Increasing temperature accelerates Ti-6Al-4V oxide degradation and selective dissolution: An Arrhenius-based analysis.

Ti-6Al-4V selective dissolution occurs in vivo on orthopedic implants as the leading edge of a pitting corrosion attack. A gap persists in our fundamental understanding of selective dissolution and pre-clinical tests fail to reproduce this damage. While CoCrMo clinical use decreases, Ti-6Al-4V and the crevice geometries where corrosion can occur remain ubiquitous in implant design. Additionally, most additively manufactured devices cleared by the FDA use Ti-6Al-4V. Accelerated preclinical testing, therefore, would aid in the evaluation of new titanium devices and biomaterials. In this study, using temperature, we (1) developed an accelerated pre-clinical methodology to rapidly induce dissolution and (2) investigated the structure-property relationship between the dissolving surface and the oxide layer. We hypothesized that solution temperature and H2O2 concentration would accelerate oxide degradation, increase corrosion kinetics and decrease experimental times. To assess this effect, we selected temperatures above (45 °C), below (24 °C), and at (37 °C) physiological levels. Then, we acquired electrochemical impedance spectra during active ß dissolution, showing significant decreases in oxide polarization resistance (Rp) both over time (p = 0.000) and as temperature increased (p = 0.000). Next, using the impedance response as a guide, we quantified the extent of selective dissolution in scanning electron micrographs. As the temperature increased, the corrosion rate increased in an Arrhenius-dependent manner. Last, we identified three surface classes as the oxide properties changed: undissolved, transition and dissolved. These results indicate a concentration and temperature dependent structure-property relationship between the solution, the protective oxide film, and the substrate alloy. Additionally, we show how supraphysiological temperatures induce structurally similar dissolution to tests run at 37 °C in less experimental time. STATEMENT OF SIGNIFICANCE: Within modular taper junctions of total hip replacement systems, retrieval studies document severe corrosion including Ti-6AL-4V selective dissolution. Current pre-clinical tests and ASTM standards fail to reproduce this damage, preventing accurate screening of titanium-based biomaterials and implant designs. In this study, we induce selective dissolution using accelerated temperatures. Building off previous work, we use electrochemical impedance spectroscopy to rapidly monitor the oxide film during dissolution. We elucidate components of the dissolution mechanism, where oxide degradation precedes pit nucleation within the ß phase. Using an Arrhenius approach, we relate these accelerated testing conditions to more physiologically relevant solution concentrations. In total, this study shows the importance of including adverse electrochemical events like cathodic activation and inflammatory species in pre-clinical testing.

Fretting and Fretting Corrosion Behavior of Additively Manufactured Ti-6Al-4V and Ti-Nb-Zr Alloys in Air and Physiological Solutions.

Additive manufacturing (AM) of orthopedic implants has increased in recent years, providing benefits to surgeons, patients, and implant companies. Both traditional and new titanium alloys are under consideration for AM-manufactured implants. However, concerns remain about their wear and corrosion (tribocorrosion) performance. In this study, the effects of fretting corrosion were investigated on AM Ti-29Nb-21Zr (pre-alloyed and admixed) and AM Ti-6Al-4V with 1% nano yttria-stabilized zirconia (nYSZ). Low cycle (100 cycles, 3 Hz, 100 mN) fretting and fretting corrosion (potentiostatic, 0 V vs. Ag/AgCl) methods were used to compare these AM alloys to traditionally manufactured AM Ti-6Al-4V. Alloy and admixture surfaces were subjected to (1) fretting in the air (i.e., small-scale reciprocal sliding) and (2) fretting corrosion in phosphate-buffered saline (PBS) using a single diamond asperity (17 µm radius). Wear track depth measurements, fretting currents and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of oxide debris revealed that pre-alloyed AM Ti-29Nb-21Zr generally had greater wear depths after 100 cycles (4.67 +/- 0.55 µm dry and 5.78 +/- 0.83 µm in solution) and higher fretting currents (0.58 +/- 0.07 µA). A correlation (R2 = 0.67) was found between wear depth and the average fretting currents with different alloys located in different regions of the relationship. No statistically significant differences were observed in wear depth between in-air and in-PBS tests. However, significantly higher amounts of oxygen (measured by oxygen weight % by EDS analysis of the debris) were embedded within the wear track for tests performed in PBS compared to air for all samples except the ad-mixed Ti-29Nb-21Zr (p = 0.21). For traditional and AM Ti-6Al-4V, the wear track depths (dry fretting: 2.90 +/- 0.32 µm vs. 2.51 +/- 0.51 µm, respectively; fretting corrosion: 2.09 +/- 0.59 µm vs. 1.16 +/- 0.79 µm, respectively) and fretting current measurements (0.37 +/- 0.05 µA vs. 0.34 +/- 0.05 µA, respectively) showed no significant differences. The dominant wear deformation process was plastic deformation followed by cyclic extrusion of plate-like wear debris at the end of the stroke, resulting in ribbon-like extruded material for all alloys. While previous work documented improved corrosion resistance of Ti-29Nb-21Zr in simulated inflammatory solutions over Ti-6Al-4V, this work does not show similar improvements in the relative fretting corrosion resistance of these alloys compared to Ti-6Al-4V.

