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The performance of CoCrMo alloy in orthopaedic implants may be unfavourably affected by hyaluronic acid (HA) in synovial fluid. In this study, the authors aimed to understand the interactions between HA and CoCrMo using dedicated electrochemical experiments and surface analyses. A sequence of electrochemical measurements (open‐circuit potential, linear polarization resistance, potentiodynamic and potentiostatic polarizations) was run on LC‐CoCrMo (ASTM F1537) in Dulbecco's phosphate‐buffered saline (DPBS) solution with and without HA and in DPBS mixed with newborn calf serum (NCS) and HA, partially under simultaneous recording of surface pH using custom‐made microelectrodes. Samples were analysed by optical and electron microscopy. HA had no significant impact on the corrosion potential of CoCrMo alloy (ECORR = −173 ± 8, −211 ± 16, and −254 ± 30 mVAg/AgCl, in DPBS, DPBS + HA, and DPBS + NCS + HA, respectively). Average current density values at the transpassive domain were double in DPBS compared to DPBS + HA and DPBS + NCS + HA. At potentials above +0.6 VAg/AgCl, surface pH values decreased from 7.5 to 6.5 in DPBS and from 7.5 to below 4 in DPBS + HA. In conclusion, the presence of HA did not compromise the corrosion resistance of CoCrMo alloy at free potential, but it enhanced acidic conditions at the near surface under anodic‐applied potential in the transpassive domain.

We report on the observation of non-metallic electrical conduction, resistive switching, and a negative temperature coefficient of resistance in cluster-assembled nanostructured gold films above the electrical percolation and in strong-coupling regime, from room to cryogenic temperatures (24K). The structure of the films is characterized by an extremely high density of randomly oriented crystalline nanodomains, separated by grain boundaries. The observed behavior can be explained by considering space charge limited conduction and Coulomb blockade phenomena highlighting the influence of the high density of defects and grain boundaries on the localization of conduction electrons. Our findings have implications for a broad class of resistive switching systems based on random assemblies of nanoobjects., Comment: 12 pages, 4 figures

CoCrMo alloys are well-established biomaterials used for orthopedic joint replacement implants. However, such alloys have been associated with clinical problems related to wear and corrosion. A new generation of austenitic high-nitrogen steels (AHNSs) has been developed for biomedical applications. Here, we have addressed influences of hyaluronic acid, combined with inflammatory (oxidizing) conditions, on tribocorrosion of the high-nitrogen FeCrMnMoN0.9 steel (DIN/EN X13CrMnMoN18-14-3, 1.4452), and of the low carbon CoCrMo0.03 alloy (ISO 5832-12). We aimed to elucidate critical and clinically relevant conditions affecting the implant's performance in certain orthopedic applications. Tribocorrosion tests were conducted in triplicate, with discs under reciprocating sliding wear against a ceramic ball. Different lubricants were prepared from standardized bovine serum solution (ISO 14242-1), with variable additions of hyaluronic acid (HA) and hydrogen peroxide (H2 O2 ). Test conditions were: 37°C, 86,400 cycles, 37 N load (20-40 MPa after run-in phase). Volumetric wear was quantified; surfaces were evaluated by electrochemical parameters and microscopy/spectroscopy analyses (SEM/EDS). Factorial analysis of variance tests was conducted to examine the effects of HA, H2 O2 , and test material on wear- and corrosion-related dependent variables. Tribocorrosion performances of CoCrMo0.03 and FeCrMnMoN0.9 were comparable in fluids without H2 O2 . With higher H2 O2 concentrations, tribocorrosion increased for CoCrMo0.03 , while this was not the case for FeCrMnMoN0.9 . HA significantly enhanced wear of CoCrMo0.03 in the absence of H2 O2 , while it mitigated the tribocorrosive action of 3 mM H2 O2 ; HA had no impact on FeCrMnMoN0.9 . These results indicate a favorable performance of FeCrMnMoN0.9 compared to CoCrMo0.03 , and encourage further research on AHNS for certain orthopedic applications.

