Effects of simulated inflammation on the corrosion of 316L stainless steel

The Mechanical and Electrochemical Stability of Trimethysilane Plasma Nanocoatings Deposited onto Cobalt Chromium Cardiovascular Stents

The objective of this study was to evaluate the coating integrity performance and corrosion protection property of trimethylsilane (TMS) plasma nanocoatings that were directly deposited onto cobalt chromium (CoCr) L605 cardiovascular stents. Hydrophilic surfaces were achieved for the TMS plasma nanocoatings that were deposited onto the coronary stents through NH3/O2 (2:1 molar ratio) plasma post-treatment. With a coating thickness of approximately 20-25 nm, the TMS plasma nanocoatings were highly durable and able to resist delamination and cracking from crimping and expansion by a Model CX with a J-Crimp Station. The stent surface that was evaluated by Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) showed no indications of pitting, corrosion, or adsorption products on either the luminal or abluminal surfaces of the stents, in contrast to the uncoated stent surface. The TMS plasma nanocoatings significantly enhanced the stent's corrosion resistance in immersion experiments that followed the ASTM F2129-15 corrosion protocol, evident in the increase of the open circuit potential (OCP) from 0.01 V for the uncoated L605 stent to 0.18 V for the plasma-nanocoated L605 stent, reducing potential cytotoxic metal ion release. Cyclic polarization (CP) curves show that the corrosion rate (density level) observed in plasma-nanocoated L605 stents was approximately half an order of magnitude lower than that of the uncoated stents, indicating improved corrosion protection of the stents. CP curves of the TMS plasma-nanocoated stents with different coating thicknesses show that, in the range of 20-65 nm, the coating thickness does not result in any difference in the corrosion resistance of the stents.

Effect of Si Content on the Thermal Expansion of Ti15Mo(0-2 Si) Biomaterial Alloys during Different Heating Rates

Thermal expansion measurements were used to characterize phase transformations in metastable β-Ti alloys (Ti15MoxSi) without and with various Si additions (where x = 0, 0.5, 1.0, 1.5, and 2 in wt.%) during linear heating at two heating rates of 5 and 10 °C/min up to 850 °C. For this study, five alloys were developed and examined in terms of their presence phases, microstructures, and starting and final transformation temperatures. According to the results, all of the as-cast samples primarily include an equiaxed β-Ti phase. The influence of phase transformation on the material dimensions was discussed and compared with the variations in Si contents. The transformation was investigated using a dilatometric technique for the developed alloys during continuous heating and cooling. The dilatometric curve of heating revealed two distinct reflection points as the heating temperature increased. The starting transformation temperature (T_s) to obtain the ω-phase was reported at 359 °C without Si addition; whereas the final transformation temperature (T_f) of the dissolution of α-phase was obtained at 572 °C at a heating rate of 10 °C/min. At 2 wt.% Si, the first derivative curves reported T_s and T_f transforming temperatures of 314-565 °C (at a 5 °C/min heating rate) and 270-540 °C (at a 10 °C/min heating rate), respectively. The T_s and T_f transforming temperatures were significantly decreased with Si additions, which decreased the β-transus temperature. Moreover, the thermal expansion coefficient curves of the investigated alloys without and with 2 wt.% Si were studied. The transformation heating curves have an S-shaped pattern, according to the results.

Electrochemical and biological characterization of Ti-Nb-Zr-Si alloy for orthopedic applications

The performance of current biomedical titanium alloys is limited by inflammatory and severe inflammatory conditions after implantation. In this study, a novel Ti-Nb-Zr-Si (TNZS) alloy was developed and compared with commercially pure titanium, and Ti-6Al-4V alloy. Electrochemical parameters of specimens were monitored during 1 h and 12 h immersion in phosphate buffered saline (PBS) as a normal, PBS/hydrogen peroxide (H₂O₂) as an inflammatory, and PBS/H₂O₂/albumin/lactate as a severe inflammatory media. The results showed an effect of the H₂O₂ in inflammatory condition and the synergistic behavior of H₂O₂, albumin, and lactate in severe inflammatory condition towards decreasing the corrosion resistance of titanium biomaterials. Electrochemical tests revealed a superior corrosion resistance of the TNZS in all conditions due to the presence of silicide phases. The developed TNZS was tested for subsequent cell culture investigation to understand its biocompatibility nature. It exhibited favorable cell-materials interactions in vitro compared with Ti-6Al-4V. The results suggest that TNZS alloy might be a competitive biomaterial for orthopedic applications.