Oxide degradation precedes additively manufactured Ti-6Al-4V selective dissolution: An unsupervised machine learning correlation of impedance and dissolution compared to Ti-29Nb-21Zr.

Additively manufactured (AM) Ti-6Al-4V devices are implanted with increasing frequency. While registry data report short-term success, a gap persists in our understanding of long-term AM Ti-6Al-4V corrosion behavior. Retrieval studies document ß phase selective dissolution on conventionally manufactured Ti-6Al-4V devices. Researchers reproduce this damage in vitro by combining negative potentials (cathodic activation) and inflammatory simulating solutions (H2 O2 -phosphate buffered saline). In this study, we investigate the effects of these adverse electrochemical conditions on AM Ti-6Al-4V impedance and selective dissolution. We hypothesize that cathodic activation and H2 O2 solution will degrade the oxide, promoting corrosion. First, we characterized AM Ti-6Al-4V samples before and after a 48 h -0.4 V hold in 0.1 M H2 O2 /phosphate buffered saline. Next, we acquired nearfield electrochemical impedance spectroscopy (EIS) data. Finally, we captured micrographs and EIS during dissolution. Throughout, we used AM Ti-29Nb-21Zr as a comparison. After 48 h, AM Ti-6Al-4V selectively dissolved. Ti-29Nb-21Zr visually corroded less. Structural changes at the AM Ti-6Al-4V oxide interface manifested as property changes to the impedance. After dissolution, the log-adjusted constant phase element (CPE) parameter, Q, significantly increased from -4.75 to -3.84 (Scm-2 (s)α ) (p = .000). The CPE exponent, α, significantly decreased from .90 to .84 (p = .000). Next, we documented a systematic decrease in oxide polarization resistance before pit nucleation and growth. Last, using k-means clustering, we established a structure-property relationship between impedance and the surface's dissolution state. These results suggest that AM Ti-6Al-4V may be susceptible to in vivo crevice corrosion within modular taper junctions.

Additively manufactured Ti-29Nb-21Zr shows improved oxide polarization resistance versus Ti-6Al-4V in inflammatory simulating solution.

Retrieval studies in the past two decades show severe corrosion of titanium and its alloys in orthopedic implants. This damage is promoted by mechanically assisted crevice corrosion (MACC), particularly within modular titanium-titanium junctions. During MACC, titanium interfaces may be subject to negative potentials and reactive oxygen species (ROS), generated from cathodic activation and/or inflammation. Additive manufacturing (AM) may be able to produce new, corrosion-resistant titanium alloys and admixtures that are less susceptible to these adverse electrochemical events. In this study, we characterize the impedance and corrosion properties of three new AM titanium materials, including Ti-6Al-4V with added 1% nano-yttria stabilized ZrO2 , admixed Ti-29Nb-21Zr, and pre-alloyed Ti-29Nb-21Zr. We aim to elucidate how these materials perform when subjected to high ROS solutions. We include conventionally and additively manufactured Ti-6Al-4V in our study as comparison groups. A 0.1 M H2 O2 phosphate-buffered saline (PBS) solution, simulating inflammatory conditions, significantly increased biomaterial OCP (-0.14 V vs. Ag/AgCl) compared to PBS only (-0.38 V, p = .000). During anodic polarization, Ti-6Al-4V passive current density more than doubled from 1.28 × 10-7 to 3.81 × 10-7 A/cm2 when exposed to 0.1 M H2 O2 . In contrast, Ti-29Nb-21Zr passive current density remained relatively unchanged, slightly increasing from 7.49 × 10-8 in PBS to 9.31 × 10-8 in 0.1 M H2 O2 . Ti-29Nb-21Zr oxide polarization resistance (Rp ) was not affected by 0.1 M H2 O2 , maintaining a high value (1.09 × 106 vs. 1.89 × 106 Ω cm2 ), while Ti-6Al-4V in 0.1 M H2 O2 solution had significantly diminished Rp (4.38 × 106 in PBS vs. 7.24 × 104 Ω cm2 in H2 O2 ). These results indicate that Ti-29Nb-21Zr has improved corrosion resistance in ROS containing solutions when compared with Ti-6Al-4V based biomaterials.

