU) is also acknowledged for the input and calculations in the modeling part and for preparing Figs. 6-9 of the paper.Espallargas Álvarez, N.; Johnsen, R.; Torres, C.; Igual Muñoz, AN. (2013). A new experimental technique for quantifying the galvanic coupling effects on stainless steel during tribocorrosion under equilibrium conditions. Wear. 307(1-2):190-197. doi:10.1016/j.wear.2013.08.026S1901973071-

Bovine Serum Albumin binding to CoCrMo nanoparticles and the influence on dissolution

CoCrMo alloys exhibit good mechanical properties, excellent biocompatibility and are widely utilised in orthopaedic joint replacements. Metal-on-metal hip implant degradation leads to the release of metal ions and nanoparticles, which persist through the implant's life and could be a possible cause of health complications. This study correlates preferential binding between proteins and metal alloy nanoparticles to the alloy's corrosion behaviour and the release of metal ions. TEM images show the formation of a protein corona in all particles immersed in albumin containing solutions. Only molybdenum release was significant in these tests, suggesting high dissolution of this element when CoCrMo alloy nanoparticles are produced as wear debris in the presence of serum albumin. The same trend was observed during extended exposure of molybdenum reference nanoparticles to albumin

Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively

Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization

Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust, and magnetic functionalized monolayers of coordination polymers. A series of five isoreticular layered magnetic coordination polymers based on Fe(II) centres and different benzimidazole derivatives (bearing a Cl, H, CH3, Br or NH2 side group) were first prepared. On mechanical exfoliation, 2D materials are obtained that retain their long-range structural order and exhibit good mechanical and magnetic properties. This combination, together with the possibility to functionalize their surface at will, makes them good candidates to explore magnetism in the 2D limit and to fabricate mechanical resonators for selective gas sensing

Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).

Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)

Improved risk stratification of patients with atrial fibrillation: an integrated GARFIELD-AF tool for the prediction of mortality, stroke and bleed in patients with and without anticoagulation.

OBJECTIVES: To provide an accurate, web-based tool for stratifying patients with atrial fibrillation to facilitate decisions on the potential benefits/risks of anticoagulation, based on mortality, stroke and bleeding risks. DESIGN: The new tool was developed, using stepwise regression, for all and then applied to lower risk patients. C-statistics were compared with CHA2DS2-VASc using 30-fold cross-validation to control for overfitting. External validation was undertaken in an independent dataset, Outcome Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF). PARTICIPANTS: Data from 39 898 patients enrolled in the prospective GARFIELD-AF registry provided the basis for deriving and validating an integrated risk tool to predict stroke risk, mortality and bleeding risk. RESULTS: The discriminatory value of the GARFIELD-AF risk model was superior to CHA2DS2-VASc for patients with or without anticoagulation. C-statistics (95% CI) for all-cause mortality, ischaemic stroke/systemic embolism and haemorrhagic stroke/major bleeding (treated patients) were: 0.77 (0.76 to 0.78), 0.69 (0.67 to 0.71) and 0.66 (0.62 to 0.69), respectively, for the GARFIELD-AF risk models, and 0.66 (0.64-0.67), 0.64 (0.61-0.66) and 0.64 (0.61-0.68), respectively, for CHA2DS2-VASc (or HAS-BLED for bleeding). In very low to low risk patients (CHA2DS2-VASc 0 or 1 (men) and 1 or 2 (women)), the CHA2DS2-VASc and HAS-BLED (for bleeding) scores offered weak discriminatory value for mortality, stroke/systemic embolism and major bleeding. C-statistics for the GARFIELD-AF risk tool were 0.69 (0.64 to 0.75), 0.65 (0.56 to 0.73) and 0.60 (0.47 to 0.73) for each end point, respectively, versus 0.50 (0.45 to 0.55), 0.59 (0.50 to 0.67) and 0.55 (0.53 to 0.56) for CHA2DS2-VASc (or HAS-BLED for bleeding). Upon validation in the ORBIT-AF population, C-statistics showed that the GARFIELD-AF risk tool was effective for predicting 1-year all-cause mortality using the full and simplified model for all-cause mortality: C-statistics 0.75 (0.73 to 0.77) and 0.75 (0.73 to 0.77), respectively, and for predicting for any stroke or systemic embolism over 1 year, C-statistics 0.68 (0.62 to 0.74). CONCLUSIONS: Performance of the GARFIELD-AF risk tool was superior to CHA2DS2-VASc in predicting stroke and mortality and superior to HAS-BLED for bleeding, overall and in lower risk patients. The GARFIELD-AF tool has the potential for incorporation in routine electronic systems, and for the first time, permits simultaneous evaluation of ischaemic stroke, mortality and bleeding risks. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier for GARFIELD-AF (NCT01090362) and for ORBIT-AF (NCT01165710)

Two-year outcomes of patients with newly diagnosed atrial fibrillation: results from GARFIELD-AF.

AIMS: The relationship between outcomes and time after diagnosis for patients with non-valvular atrial fibrillation (NVAF) is poorly defined, especially beyond the first year. METHODS AND RESULTS: GARFIELD-AF is an ongoing, global observational study of adults with newly diagnosed NVAF. Two-year outcomes of 17 162 patients prospectively enrolled in GARFIELD-AF were analysed in light of baseline characteristics, risk profiles for stroke/systemic embolism (SE), and antithrombotic therapy. The mean (standard deviation) age was 69.8 (11.4) years, 43.8% were women, and the mean CHA2DS2-VASc score was 3.3 (1.6); 60.8% of patients were prescribed anticoagulant therapy with/without antiplatelet (AP) therapy, 27.4% AP monotherapy, and 11.8% no antithrombotic therapy. At 2-year follow-up, all-cause mortality, stroke/SE, and major bleeding had occurred at a rate (95% confidence interval) of 3.83 (3.62; 4.05), 1.25 (1.13; 1.38), and 0.70 (0.62; 0.81) per 100 person-years, respectively. Rates for all three major events were highest during the first 4 months. Congestive heart failure, acute coronary syndromes, sudden/unwitnessed death, malignancy, respiratory failure, and infection/sepsis accounted for 65% of all known causes of death and strokes for <10%. Anticoagulant treatment was associated with a 35% lower risk of death. CONCLUSION: The most frequent of the three major outcome measures was death, whose most common causes are not known to be significantly influenced by anticoagulation. This suggests that a more comprehensive approach to the management of NVAF may be needed to improve outcome. This could include, in addition to anticoagulation, interventions targeting modifiable, cause-specific risk factors for death. CLINICAL TRIAL REGISTRATION: http://www.clinicaltrials.gov. Unique identifier: NCT01090362