Effects of bovine serum albumin and hyaluronic acid on the electrochemical response of a CoCrMo alloy to cathodic and anodic excursions

Nickel-free high-nitrogen austenitic steel outperforms CoCrMo alloy regarding tribocorrosion in simulated inflammatory synovial fluids

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 FeCrMnMoN_0.9 steel (DIN/EN X13CrMnMoN18-14-3, 1.4452), and of the low carbon CoCrMo_0.03 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 CoCrMo_0.03 and FeCrMnMoN_0.9 were comparable in fluids without H₂ O₂ . With higher H₂ O₂ concentrations, tribocorrosion increased for CoCrMo_0.03 , while this was not the case for FeCrMnMoN_0.9 . HA significantly enhanced wear of CoCrMo_0.03 in the absence of H₂ O₂ , while it mitigated the tribocorrosive action of 3 mM H₂ O₂ ; HA had no impact on FeCrMnMoN_0.9 . These results indicate a favorable performance of FeCrMnMoN_0.9 compared to CoCrMo_0.03 , and encourage further research on AHNS for certain orthopedic applications.

Biotribometer for Assessment of Cell and Tissue Toxicity of Orthopedic Metal Implant Debris

A novel approach to address the clinical issue of cell response to wear and corrosion debris from metal orthopedic implants consists of combining cell culturing with wear and corrosion debris generation. A biotribometer equipped with a three-electrode electrochemical chamber operates inside a CO₂ incubator. Cells are cultured at the bottom of the chamber. A ceramic ball (hip implant head) is pressed against a metal disc under a constant load, and set in reciprocating rotation. An anodic electrochemical potential can be applied to a metal disc for accelerated corrosion conditions, or the free potential may be monitored.Measurements of gravimetric and volumetric material loss of the metal disc postwear provide quantitative information that can be put in relation to biological assays (e.g., cell viability and secretion of proinflammatory cytokines). This approach allows for the comparison of candidate metals potentially undergoing tribocorrosion in clinical use. The approach allows to identify the effect of any metastable debris, likely active in vivo.

Fretting-corrosion of CoCr-alloys against TiAl6V4: The importance of molybdenum in oxidative biological environments

Periprosthetic fluids often contain reactive oxygen species, including H₂O₂, 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 H₂O₂. 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 H₂O₂ 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 H₂O₂ 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 ± H₂O₂ (p < .0005). The wear scar was deeper for the Mo-free alloy, and this was significant (p = .013) in the presence of H₂O₂. These findings suggest a marked weakening of the passive film in the presence of H₂O₂, which is mitigated by the availability of Mo.

Corrosion resistance of the nickel-free high-nitrogen steel FeCrMnMoN0.9 under simulated inflammatory conditions

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 "R_P ", 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 R_P 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 R_P 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.

An Overview of Serum Albumin Interactions with Biomedical Alloys

Understanding the interactions between biomedical alloys and body fluids is of importance for the successful and safe performance of implanted devices. Albumin, as the first protein that comes in contact with an implant surface, can determine the biocompatibility of biomedical alloys. The interaction of albumin with biomedical alloys is a complex process influenced by numerous factors. This literature overview aims at presenting the current understanding of the mechanisms of serum albumin (both Bovine Serum Albumin, BSA, and Human Serum Albumin, HSA) interactions with biomedical alloys, considering only those research works that present a mechanistic description of the involved phenomena. Widely used biomedical alloys, such as 316L steel, CoCrMo and Titanium alloys are specifically addressed in this overview. Considering the literature analysis, four albumin-related phenomena can be distinguished: adsorption, reduction, precipitation, and protein-metal binding. The experimental techniques used to understand and quantify those phenomena are described together with the studied parameters influencing them. The crucial effect of the electrochemical potential on those phenomena is highlighted. The effect of the albumin-related phenomena on corrosion behavior of biomedical materials also is discussed.