Low cycle fretting and fretting corrosion properties of low carbon CoCrMo and additively manufactured CoCrMoW alloys for dental and orthopedic applications.

Additive manufacturing (AM) of CoCrMo metallic implants is growing in the orthopedic and dental fields. This is due to the traditional alloy's excellent corrosion resistance and mechanical properties. AM processes like selective laser melting (SLM) require less time, materials, and waste than casting or subtractive manufacturing complex-geometry structures (bridges, partial dentures, etc.). The objective of this work was to investigate the low cycle tribological and tribocorrosion characteristics of AM CoCrMoW alloys compared to wrought LC CoCrMo (ASTM F-1537) to assess this AM alloy's performance. Fretting and tribocorrosion testing was performed in air (wear only), PBS (wear + corrosion), and PBS with 10 mM H2 O2 (wear + corrosion + inflammation) by a single diamond asperity. No variation between alloys in volume of material removed (p = .12), volume of plastic deformation (p = .13), and scratch depth (p = .84) showed that AM was substantially similar in wear resistance to LC in air and PBS. AM exhibited significantly higher fretting currents (p < .01) at loads up to 100 mN ( I AM PBS = 57 nA and I AM H 2 O 2 = 49 nA) than LC CoCrMo ( I LC PBS = 30 nA) and ( I LC H 2 O 2 = 29 nA). In PBS, wear track depth linearly correlates to fretting current, averaged over 100 cycles. Additionally, fretting currents of both alloys were significantly lower in simulated inflammatory conditions compared to PBS alone. AM alloy has generally similar wear and tribocorrosion resistance to wrought LC CoCrMo and would be ideal for patient specific dentistry or orthopedics where precise, complex geometries are required.

Retrieval analysis of the Essure® micro insert female sterilization implant: Methods for metal ion and microscopic analysis.

The Essure® Device is a female sterilization implant comprised of four alloys (Ni-Ti, 316L SS, Pt-Ir and Sn-Ag) and Dacron fibers. As part of the mandated 522 post-market surveillance study, implant retrieval and metal-ion analysis methods were developed separate from patient clinical data, to quantify trace metal ions found in tissue and to assess implant degradation present. Three segments of tissue (proximal implant, distal implant, and tissue distal from the implant) stored in neutral buffered formalin, were retrieved. Tissue was prepared for metal ion analysis using inductively coupled mass spectrometry (ICP-MS). Implant sections from four patients, were analyzed using digital optical microscopy (DOM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Image analysis showed Sn-Ag solder corroded and elevated Sn ion levels in tissue proximal to the solder compared to tissues more remote in all cases observed. The 316L SS exhibited signs of degradation with high surface concentrations of molybdenum and chromium and low iron compared to the parent alloy. Evidence of elevated iron, chromium and nickel within the tissues and storage solutions combined with precipitation of an iron-calcium-phosphorous material on some implants indicate evidence of SS corrosion. Ni-Ti, Pt-Ir and Dacron appear to have no major damage. This study includes preliminary results as part of the ongoing 522 study and therefore no final conclusions regarding the device or patient data can be drawn from this present study until the entire 522 study is complete. STATEMENT OF SIGNIFICANCE: The Essure Device is a female sterilization implant that was implanted into approximately 750,000 women. The device is composed of polyethylene terephthalate fibers and 4 metal alloys, 316L stainless steel, Nickel-Titanium, Tin-Silver and Platinum-Iridium. Following an increase in patient reported adverse events, the FDA required a 522-post market surveillance study. As part of this study, implants are retrieved from patients via salpingectomy or hysterectomy. This study focuses on the development of the implant retrieval methods following surgery, with focus on measuring local tissue metal ions, their distribution and assessing the degradation of the implant without correlation to patient clinical condition.

Predicting Corrosion Damage in the Human Body Using Artificial Intelligence: In Vitro Progress and Future Applications.