Periprosthetic fluids often contain reactive oxygen species, including H(2)O(2), that are generated during inflammatory processes. Here, we investigated the fretting-corrosion behavior of CoCrX-alloys (X = Mo, Fe) in a complex protein-containing lubricant, with and without the addition of H(2)O(2). Given the known protective role of molybdenum as an alloying element in metal degradation, we considered its effects by designing a two-way factorial experiment. The aim of the study was to investigate tribocorrosive mechanisms in modular joints of knee and hip prostheses. A previously described test-rig was used to run fretting corrosion tests of CoCrX-alloys with (X=Mo) and without (X=Fe) molybdenum against TiAl6V4 in bovine calf serum (BCS) with and without a physiological relevant H(2)O(2) level (3 mM) in gross slip mode (4 Hz, ±50 μm, p(max)=0.18 GPa, 37 °C, 50,000 cycles). Two CoCr-pins were pressed against a cylindrical TiAl6V4-rod, forming a line contact. Normal and frictional forces, the displacement, and the open circuit potential (OCP) were measured and recorded continuously. The dissipated frictional work was independent of alloy composition. The addition of H(2)O(2) lowered the dissipated frictional work and increased wear, and this was significant in the absence of Mo. The mean OCP value was lower with Mo-containing than with Mo-free alloy in both pure BCS (p = .042), and BCS ± H(2)O(2) (p < .0005). The wear scar was deeper for the Mo-free alloy, and this was significant (p = .013) in the presence of H(2)O(2). These findings suggest a marked weakening of the passive film in the presence of H(2)O(2), which is mitigated by the availability of Mo.

Nickel-free, high-nitrogen austenitic steels (AHNS) have been introduced for biomedical applications, with encouraging results in terms of mechanical and corrosion properties. Here, we tested the corrosion resistance of a nickel-free high nitrogen steel (FeCrMnMoN0.9) in bovine serum solutions containing 0 or 3 g/L hyaluronic acid (HA), and 0, 3, or 30 mM hydrogen peroxide (H2 O2 ) simulating no, moderate, or strong inflammatory conditions, respectively. Nondestructive electrochemical measurements (open circuit potential [OCP], linear polarization resistance "RP ", and electrochemical impedance spectroscopy) were run in triplicate over 10 hr. The presence of HA had no significant effect either on the stabilized OCP values, or on the corrosion resistance of FeCrMnMoN0.9. Increasing H2 O2 concentrations shifted the OCP to more electropositive values; the corrosion resistance decreased only at a 30 mM H2 O2 . Final RP values at 0, 3, and 30 mM H2 O2 resulted in 1598 ± 276, 1746 ± 308, and 439 ± 47 kΩ cm2 , respectively. These values were 4-14 times higher, than the RP values measured on LC-CoCrMo in our previous study, conducted under identical conditions. While these findings are encouraging, future studies need to focus on tribocorrosive properties of the AHNS to evaluate its applicability in joint replacement.

During joint inflammation, various reactive oxygen species (ROS) are present in the surrounding tissue and joint fluid. In the laboratory, hydrogen peroxide (H(2)O(2)) is typically used to simulate inflammatory conditions, and media containing proteins and hyaluronic acid (HA) are employed to simulate joint synovial fluid. Electrochemical interactions between H(2)O(2) and HA in the presence of a CoCrMo surface are expected, since HA molecules contain redox-active moieties. We hypothesized that any redox reactions of these moieties with ROS will mitigate the oxidizing effect of H(2)O(2) on the CoCrMo surface, limiting the corrosion rate of the metal. Non-destructive electrochemical measurements (open circuit potential, linear polarization resistance and electrochemical impedance spectroscopy) were used to investigate the corrosion response of CoCrMo in synovial model fluid containing physiologically relevant concentrations of albumin proteins and hyaluronic acid, with and without H(2)O(2). Two different molarities of H(2)O(2), 3 mM and 30 mM, were tested. While both molarities are within physiological limits, 3mM is well within the range HA could mitigate, whereas 30 mM is not. Contrary to our hypothesis, HA did not alleviate corrosion in 3 mM H(2)O(2) and even caused a corrosion increase in the case of 30 mM H(2)O(2). The decrease in corrosion resistance of the alloy may be attributed to the complexation of degenerated HA molecular chains with chromium ions released from the metallic surface, which are necessary to build a protective oxide film. This finding has clinical implications, suggesting that HA accelerates corrosion of CoCrMo implants in the presence of strong inflammation.