Investigation of Antibacterial Properties of Corrosion-Resistant 316L Steel Alloyed with 0.2 wt.% and 0.5 wt.% Ag

The article is devoted to the study of melted ingots, plates rolled from them, and the resulting spherical powder made of corrosion-resistant 316L steel with the addition of 0.2 wt.% and 0.5 wt.% Ag. The study of antibacterial properties, microstructure, and distribution of silver concentrations, as well as qualitative analysis of silver content was carried out. The optimal mode of homogenization annealing of the ingot was 1050 °C for 9 h, which leads to the formation of an austenitic structure. It is shown that the addition of a small amount of silver does not affect the formation of the austenitic structure and silver is distributed evenly throughout the volume of the ingot. The austenitic structure also prevails in the plates after rolling. Silver is distributed evenly throughout the entire volume of the plate. It is noted that the addition of 0.2 wt.% Ag does not affect the strength, elongation, and microhardness of steel, and the addition of 0.5 wt.% Ag does not significantly reduce the strength of steel, however, all samples meet the mechanical characteristics according to the ASTM A240 standard. The qualitative chemical composition of samples made of corrosion-resistant steels was confirmed by X-ray fluorescence analysis methods. By the method of energy-dispersion analysis, the presence of a uniform distribution of silver over the entire volume of the powder particle was determined. The particles have a spherical shape with a minimum number of defects. The study of the antibacterial activity of plates and powder shows the presence of a clear antibacterial effect (bacteria of the genus Xanthomonas campestris, Erwinia carotovora, Pseudomonas marginalis, Clavibacter michiganensis) in samples No. 2 and No. 3 with the addition of 0.2 wt.% and 0.5 wt.% Ag.

Biocompatibility of a Zr-Based Metallic Glass Enabled by Additive Manufacturing

The present work explored the use of the selective laser melting (SLM) technique to develop a Zr-based bulk metallic glass (BMG) and investigate the influence of the process parameters on obtaining different levels of surface roughness. Moreover, the potential of the additively manufactured BMG Zr_59.3Cu_28.8Al_10.4Nb_1.5 (trade name AMLOY-ZR01) as an implant material was studied by evaluating the osteoblastic cell response to the alloy and its stability under simulated biological environments. The materials were characterized in terms of degree of crystallinity, surface roughness, and morphology, followed by a systematic investigation of the response of the MC3T3-E1 preosteoblastic cell line to the as-printed samples. The materials supported cell proliferation and differentiation of the preosteoblastic cells, with results comparable to the reference material Ti-6Al-4V. The surface microroughness and surface morphology (porous or groove-type laser tracks) investigated in this study did not have a significant effect on modulating the cell response. Ion release experiments showed a large increase in ion release under inflammatory conditions as compared to regular physiological conditions, which could be attributed to the increased local corrosion under inflammatory conditions. The findings in this work showed that the surface roughness of the additively manufactured BMG AMLOY-ZR01 can be tailored by controlling the laser power applied during the SLM process. The favorable cell response to the as-printed AMLOY-ZR01 represents of a significant advancement of the investigation of additively manufactured BMGs for orthopedic applications, while the results of the ion release study highlights the effect that inflammatory conditions could have on the degradation of the alloy.