Artificial intelligence (AI) is used in the clinic to improve patient care. While the successes illustrate AI's impact, few studies have led to improved clinical outcomes. In this review, we focus on how AI models implemented in nonorthopedic fields of corrosion science may apply to the study of orthopedic alloys. We first define and introduce fundamental AI concepts and models, as well as physiologically relevant corrosion damage modes. We then systematically review the corrosion/AI literature. Finally, we identify several AI models that may be implemented to study fretting, crevice, and pitting corrosion of titanium and cobalt chrome alloys.

Fretting corrosion testing of acetabular modular tapers for total hip replacements: A comparison of two designs.

Acetabular components (DePuy Pinnacle (A) and Stryker Trident (B), Ti-6Al-4V shells and CoCrMo liners) with varying geometries were assembled under a 4 kN seating load. Liner-displacement was recorded. Cyclic compression to 4 kN, R = 0.01, 9 Hz was applied for three million cycles to evaluate fretting corrosion currents (n = 5). Fretting currents, load-displacement, ion dissolution, and disassembly loads were used to compare device performance. Data were analyzed using ANOVA with Tukey post hoc comparisons (p < 0.05). Liner seating displacements were not significantly different between groups. Fretting currents averaged over the initial 10 h and over three million cycles were 0.17 µA (A) and 0.55 µA (B) and 0.05 µA (A) and 0.17 µA (B), respectively (p = 0.19). No variation in ion averages between A and B (0.23 and 0.45 ppm for Ti [p = 0.21], 0.63 and 0.85 ppm for Co [p = 0.47]) existed. Average push-out forces, -2.41 (A) and -2.42 kN (B), were not significantly different (p = 0.97). SEM and EDS showed some titanium and metal oxide transfer from the shell to the liner in both designs. Overall, both implant designs exhibited very minor MACC in these experiments. This study demonstrates quantitative measures of in vitro fretting corrosion over the course of three million cycles and the minimal degree of acetabular taper damage. Clinical Significance: Retrieval studies show dual mobility acetabular shell-liner tapers with metal-on-metal contacts are susceptible to fretting corrosion in vivo.

A mass balance analysis of the tribocorrosion process of titanium alloys using a single micro-asperity: Voltage and solution effects on plastic deformation, oxide repassivation, and ion dissolution.

Within modular taper junctions of total hip implants (THA), nominally "smooth" metallic surfaces contain multiple micro-asperities that slide, are plastically deformed, have their oxide film surfaces disrupted and corrode during the fretting corrosion processes. In this work, a mass/volume balance approach is developed and used to assess the contribution of individual components of wear and corrosion to the entirety of the single-asperity tribocorrosion process for the popular THA alloy, Ti-6Al-4V. This analysis measures the total volume change (trough) in the surface due to low cycle single asperity fretting corrosion and compares it to the measured pileup volume which is comprised of plastic deformation, metal particles and oxide particles, plus the fretting current and the concentration of solution-bound species. A simple 17 µm spherical geometry diamond asperity was used and the trough volume, pileup volume, fretting currents and ion concentrations were measured to assess their contribution to the fretting corrosion process. The effects fretting in or out of solution (phosphate buffered saline), and the role of electrode potential, e.g., freely corroding or forced potential (-1.0 V, 0 V, and +1.0 V vs Ag/AgCl) were investigated. Under constant 30 mN loading, 100 cycles duration, 3 Hz cyclic frequency and 80 µm sliding amplitude, the volume abraded, fretting currents, ion release, and pileup volume were all recorded. Damage was analyzed and quantified using digital optical microscopy (DOM), atomic force microscopy (AFM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and inductive coupled plasma mass spectrometry (ICP-MS). The results were analyzed with ANOVA statistics (α = 0.05). The extent of wear damage (asperity trough volume) is as follows: air = Ecorr, air > -1.0 V = 0 V = +1.0 V. As the amount of pileup volume decreased between conditions, visible oxide generation increased, with V > 0 V having more oxide debris generation and air fretting resulting in the least oxide (and most plastic deformation). Ions in solution were not significant, accounting for less than 1% of the damage. Volume analysis showed trough volumes and pileup volumes were very close to one another and were dominated by plastic deformation. Synergy between wear and corrosion were not observed in this work.

Cathodic activation and inflammatory species are critical to simulating in vivo Ti-6Al-4V selective dissolution.