Wear and corrosion in total hip replacement negatively impact implant service-life and patient well-being. The aim of this study was to generate a statistical response surface of material loss using an apparatus, capable of testing the effect of wear and corrosion products in situ on cells, such as macrophages. The test chamber of a ball-on-flat tribometer operating inside a CO2 incubator was integrated with an electrochemical setup and adapted for cell culture work. A 20-test series, following a 2-level 3-factor design of experiments, was performed with a ceramic head in reciprocating rotational motion against a CoCrMo-alloy disc, under constant load. The lubricant was cell culture medium (RPMI-1640 + 10 vol% bovine serum). Response surfaces were generated, which statistically showed the influence of motion amplitude, load, and potential on the total mass loss and wear scar volume of the metallic discs. Potential had the highest impact on the total mass loss, while motion amplitude and load significantly influenced the wear scar volume. The concentrations of the alloy elements found in the lubricants reflected the bulk-alloy stoichiometry. The total concentration of Co released into the lubricant (2.3–63 ppm by total mass loss, 1.5 to 62 ppm by ICP-MS) corresponded well with the known range to trigger cell response. Tribocorrosion tests in the presence of cells and tissues, such as macrophages, lymphocytes and/or synovium, will be carried out in the future.

Tribocorrosion of implants has been widely addressed in the orthopedic and dental research fields. This study is a systematic scoping review about research methods that combine tribocorrosion tests with cells/tissues cultures, aimed to identify related current problems and future challenges. We used 4 different databases to identify 1022 records responding to an articulated keywords search-strategy. After removing the duplicates and the articles that didn't meet the search-criteria, we assessed 20 full-text articles for eligibility. Of the 20 eligible articles, we charted 8 records on cell cultures combined with tribocorrosion tests on implant materials (titanium, CoCrMo, and/or stainless steel). The year of publication ranged from 1991 to 2019. The cell line used was mostly murine. Two records used fretting tests, while 6 used reciprocating sliding with pin-on-disc tribometers. An electrochemical three-electrode setup was used in 4 records. We identified overall two experimental approaches: cells cultured on the metal (5 records), and cells cultured near the metal (3 records). Research activities on tribocorrosion processes in the presence of cells have been undertaken worldwide by a few groups. After a limited initial interest on this topic in the 1990's, research activities have restarted in the last decade, renewing the topic with technologically more advanced setups and analytical tools. We identified the main problems to be the lack of test reproducibility and wear particle characterization. We believe that the main challenges lay in the interdisciplinary approach, the inter-laboratory validation of experiments, and the interpretation of results, particularly in relation to potential clinical significance.

Titanium is an interesting material for biomedical implants thanks to its physical and chemical properties. In particular, TiO2 coatings with a surface characterized by micro-patterning combined with nano-topography are extremely attractive for orthopaedic implants in terms of enhanced osteointegration and consequently improved implant fixation. In the present work, a new method for the preparation of TiO2 multi-scale structured coatings is presented. This method is based on three steps. Firstly, monodispersed polystyrene (PS) microsized beads are functionalized with TiO2 submicron particles by a wet process involving a cationic polyelectrolyte. Secondly, the resulting TiO2-PS composite particles in suspension are used to prepare coatings by electrophoretic deposition (EPD), a simple and flexible electrochemical technique. The EPD is performed cathodically, avoiding uncontrolled oxidation of the substrate. Finally, after removal of the PS spacers during the sintering process, TiO2 coatings with a combined micro- and nano-topography are achieved from deposits thicker than 100 mu m. This achievement presents two relevant aspects: potential applications of the multi-scale structured TiO2 surfaces (particularly in the biomedical field); the simplicity and flexibility of the process used. (C) 2009 Elsevier B.V. All rights reserved.