Surface Functionalization of Ti6Al4V-ELI Alloy with Antimicrobial Peptide Nisin

Implant-associated infections are a severe global concern, especially in the case of orthopedic implants intended for long-term or permanent use. The traditional treatment through systemic antibiotic administration is often inefficient due to biofilm formation, and concerns regarding the development of highly resistant bacteria. Therefore, there is an unfulfilled need for antibiotic-free alternatives that could simultaneously support bone regeneration and prevent bacterial infection. This study aimed to perform, optimize, and characterize the surface functionalization of Ti6Al4V-ELI discs by an FDA-approved antimicrobial peptide, nisin, known to hold a broad antibacterial spectrum. Accordingly, nisin bioactivity was also evaluated by in vitro release tests both in physiological and inflammatory pH conditions. Several methods, such as X-ray photoelectron spectroscopy (XPS), and Kelvin Probe atomic force microscopy confirmed the presence of a physisorbed nisin layer on the alloy surface. The functionalization performed at pH 6-7 was found to be especially effective due to the nisin configuration exposing its hydrophobic tail outwards, which is also responsible for its antimicrobial action. In addition, the first evidence of gradual nisin release both in physiological and inflammatory conditions was obtained: the static contact angle becomes half of the starting one after 7 days of soaking on the functionalized sample, while it becomes 0° on the control samples. Finally, the evaluation of the antibacterial performance toward the pathogen Staphylococcus aureus after 24 h of inoculation showed the ability of nisin adsorbed at pH 6 to prevent bacterial microfouling into biofilm-like aggregates in comparison with the uncoated specimens: viable bacterial colonies showed a reduction of about 40% with respect to the un-functionalized surface and the formation of (microcolonies (biofilm-like aggregates) is strongly affected.

Preparation and Investigation of Spherical Powder Made from Corrosion-Resistant 316L Steel with the Addition of 0.2% and 0.5% Ag

The paper describes the production and study of spherical powder made from corrosion-resistant 316L steel with the addition of 0.2% and 0.5% Ag. The study of granulometric composition, morphology, fluidity and bulk density, phase composition, microhardness and impurity composition of the spherical powders was carried out. The study showed compliance of the spherical powders with the requirements for powders used for additive manufacturing. The fluidity of the powders was 17.9 s, and the bulk density was 3.76 g/cm³. The particles have a spherical shape with a minimum number of defects and an austenitic-ferritic structure. The study of the phase composition of ingots, wires and powders showed that the ingot structure of all samples consists of austenite. According to the results of studies of the phase composition of the wire, there is a decrease in γ-Fe and an increase in α-Fe and σ-NiCr in going from wire No. 1 to wire No. 3. According to the results of studies of the phase composition of the powder particles, there are three phases, γ-Fe, α-Fe, and Fe₃O₄. The study of microhardness showed a decrease in HV depending on the increase in silver. The hardness of the powder is lower than that of the ingot by 16-24% due to the presence of a ferritic phase in the powder. As a result of plasma spraying, an increase in residual oxygen is observed, which is associated with the oxidation of the melt during plasma dispersion. The amount of nitrogen and sulfur does not change, while the amount of carbon and hydrogen decreases, and the impurities content corresponds to the standards for corrosion-resistant steel. Qualitative and quantitative analysis of the silver content in the samples indicates that it was not affected by the stages involved in obtaining the spherical powder.

Progress in partially degradable titanium-magnesium composites used as biomedical implants

Titanium-magnesium composites have gained increasing attention as a partially degradable biomaterial recently. The titanium-magnesium composite combines the bioactivity of magnesium and the good mechanical properties of titanium. Here, we discuss the limitations of conventional mechanically alloyed titanium-magnesium alloys for bioimplants, in addition we summarize three suitable methods for the preparation of titanium-magnesium composites for bioimplants by melt: infiltration casting, powder metallurgy and hot rotary swaging, with a description of the advantages and disadvantages of all three methods. The titanium-magnesium composites were comprehensively evaluated in terms of mechanical properties and degradation behavior. The feasibility of titanium-magnesium composites as bio-implants was reviewed. In addition, the possible future development of titanium-magnesium composites was discussed. Thus, this review aims to build a conceptual and practical toolkit for the design of titanium-magnesium composites capable of local biodegradation.

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.