In vivo retrievals of metallic orthopedic implants have shown selective dissolution of Ti-6Al-4V, where the vanadium-rich ß phase preferentially corrodes from the surface. This damage, typically observed in crevices, is not directly caused by wear mechanics and the underlying electrochemical mechanism remains poorly understood. Previous studies show that fretting corrosion can cause negative potential drops, resulting in a decrease in surface oxide passivation resistance and the electrochemical generation of reactive oxygen species (ROS) at metallic surfaces. In this study, we combine cathodic activation and hydrogen peroxide to induce selective dissolution in vitro. After a 600 s -1 V hold and 4 h recovery in 20 °C 1 M H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; solution, the Ti-6Al-4V ß phase was preferentially dissolved. An initial activation threshold of -0.5 V induced a significant increase in ß dissolution (p = 0.000). Above this threshold, little selective dissolution occurred. In an Arrhenius-like fashion, decreasing solution concentration to 0.1 M required 72 h to generate ß dissolution instead of 4 h at 1 M. Heating 0.1 M solution to body temperature (37 °C) resulted in a decrease in the time needed to replicate a similar level of ß dissolution (&amp;gt;90%). Electrochemical impedance shows that both cathodic activation and inflammatory species are necessary to induce selective dissolution, where the combinatorial effect causes a significant drop in oxide passivation resistance from 10&lt;sup&gt;6&lt;/sup&gt; to 10&lt;sup&gt;2&lt;/sup&gt; (p = 0.000). STATEMENT OF SIGNIFICANCE: Though hip arthroplasties are considered a successful procedure, revision rates of 2-4% result in tens of thousands of additional surgeries within the United States, subjecting patients to increased risk of complications. Corrosion is associated with implant failure and retrieval studies show that titanium and its alloys can severely corrode in vivo in ways not yet duplicated in vitro. Here, we reproduce selective dissolution of Ti-6Al-4V ß phase simulating key characteristics of in vivo degradation observed in orthopedic retrievals. We establish both cathodically activated corrosion, a relatively unexplored concept, and the presence of inflammatory species as prerequisites, furthering our understanding of this clinically relevant damage mode. We introduce an Arrhenius-based approach to assess the concentration-temperature-time interactions present.

Corrosion properties of low carbon CoCrMo and additively manufactured CoCr alloys for dental applications.

OBJECTIVES: Additive manufacturing (AM) is being applied to metallic biomaterials and dental alloys, including CoCrMo. CoCrMo mechanical properties and corrosion resistance are vital to the structural integrity of implants and dental appliances. The goal of this work is to assess the resistivity of AM cobalt chromium alloys by comparing them with traditional CoCrMo, regarding electrochemical properties resulting from microstructural and oxide film differences. METHODS: In this work, selective laser melting (SLM), was used to manufacture CoCrMoW. The corrosion characteristics of AM alloy were compared to that of wrought LC CoCrMo (ASTM F-1537) in both phosphate buffered saline (PBS) and PBS with 10 mM H2O2 to simulate increased inflammatory conditions. Anodic polarization and electrochemical impedance spectroscopy (EIS) were performed. RESULTS: Both alloys were substantially similar in corrosion behavior in both solutions. They exhibited changes with the different solutions. Polarization resistances were statistically lower (RpAM = 1.4 MΩcm2 (PBS) vs. 0.72 MΩcm2 (H2O2), RpLC = 1.86 MΩcm2 (PBS) vs. 0.55 MΩcm2 (H2O2)), and open circuit potentials (OCP's) were statistically higher in 10 mM H2O2 for both alloys (0.20 V (in H2O2) vs. - 0.09 V in PBS). Chemistry variations were revealed by the corrosion tests indicating that wrought LC CoCrMo retained its casting-based chemical heterogeneity, while AM CoCrMoW had sub-cell structures within the solidified grains. SIGNIFICANCE: As novel production methods like AM arise, it is necessary to understand any microstructural differences that may diminish the corrosion resistance properties. AM CoCrMoW alloys hold significant promise for use in dentistry where complex geometries are required.

In Vitro Corrosion Assessment of the Essure® Medical Device in Saline, Simulated Inflammatory Solution and Neutral Buffered Formalin.