Composite bilayer coatings on Ti6Al4V substrates were prepared by electrophoretic deposition, a simple and fast low temperature coating technique. Biocompatible yttrium-stabilized zirconia (YSZ) in the form of nanoparticles and bioactive Bioglass® (45S5) in the form of microparticles were chosen as coating materials. The first layer consisted of 5 μm of YSZ, deposited with the intention to avoid any metal tissue contact. The second layer consisted of 15-μm thick 45S5-YSZ composite, supposed to react with the surrounding bone tissue and to enhance implant fixation. The adsorption of YSZ nanoparticles on 45S5 microparticles in organic suspension was found to invert the surface charge of the 45S5 particles from negative to positive. This enabled cathodic electrophoretic deposition of 45S5, avoiding uncontrolled anodization (oxidation) of the substrate. The coatings were sintered at 900°C for 2 h under argon flow. The characterization was performed using SEM, EDX, and nanoindentation (cross section). Potential applications in the orthopedics field are discussed. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007

The effect of alumina nanoparticles suspended in an aqueous acetate buffer solution on the tribocorrosion behaviour of a 316L steel/alumina sliding contact was investigated using a reciprocating wear test rig equipped with an electrochemical cell. Through the addition of 10% volume of alumina nanoparticles to an acetate buffer solution it was possible to reduce the coefficient of friction by a factor of 2 and the stainless steel wear by a factor of 10 and this over a range of electrochemical and mechanical conditions. The presence of alumina particles caused a significant wear on the alumina counter part. The lubricating behaviour of the suspension was comparable to a commercial oil in water emulsion used for metal cutting. The lubricating effect was attributed to a third body formed by nanoparticles trapped within the contact. The agglomeration state of the alumina particles and their size were found to play a critical role.

In this work a new class of ionomeric block perfluropolyether (PFPE) polyurethanes are presented; these polymers are obtained in the form of aqueous dispersions due to the presence of hydrophilic sites (ionomeric groups such as acetates or trialkylammonium salts) along the macromolecular chain, offering the chance to combine PFPEs in a variety of possible structures for coating or surface treatments with an environmentally friendly use. X-ray photoelectron spectroscopy analysis at two different sampling depths, as well as time-of-flight secondary ion mass spectrometry analysis modelled by the use of principal component analysis (PCA), were used to investigate the first nanometres of the surface samples. It resulted in a clear surface enrichment in fluorine, and the different extent of the fluorine stratification will be discussed in relation to the ionic character, film-forming from water and cross-linking. Copyright © 2003 John Wiley & Sons, Ltd.

A surface study of two different monocomponent polyurethane coatings containing perfluoropolyether macromers is presented. Different techniques were used in order to investigate the structural characteristics of the two polymers. In particular, transmission infrared spectroscopy provided information about the chemical groups and linkages present in the polymer network, and attenuated total reflectance spectra showed a higher concentration of urea groups close to the surface. X-ray photoelectron spectroscopy analysis at two different sampling depths showed clear evidence of fluorine enrichment and nitrogen depletion in the first nanometres of material with respect to the bulk composition of the two polymers. Analysis of the outermost layer by time-of-flight secondary ion mass spectrometry confirmed the XPS data with a predominant presence of fluorinated fragments. Contact angles of the two coatings with water and paraffins were measured and the critical surface tension of wetting, γc, was estimated (13–16 mN m−1 at 20 °C) and compared with the known data of other fluoropolymers. Copyright © 2000 John Wiley & Sons, Ltd.