Addressing the Needs of the Rapidly Aging Society through the Development of Multifunctional Bioactive Coatings for Orthopedic Applications

The unprecedented aging of the world's population will boost the need for orthopedic implants and expose their current limitations to a greater extent due to the medical complexity of elderly patients and longer indwelling times of the implanted materials. Biocompatible metals with multifunctional bioactive coatings promise to provide the means for the controlled and tailorable release of different medications for patient-specific treatment while prolonging the material's lifespan and thus improving the surgical outcome. The objective of this work is to provide a review of several groups of biocompatible materials that might be utilized as constituents for the development of multifunctional bioactive coatings on metal materials with a focus on antimicrobial, pain-relieving, and anticoagulant properties. Moreover, the review presents a summary of medications used in clinical settings, the disadvantages of the commercially available products, and insight into the latest development strategies. For a more successful translation of such research into clinical practice, extensive knowledge of the chemical interactions between the components and a detailed understanding of the properties and mechanisms of biological matter are required. Moreover, the cost-efficiency of the surface treatment should be considered in the development process.

Polyphenols from Grape Pomace: Functionalization of Chitosan-Coated Hydroxyapatite for Modulated Swelling and Release of Polyphenols

Chitosan is known for its specific antibacterial mechanism and biodegradability, while polyphenols are known for their antioxidant and anti-inflammatory properties: coupling these properties on a surface for bone contact, such as hydroxyapatite, is of great interest. The system developed here allows the combination of hydroxyapatite, chitosan, and polyphenol properties in the same multifunctional biomaterial in order to modulate the host response after implantation. Crosslinked chitosan is used in this research to create a stable coating on hydroxyapatite, and then it is functionalized for a smart release of the polyphenols. The release is higher in inflammatory conditions and lower in physiological conditions. The properties of the coated and functionalized samples are characterized on the as-prepared samples and after the samples are immersed (for 24 h) in solutions, which simulate the inflammatory and physiological conditions. Characterization is performed in order to confirm the presence of polyphenols grafted within the chitosan coating, the stability of grafting as a function of pH, the morphology of the coating and distribution of polyphenols on the surface, and the redox reactivity and radical scavenging activity of the functionalized coating. All the results are in line with previous results, which show a successful coating with chitosan and functionalization with polyphenols. Moreover, the polyphenols have a different release kinetics that is faster in a simulated inflammatory environment compared to that in the physiological environment. Even after the release tests, a fraction of polyphenols are still bound on the surface, maintaining the antioxidant and radical scavenging activity for a longer time. An electrostatic bond occurs between the negative-charged polar groups of polyphenols (carboxyls and/or phenols) and the positive amide groups of the chitosan coating, and the substitution of the crosslinker by the polyphenols occurs during the functionalization process.

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.

In vivo performance of Al2O3-Ti bone implants in the rat femur

Background

Alumina-titanium (Al₂O₃-Ti) biocomposites have been recently developed with improved mechanical properties for use in heavily loaded orthopedic sites. Their biological performance, however, has not been investigated yet.

Methods

The aim of the present study was to evaluate the in vivo biological interaction of Al₂O₃-Ti. Spark plasma sintering (SPS) was used to fabricate Al₂O₃-Ti composites with 25 vol.%, 50 vol.%, and 75 vol.% Ti content. Pure alumina and titanium were also fabricated by the same procedure for comparison. The fabricated composite disks were cut into small bars and implanted into medullary canals of rat femurs. The histological analysis and scanning electron microscopy (SEM) observation were carried out to determine the bone formation ability of these materials and to evaluate the bone-implant interfaces.

Results

The histological observation showed the formation of osteoblast, osteocytes with lacuna, bone with lamellar structures, and blood vessels indicating that the healing and remodeling of the bone, and vasculature reconstruction occurred after 4 and 8 weeks of implantation. However, superior bone formation and maturation were obtained after 8 weeks. SEM images also showed stronger interfaces at week 8. There were differences between the composites in percentages of bone area (TB%) and the number of osteocytes. The 50Ti composite showed higher TB% at week 4, while 25Ti and 75Ti represented higher TB% at week 8. All the composites showed a higher number of osteocytes compared to 100Ti, particularly 75Ti.

Conclusions

The fabricated composites have the potential to be used in load-bearing orthopedic applications.