The Essure® permanent contraceptive implant, comprised of four alloys (nickel-titanium, 316L stainless steel, platinum-iridium, and tin-silver solder) and Dacron (PET) fibers, has been approved for use in the US for about two decades. However, little has been published on this implant's biomaterials performance, and as this implant gains interest in terms of in vivo performance, methods of implant post-retrieval storage also need to be assessed. This study investigated the electrochemical properties and ion release profile of Essure® during storage in phosphate buffered saline (PBS), 10 mM H2O2/PBS, a simulated inflammatory solution, and 10% neutral buffered formalin (NBF) to investigate the corrosion behavior and metal ion release. First, a galvanic test method was used to measure the galvanic interactions between alloys within the device. Second, an ion-release study over 107 days was performed. Ions were measured using inductively-coupled plasma mass spectrometry and the implants were assessed using digital optical microscopy, scanning electron microscopy, and energy dispersive x-ray spectrometry. The tin-silver (SnAg) solder continuously corroded in PBS and H2O2/PBS. In the presence of H2O2, nickel and titanium ions were released from the nickel-titanium (NiTi) coil, whereas release of these ions was minimal in PBS alone. Overall, corrosion of the SnAg solder, which holds the NiTi and 316L SS together, was significant in both PBS and H2O2/PBS and may result in loss of connection of the NiTi and 316L stainless steel portions of the implant. Storage in NBF exhibited very low corrosion rates for all alloys and low levels of ion release were observed indicating that formalin storage minimally affects the implant's corrosion status. STATEMENT OF SIGNIFICANCE: The Essure® device is an FDA premarket-approved female permanent sterilization device containing four different metal alloys and poly(ethylene terephthalate) polymer fibers. Significant concerns related to this device have been raised by the FDA since its introduction in 2002. This study is the first published in vitro work to specifically assess the corrosion mechanisms in this multi-alloy device and the role of different solution environments, including formalin storage, inorganic physiological saline and a simulated inflammatory condition. Significant evidence of corrosion of the tin-silver solder is documented, the release of Ni and Ti under simulated inflammatory conditions, and the relative inertness of storage of these implants in neutral buffered saline is presented. The tin-silver corrosion corroborates recent clinical evidence of tin corrosion products in tissues adjacent to these devices in vivo.

Long-term fretting corrosion performance of modular head-neck junctions with self-reinforced composite gaskets from PEEK and UHMWPE.

Soft gasket-like polymer films may provide multiple advantages in inhibiting fretting corrosion between metal-hard surfaces in total joint implants. Self-reinforced composites (SRC's) made from either poly(ether ether ketone), SRC-PEEK, or ultra high molecular weight polyethylene, SRC-PE, were fabricated and tested to investigate their ability to limit or prevent mechanically assisted corrosion in modular taper devices. Hot compaction was used to create nominally 100 µm thick unidirectional composite gaskets. These gaskets were placed on the trunnions of modular head-neck tapers and seated with 4000 N. One million cycle potentiostatic fretting corrosion tests (3000 N, R = 0.1, 15 Hz, -0.05 V) were employed to assess the ability of these SRCs to reduce or prevent fretting corrosion damage in the modular taper junction. Fretting currents and head-neck micromotion were evaluated. The results of testing, along with pull-off tests and optical and scanning electron microscopic analysis showed that SRC gaskets reduced or eliminated fretting corrosion currents, with the SRC-PEEK performing better than the SRC-PE. Fretting currents were low for SRC's compared to metal-metal tapers. No wear through of the gaskets was noted and minimal wear damage was seen in the SRC-PEEK gaskets. SRC-PE gaskets demonstrated greater deformation and damage compared to the SRC-PEEK gaskets. Pull-off loads for the SRC-PEEK were higher than SRC-PE and not statistically different than the control metal-metal junctions. There was evidence of fatigue cracks forming at the high stress concentration junctions for the SRC-PEEK at the thread form corners of the trunnion, but no loss of integrity was observed. SRC-PEEK gaskets show promise as a method to eliminate modular taper fretting corrosion.

Interfacial compliance, energy dissipation, frequency effects, and long-term fretting corrosion performance of Ti-6Al-4V/CoCrMo interfaces.

Fretting corrosion in modular orthopedic implants is a well-documented process that may be associated with adverse local tissue reactions, pain, and revisions. Engineering modular junction interfaces to withstand applied fretting motion without surface abrasion could prevent implant degradation and surface damage. Previous work on geometrically modified Ti-6Al-4V/CoCrMo interfaces with increased compliance showed reduced fretting currents and surface damage during short term, variable-load in vitro testing. This study assesses the same interfaces under long-term conditions using an in vitro pin-on-disk fretting corrosion test apparatus. Preliminary variable-load frequency testing of typical control pin geometries showed a frequency-dependent current response, with underlying contact conditions of metal-metal interfaces that remained unchanged. One-million-cycle testing showed diminished fretting currents in all groups by 5 × 105  cycles, but consistently lower currents in the high-compliance group. Corresponding fretting currents and work of fretting measurements of high-compliance pins confirmed that minimal fretting was experienced at the interface, with elastic bending of the pin accounting for almost all applied displacement. Debris generated during testing were composed of titanium and chromium oxides, small amounts of cobalt and molybdenum oxides, and sodium and phosphate originating from the surrounding test solution. Post-test analyses of sample surfaces revealed substantially more surface damage on CoCrMo disks than Ti-6Al-4V pins, thought to be a result of adhesive wear of mixed oxide debris on the pin and abrasion of the disk by the oxide debris layer. Surface damage to high-compliance pins suggests some abrasion is unavoidable with geometric modifications.