In this work, a high molecular weight copolymer of tetrafluoroethylene and perfluoro-4-trifluoromethoxy-1,3-dioxole (HYFLON® AD60) and two perfluoropolyethers (PFPEs) containing ammonium phosphate or triethoxysilane functionalities, FLUOROLINK® F10 and FLUOROLINK® S10 respectively, have been evaluated as protective coatings that can be easily applied on anodized titanium surfaces. Water and n-dodecane contact angle measurements have been recorded by using the sessile drop method for bare and coated surfaces in order to determine the hydrophobic and oleophobic properties of the coatings. The UV-stability of coatings have been studied by Fourier transform infrared spectroscopy (FT-IR) analyses and by observing the variation of water contact angles on coated substrates before and after UV irradiation at regular time intervals. The thickness of the fluorinated films has been measured by ellipsometry and by weight evaluation. Preliminary tests of the adhesion between films and substrate have been conducted.

Functionalization of colloidal particles based on the use of polyelectrolytes and heterocoagulation was combined with electrophoretic deposition (EPD), with the aim of depositing titania-polystyrene (TiO2-PS) composite particles on Ti6A14V substrates. The composite particles were obtained by heterocoagulation of TiO2 nanoparticles on the surface of monosized polystyrene beads of 4.6 mu m in diameter. Two alternative methods were developed for the preparation of the TiO2-PS suspensions in organic fluids for cathodic electrodeposition. The first method was carried out in alkaline aqueous medium with the use of polyelectrolytes and intermediate control measurements of zeta potential, conductivity, and pH; the second one was carried out directly in the organic solvent used for EPD, typically isopropanol. Examples of deposits obtained by EPD in both suspensions and a comparative analysis between the two methods are presented. (c) 2007 Elsevier Inc. All rights reserved.

The behaviour of suspended AI 2 O 3 nanoparticles in a tribocorrosion system was experimentally investigated. The test configuration involved an alumina ball rubbing against a stainless steel plate in a reciprocating motion wear test rig. The contact was immersed in an acetate buffer solution with or without nanoparticles. The stainless steel plate was kept under controlled potential and the anodic current was measured using a three-electrode electrochemical set up. The evolution of friction and wear (vertical contact displacement) during rubbing were continuously measured. The presence A1 2 O 3 nanoparticles lowered significantly the extent of metallic wear and reduced friction. The observed close correlation among the variations of current, friction and vertical displacement indicates that the nanoparticles act as lubricant by forming a third body protecting the metal.

A new stabilizer for fluorinated lubricants, either oils or greases, was developed stemming from the chemistry of perfluoropolyethers. The additive shows good efficiency in improving the stability of perfluoropolyether oils at very high temperatures in presence of metals and under oxidative environments, extending thus the life of the formulated lubricants. Some specific tests were carried out in order to assess performances in applications. Furthermore, as a first approach, grazing infrared reflection-absorption spectroscopy was used as a probe for studying structural and topological issues relative to additive-surface interactions.Copyright © 2005 by ASME

The role of particle concentration in electrophoretic deposition (EPD) was investigated with two different suspension systems. The first system consisted of positively charged TiO2 nanoparticles dispersed in isopropanol with 1 vol% water. The second system consisted of negatively charged polystyrene (PS) microbeads dispersed in isopropanol. Constant voltage EPD was performed using suspensions with variable particle concentration (0.013-0.43 vol% TiO2 and 0.06-11.4 vol% PS). Threshold concentration values were identified for both systems after EPD at 100 V(250 V cm(-1)) for 1 min. Below these values the deposited mass deviated from the trend dictated by Hamaker's equation. Higher applied voltages and longer deposition times were tested and the results suggested that the threshold concentration did not depend on those parameters. A phenomenological model of particle deposition was proposed, which accounts for the local electrochemical conditions close to the substrate in relation to particle size. (C) 2009 Elsevier Ltd. All rights reserved.