Effects of Ag-Rich Nano-Precipitates on the Antibacterial Properties of 2205 Duplex Stainless Steel

The effects of the addition of silver on the microstructural variation and antibacterial performance of 2205 duplex stainless steel after solution and aging treatment were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, and antibacterial testing. The microstructure showed that 2205Ag is composed of a ferrite (α) + austenite (γ) duplex phase and Ag-rich nano-precipitates (Ag-NPs). The morphology of the Ag-NPs varied from spherical to polygonal after aging treatment at 450 °C for 4 h. These precipitates were identified as face-centered-cubic structures with a lattice parameter of a = 0.354 nm and a mismatch of δ = 0.84% relative to the austenite matrix. Notably, 2205Ag with polygonal Ag-NPs exhibited excellent antibacterial properties that were superior to those of 2205Ag with spherical Ag-NPs.

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.

Evolution of metallic cardiovascular stent materials: A comparative study among stainless steel, magnesium and zinc

A cardiovascular stent is a small mesh tube that expands a narrowed or blocked coronary artery. Unfortunately, current stents, regardless metallic or polymeric, still largely fall short to the ideal clinical needs due to late restenosis, thrombosis and other clinical complications. Nonetheless, metallic stents are preferred clinically thanks to their superior mechanical property and radiopacity to their polymeric counterparts. The emergence of bioresorbable metals opens a window for better stent materials as they may have the potential to reduce or eliminate late restenosis and thrombosis. In fact, some bioresorbable magnesium (Mg)-based stents have obtained regulatory approval or under trials with mixed clinical outcomes. Some major issues with Mg include the too rapid degradation rate and late restenosis. To mitigate these problems, bioresorbable zinc (Zn)-based stent materials are being developed lately with the more suitable degradation rate and better biocompatibility. The past decades have witnessed the unprecedented evolution of metallic stent materials from first generation represented by stainless steel (SS), to second generation represented by Mg, and to third generation represented by Zn. To further elucidate their pros and cons as metallic stent materials, we systematically evaluated their performances in vitro and in vivo through direct side-by-side comparisons. Our results demonstrated that tailored Zn-based material with proper configurations could be a promising candidate for a better stent material in the future.

Stability of PMMA-grafted/Ti hybrid biomaterial interface in corrosive media

The stability of interfaces between polymethyl methacrylate (PMMA) and titanium (Ti) are tested in a Ringer solution that is an aggressive medium usually used for biomaterial evaluation. The devices are PMMA-grafted/Ti elaborated via a “grafting-from” method involving three steps, the alkali activation of Ti sheets, their functionalization with an initiator of polymerization through a phosphonate anchoring group and the growth of PMMA brushes. Electrochemical characterizations demonstrate that the stability of the PMMA-grafted/Ti interface in biological medium is satisfactory and that the grafting of PMMA is even acting as a protective barrier for titanium. Indeed, PMMA-grafted/Ti remains passive in Ringer solution until at least +3 V/SCE (saturated calomel electrode), even under inflammatory conditions, while localized corrosion was measured on as-received titanium in similar conditions. This protecting role is attributed to the grafted interface, since spin-coated PMMA does not decrease the corrosion sensitivity of titanium.

Effect of the coexistence of albumin and H2O2 on the corrosion of biomedical cobalt alloys in physiological saline

The corrosion of Co-28Cr-6Mo and Co-35Ni-20Cr-10Mo, as biomedical alloys, has been investigated for effects of typical species (albumin and H2O2) in physiological saline, with their coexistence explored for the first time. Electrochemical and long term immersion tests were carried out. It was found that Co alloys were not sensitive to the presence of albumin alone, which slightly promoted anodic dissolution of Co-35Ni-20Cr-10Mo without noticeably affecting Co-28Cr-6Mo and facilitated oxide film dissolution on both alloys. H2O2 led to a clear drop in corrosion resistance, favouring metal release and surface oxide formation and inducing much thicker but less compact oxide films for both alloys. The coexistence of both species resulted in the worst corrosion resistance and most metal release, while the amount and composition of surface oxide remained at a similar level as in the absence of both. The effect of H2O2 inducing low compactness of surface oxides should prevail on deciding the poor corrosion protection ability of passive film, while albumin simultaneously promoted dissolution or inhibited formation of oxides due to H2O2. Corrosion resistance was consistently lower for Co-35Ni-20Cr-10Mo under each condition, the only alloy where the synergistic effect of both species was clearly demonstrated. This work suggests that the complexity of the environment must be considered for corrosion resistance evaluation of biomedical alloys.