The effect of hypochlorous acid on the tribocorrosion of CoCrMo/Ti-6Al-4V bearing couples.

Mechanically assisted corrosion (MAC) of metallic orthopedic alloys is a consequence of the use of modular devices where opposing metal surfaces are tightly mated and loaded at the taper junction. MAC processes are affected by material surface characteristics and local solution chemistry. During inflammation, active immune cells may generate reactive oxygen species (such as hypochlorous acid [HOCl]) adjacent to surfaces undergoing micromotion, which may affect the tribocorrosion behavior of an implanted device. This study investigated the fretting current response of CoCrMo/Ti-6Al-4 V couples in a pin-on-disk apparatus utilizing HOCl solutions as a proxy for a severe inflammatory environment. Testing in 1 and 5 mM HOCl solutions were shown to generate a threefold and fivefold increase (p < 0.01), respectively, in fretting currents over pH 7.4 phosphate-buffered saline control conditions. Fretting currents were shown to be dependent on the energy dissipated during fretting and the concentration of HOCl where the currents within a single HOCl concentration were linearly dependent of energy dissipated, but different HOCl levels shifted (increased and then decreased) fretting currents with concentration. Fretting currents, governed by regrowth of an abraded oxide film, were affected by the oxidative power of the solution, which caused positive shifts in open circuit potential and likely resulted in a thicker oxide for 1 mM and 5 mM and fell with 30 mM. Small amounts of HOCl release within a joint may result in increased release of tribocorrosion products such as oxide particles.

Cytotoxic effect of galvanically coupled magnesium-titanium particles on Escherichia coli.

Orthopedic device-related infections (ODRIs) are difficult to control due to microbial biofilm formation and associated with high-level resistance to conventional antibiotics. In many cases, the only treatment option for ODRI is explantation. Previous studies have shown that application of cathodic potentials at the metal surface can eradicate biofilms, and Mg and Mg-Ti particles have the same effect as cathodic potentials. This study investigated the effects of Mg and Mg-Ti particles on established biofilms and planktonic cells E. coli. Bacterial cultures with developed biofilms or planktonic cells were treated with Mg or Mg-Ti particles, and the viability were assessed using flow cytometry or visual assessment methods (i.e., observation from SEM images and opacity of the solution). It was found that viability of biofilms treated with 16.67 mg/ml of Mg was 2.8 ± 0.96% at the end of 6-hr killing compared to untreated controls. This extent of killing was more significant compared to 24-hr grown biofilms treated with ofloxacin, an antibiotic known to be effective against these bacteria. Biofilms treated with 50 and 100 µg/ml of ofloxacin had 62 ± 4.6% and 52 ± 19.3% survival, respectively, where ofloxacin at these concentrations is known to kill planktonic counterparts very effectively. Inhibition zone tests revealed that biofilms within 2 mm of Mg or Mg-Ti particle clusters were effectively killed. These results demonstrated the potential of Mg or Mg-Ti particles in killing microbial biofilms and potential for controlling ODRI.

Nontribological corrosion modes dominate wrought CoCrMo acetabular taper corrosion: A retrieval study.

Corrosion of modular metal-on-metal acetabular tapers in total hip arthroplasty (THA) systems is often attributed to mechanically driven processes. Recent findings suggest that mechanically assisted crevice corrosion (MACC) might not be the dominant cause of corrosion in shell-liner tapers. This study aims to document and present the corrosion modes observed in metal-metal acetabular liners. Twenty-one retrieved wrought CoCrMo liners were examined using digital optical microscopy (DOM), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Corrosion-related damage was documented in nonengagement taper regions, outside of direct taper contact. Within engagement regions, nonmechanically driven corrosion features (pitting, intergranular corrosion) were observed adjacent to fretting and material transfer, which rely on mechanical contact; corrosion independent of MACC was observed even in contact regions. Corrosion types observed included intergranular corrosion (IGC), pitting attack, phase boundary dissolution, all both outside and inside of taper junctions, and MACC within contact regions of the taper. Typical fretting scars associated with MACC were mostly absent, and were not always associated with corrosion damage where present. Finally, hard phase particles (Mo-Si-O) released from the wrought CoCrMo microstructure had redeposited within regions with material loss. Acetabular taper corrosion modes differ significantly from those in head-neck tapers and are dominated by electrochemically driven processes, not mechanical processes, as indicated by corrosion in noncontact regions. With greater prevalence of dual mobility hip implants, acetabular taper corrosion processes must be understood in order to limit their impact on device performance.