Fretting initiated crevice corrosion of 316LVM stainless steel in physiological phosphate buffered saline: Potential and cycles to initiation

Mechanically assisted crevice corrosion (MACC) has been associated with implant failure in vivo and is a serious concern in numerous metallic implant systems. Stainless steel medical devices may be subjected to fretting and crevice corrosion in the human body as are titanium and CoCrMo alloys due to the presence of a passive oxide film on their surface. One mechanism of MACC that has not been clearly identified and studied is fretting-initiated crevice corrosion (FICC) of stainless steel where an initial fretting event can initiate a rapid propagating crevice corrosion process even when fretting has ceased. FICC pin-on-disk experiments were performed at varying potential conditions and duration of fretting to explore the role of potential and fretting duration on the initiation of crevice corrosion. Triggering of a propagating crevice corrosion reaction on stainless steel at 250 mV vs Ag/AgCl/KCl (saturated) in PBS solution required only 2 s (2 cycles at 1 Hz) of fretting. Crevice corrosion continued to propagate under a 1.8 mm diameter pin with only 100 μm of direct contact, dissolving in both the depth and width dimension away from the fretting contact while the currents rose from 0.2 μA to 15 μA within 5 min. Three different potential-dependent FICC regions were identified that included unstable crevice corrosion (50 mV and above), metastable crevice corrosion (-100 mV to 0 mV) and stable fretting corrosion (between -500 mV and -150 mV). Crevice corrosion can be induced by fretting at potentials as low as -100 mV. Below -100 mV, there was no FICC, but rather fretting corrosion stopped immediately after fretting ceased and returned to a stable baseline current. Metastable FICC was shown at potentials between -100 mV and 0 mV, when the crevice corrosion current gradually decreased over several seconds or longer after fretting ceased. Self-sustained, unstable crevice corrosion started at 50 mV, where prior to fretting the currents were low, and after just a few cycles of fretting the crevice current rose rapidly and continued to increase after fretting stopped. Increase of potential increased the susceptibility of stainless steel to FICC. Scanning electron microscopy and digital optical microscopy revealed pitting and crevice corrosion on samples at -100 mV and higher potentials, where FICC was developing. By removing the oxide film, fretting motion significantly facilitates the critical crevice solution development, lowering the critical crevice potential and decreasing the initiation time for crevice corrosion. These results indicate that fretting initiated crevice corrosion may affect the performance of stainless steel in vivo. STATEMENT OF SIGNIFICANCE: AISI 316L stainless steel has been widely used as a metallic biomaterial for orthopaedic, spinal, dental and cardiovascular implants. Crevice corrosion has been a serious concern for stainless steel implants. For the first time we demonstrated and systematically studied the process of fretting-initiated crevice corrosion (FICC) in 316L stainless steel in simulated physiological solution of phosphate buffered saline. By removing the oxide film, fretting motion significantly facilitates the critical crevice solution development, lowering the critical crevice potential and decreasing the initiation time for crevice corrosion. Our findings indicate fundamental differences between the FICC mechanism and conventional crevice corrosion theory, showing that fretting can play a significant role in the initiation of crevice corrosion of stainless steel.