Electrocautery-induced molten metal particle generation from total joint replacements: Morphology and chemistry.

Electrosurgical techniques are used during surgery to cauterize, and their damaging effects have primarily been documented in terms of tissue necrosis, charring, and localized heat accumulation. Metallic implants as well as the surgical blade can experience incidental electrosurgical current arcing that results in the generation and transfer of melted metallic particles. This work examines the composition, particle size distribution, and chemical state of the melted alloy surfaces and particles produced in vitro. Using scanning electron microscopy and energy dispersive spectroscopy, a flash-melting particle generation phenomenon between source 304 SSL blades and polished cobalt-chromium-molybdenum (CoCrMo) and titanium-6-aluminum-4-vandaium (Ti6Al4V) surfaces was documented where 304 SSL mixed heterogeneously with the CoCrMo and Ti6Al4V ejecting "splatter" particles from the cautery site. The spherical micron-sized particles were embedded with sub-micron-sized particles with 42% of the total sample population measuring between 0.25 and 0.35 µm in diameter. CoCrMo-304 SSL particles were principally made of high concentrations of iron, oxygen, and nickel with embedded sub-micron-sized particles containing oxygen, chromium, and cobalt with lower concentrations of iron and molybdenum. Ti6Al4V-304 SSL interactions resulted in similar micron-sized particles made up of high concentrations of iron, nickel, and chromium with embedded sub-micron-sized particles containing titanium, oxygen, and small amounts of aluminum. X-ray photoelectron spectroscopy of damaged CoCrMo surfaces confirmed the presence of chromium (VI) following dry electrocautery contact in coagulation mode. The structural effects of electrocautery-induced damage are becoming visible in retrieval analysis, but the long-term physiological implications during the lifetime of the implant from this damage mode have yet to be defined.

Self-reinforced poly(ether ether ketone) and polyethylene composite gaskets for prevention of mechanically-assisted corrosion in modular taper junctions: Seating, micromotion and short-term fretting corrosion.

Mechanically-assisted crevice corrosion (MACC) is a phenomenon known to cause complications in modular orthopedic implants, particularly at metal-metal taper junctions. Previous studies of the properties and corrosion performance of an interfacial polymeric self-reinforced composite (SRC) gaskets have shown its capability as a high-strength, insulating barrier against oxide abrasion and metal degradation of metal-metal (or metal-hard) contacts in MACC conditions. This study characterizes the short-term tribocorrosion performance of poly (ether ether ketone) SRCs (SRC-PEEK) and polyethylene SRC (SRC-PE) films under in vitro test conditions for head-neck modular junction designs in hip replacement devices. SRC films composed of SRC-PEEK and SRC-PE were seated between 9/10 femoral head bores and stem tapers as thin interfacial gaskets and tested against metal-metal controls under short-term cyclic loading conditions in a custom in vitro test setup. Head-neck seating mechanics were measured, followed by incremental cyclic fretting corrosion testing with monitoring of fretting current, force, and relative micromotion between head and neck components during cyclic loading. SRC-PEEK tapers had a seating subsidence that was approximately three times that of the SRC-PE tapers and nine times that of controls. SRC-PE tapers, likely due to low friction, partially failed to lock during seating resulting in a pushing up of the head on the taper. Average fretting currents were significantly lower for both SRC groups (less than 0.3 µA at 4000 N) compared to control tapers experiencing fretting corrosion currents between 1.7 µA and 32 µA, (p < 0.05). SRC-PEEK gaskets exhibited similar subsidence and micromotion performance as controls while SRC-PE tapers experienced over 240 µm of subsidence during seating and loading conditions. The SRC-PE low-friction properties likely caused insufficient taper locking, which may increase the risk of improper head seating or head disassociation. These results show that SRC-PEEK gaskets, unlike SRC-PE gaskets, can maintain adequate frictional locking at the taper junction and prevent the onset of MACC. SRC-PEEK gaskets improve the performance of modular taper junctions and could be considered as a potential solution to mitigate fretting corrosion.