Comparison of ASTM F2129 and ASTM F746 for Evaluating Crevice Corrosion

Crevice corrosion is one of the major mechanisms that drives implant failure in orthopedic devices that have modular interfaces. Despite the prevalence of crevice corrosion in modular interfaces, very little is known with regards to the susceptibility of different material combinations to participate in crevice corrosion. In this study, we compare two electrochemical methods, ASTM F2129, Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements to Determine the Corrosion Susceptibility of Small Implant Devices, and a modified version of ASTM F746, Standard Test Method for Pitting or Crevice Corrosion of Metallic Surgical Implant Materials, in their ability to induce crevice corrosion. Four commonly used metals, 316 stainless steel, commercially pure titanium (Ti grade 2), Ti-6Al-4V (Ti grade 5), and cobalt-chromium-molybdenum per ASTM F1537, Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNSR31537, UNSR31538, and UNSR31539), were used to form crevices with a rod and washer combination. As a control, the metal rod materials were tested alone in the absence of crevices using ASTM F2129 and the modified ASTM F746 method. As another control to determine if crevices formed with polymeric materials would influence crevice corrosion susceptibility, experiments were also conducted with metal rods and polytetrafluorethylene washers. Our results revealed more visible corrosion after ASTM F2129 than ASTM F746. Additionally, ASTM F746 was found to falsely identify crevice corrosion per the critical pitting potential when visual inspection found no evidence of crevice corrosion. Hence, ASTM F2129 was found to be more effective overall at evaluating crevice corrosion compared to ASTM F746.

Corrosion of Al2O3-Ti composites under inflammatory condition in simulated physiological solution

Alumina-titanium composites have shown good mechanical properties which makes them promising for orthopedic applications. The placement of an orthopedic implant involves an invasive procedure which stimulates a localized inflammatory response causing an acidic environment around the implant. This makes the study on corrosion more critical. Therefore, the aim of the present paper was to study the corrosion behavior of the composites with 75 vol% and 50 vol% Ti content (with alumina balance) fabricated by Spark Plasma Sintering under acidic condition representing inflammation and in two elapsed times (1 h and 1-day) using polarization and electrochemical impedance spectroscopy tests. For comparison, the experiments were also conducted in normal physiological solution after 1 h, and pure Ti (100vol%Ti) was fabricated by the same process and analyzed, similarly. Furthermore, behavior of the samples was studied after 48 days of immersion in the acidic and normal solutions using SEM, ATR-FTIR, AFM, and ICP-OES. The results of corrosion tests showed very good passivation behavior of 100vol%Ti and the composite containing 75vol.%Ti. The superiority of the 75vol.%Ti composite in corrosion characteristics in both solutions was also found. Its corrosion resistance was 20.3 MΩcm² under the inflammatory condition after 1-day, which was 39% higher than that of 100vol.%Ti under the same condition. The results of SEM indicated both corroded and mineral deposition zones on all materials' surfaces and the ATR-FTIR results revealed additional adsorbed bands related to water adsorption, OH and carbonate groups after immersion. The AFM analysis showed rougher morphology, particularly for 75 vol% Ti where the Rq was increased about 50 nm, and the ICP-OES results indicated 65.87% and 61.94% deposition of solution calcium on 75vol.%Ti and 50vol.%Ti, respectively. The acidic/inflammatory condition influenced the corrosion processes of all materials. Lower pH caused the passivation to occur sooner and the corrosion resistance to be higher.

Time-dependent Enhanced Corrosion of Ti6Al4V in the Presence of H2O2 and Albumin

There is increasing concern regarding the biological consequences of metal release from implants. However, the mechanisms underpinning implant surface degradation, especially in the absence of wear, are often poorly understood. Here the synergistic effect of albumin and H₂O₂ on corrosion of Ti6Al4V in physiological saline is studied with electrochemical methods. It is found that albumin induces a time-dependent dissolution of Ti6Al4V in the presence of H₂O₂ in physiology saline. Potentiostatic polarisation measurements show that albumin supresses dissolution in the presence of H₂O₂ at short times (<24 h) but over longer time periods (120 h) it significantly accelerates corrosion, which is attributed to albumin-catalysed dissolution of the corrosion product layer resulting in formation of a thinner oxide film. Dissolution of Ti6Al4V in the presence of albumin and H₂O₂ in physiological saline is also found to be dependent on potential: the titanium ion release rate is found to be higher (0.57 µg/cm²) at a lower potential (90 mV), where the oxide capacitance and resistance inferred from Electrochemical Impedance Spectroscopy also suggests a less resistant oxide film. The study highlights the importance of using more realistic solutions, and considering behaviour over longer time periods when testing corrosion resistance of metallic biomaterials.