Investigation on the Corrosion Resistance Properties of Cobalt-Chromium-Molybdenum Alloy Artificial Human Body Components with Robust Biomimetic Superhydrophobic and Slippery Surfaces Based on Laser Texturing.

Cobalt-chromium-molybdenum alloy is used as a material for artificial human body components such as artificial hip joint and artificial denture and is often affected by electrochemical corrosion in human body fluids and saliva, which leads to inflammatory reactions and damage to the surrounding tissues as well as loosening and failure of the body components themselves. Few studies have been conducted to prepare corrosion-resistant coatings on the surface of Co28Cr6Mo. In this study, we used laser texturing to process a bionic 3D micronanocomposite structure on the surface of Co28Cr6Mo and quickly prepared a superhydrophobic and slippery surface coating with excellent corrosion resistance using polydimethylsiloxane solution and silicone oil modification. This surface had ultralow surface adhesion and good robustness of durability and abrasion resistance, reducing bacterial colonization or tissue adhesion and solving the problem of the lack of stability of the superhydrophobic surface. Microgrid grooves and layered nanoparticles were structurally responsible for the variation in wettability. The formation mechanism and composition of the prepared coatings were further analyzed. Electrochemical corrosion experiments were conducted on the surface in simulating body fluid and saliva environments, which showed the enhanced corrosion resistance of the prepared surface in the human body. These findings can further develop the surface functional modification of Co28Cr6Mo, accelerating basic and applied research studies on artificial human components.

The Longest Known Follow-Up of Vitallium Mold Arthroplasty in China: A Case Report and Literature Review.

BACKGROUND: Before the advent of total hip arthroplasty, Vitallium mold arthroplasty had been widely performed. We present a case with a 42-year follow-up after Vitallium mold arthroplasty. To our knowledge, this case represents the longest known follow-up of Vitallium mold arthroplasty in China. CASE PRESENTATION: This was a 59-year-old male. He underwent Vitallium mold arthroplasty of the left hip 42 years ago because of osteonecrosis of the femoral head. He developed left hip pain 3 months ago and underwent total hip revision surgery. There was some clear synovial fluid in the hip joint. The mold was loosened entirely and taken out effortlessly. Gram-positive cocci could be observed occasionally in the synovial fluid smear, while the synovial fluid culture was negative. The inflammatory markers elevated perioperatively, and prophylactic cefuroxime and vancomycin were utilized successively. All elevated inflammatory markers fell since postoperative day 5, and there was no other sign of infection. The pain and function of the hip joint improved significantly after surgery. CONCLUSIONS: Although Vitallium mold arthroplasty was inferior to total hip arthroplasty in survival rate and functional outcome, it did provide an excellent long-term function of the hip joint.

Has Wrought Cobalt-Chromium-Molybdenum Alloy Changed for the Worse Over Time?

BACKGROUND: Total hip arthroplasty (THA) failure due to tribocorrosion of modular junctions and resulting adverse local tissue reactions to corrosion debris have seemingly increased over the past few decades. Recent studies have found that chemically-induced column damage seen on the inner head taper is enabled by banding in the alloy microstructure of wrought cobalt-chromium-molybdenum alloy femoral heads, and is associated with more material loss than other tribocorrosion processes. It is unclear if alloy banding represents a recent phenomenon. The purpose of this study was to examine THAs implanted in the 1990s, 2000s, and 2010s to determine if alloy microstructure and implant susceptibility to severe damage has increased over time. METHODS: Five hundred and forty-five modular heads were assessed for damage severity and grouped based on decade of implantation to serve as a proxy measure for manufacturing date. A subset of heads (n = 120) was then processed for metallographic analysis to visualize alloy banding. RESULTS: We found that damage score distribution was consistent over the time periods, but the incidence of column damage significantly increased between the 1990s and 2000s. Banding also increased from the 1990s to 2000s, but both column damage and banding levels appear to recover slightly in the 2010s. CONCLUSION: Banding, which provides preferential corrosion sites enabling column damage, has increased over the last 3 decades. No difference between manufacturers was seen, which may be explained by shared suppliers of bar stock material. These findings are important as banding can be avoidable, reducing the risk of severe column damage to THA modular junctions and failure due to adverse local tissue reactions.

Hip implant modular junction: The role of CoCrMo alloy microstructure on fretting-corrosion.

Cobalt-chromium-molybdenum (CoCrMo) alloy is one of the most used metals in total hip replacement (THR) due to the alloy's superior corrosion qualities and biocompatibility. Over time these prostheses may undergo wear and corrosion processes in a synergistic process known as tribocorrosion. Implant retrieval studies have shown that damage patterns on THR modular junction surfaces indicating specifically in vivo fretting-corrosion to take place. To date, there have been no studies on the fretting-corrosion behaviors of CoCrMo alloy under the consideration of specific microstructural features. A custom-built flat-on-flat fretting-corrosion setup was utilized to test the synergistic tribocorrosion behavior of fretting-corrosion. The difference in microstructure was generated through the cutting orientations of the transverse and the longitudinal direction of the bar stock material, where the longitudinal cut exhibits a characteristic banded microstructure (banded group) and the transverse cut a homogenous microstructure (unbanded group). A three-electrode system was employed to monitor the induced currents. Two different types of electrolytes were used in the current study: 1. Bovine calf serum (BCS-30 g/L protein) (normal conditions) 2. BCS with Lipopolysaccharide (LPS, 0.15 µg/ml) (simulated infectious conditions). In the free potential mode, banded samples showed an increased potential compared to the unbanded samples. In potentiostatic conditions, the banded group also exhibited a higher induced current in both electrolyte environments, indicating more corrosion loss. Both Nyquist and Bode plots showed both orientations of metal becoming more corrosion resistant post-fretting when compared to pre-fretting data. The longitudinal group at OCP demonstrated a unique shape of the fretting-loop, which might be related to tribochemical reactions. Based on the mechanical, electrochemical, and surface characterization data, the transverse group (unbanded) microstructures demonstrates a higher resistance to fretting-corrosion damage.

Synchrotron-based characterization of arthroprosthetic CoCrMo particles in human bone marrow.

Particles released from cobalt-chromium-molybdenum (CoCrMo) alloys are considered common elicitors of chronic inflammatory adverse effects. There is a lack of data demonstrating particle numbers, size distribution and elemental composition of bone marrow resident particles which would allow for implementation of clinically relevant test strategies in bone marrow models at different degrees of exposure. The aim of this study was to investigate metal particle exposure in human periprosthetic bone marrow of three types of arthroplasty implants. Periprosthetic bone marrow sections from eight patients exposed to CoCrMo particles were analyzed via spatially resolved and synchrotron-based nanoscopic X-ray fluorescence imaging. These analyses revealed lognormal particle size distribution patterns predominantly towards the nanoscale. Analyses of particle numbers and normalization to bone marrow volume and bone marrow cell number indicated particle concentrations of up to 1 × 1011 particles/ml bone marrow or 2 × 104 particles/bone marrow cell, respectively. Analyses of elemental ratios of CoCrMo particles showed that particularly the particles' Co content depends on particle size. The obtained data point towards Co release from arthroprosthetic particles in the course of dealloying and degradation processes of larger particles within periprosthetic bone marrow. This is the first study providing data based on metal particle analyses to be used for future in vitro and in vivo studies of possible toxic effects in human bone marrow following exposure to arthroprosthetic CoCrMo particles of different concentration, size, and elemental composition. Graphical abstract.

In-Vitro Cell-Induced Corrosion by Macrophages on Cobalt-Chromium-Molybdenum Alloy.

BACKGROUND: Patients have received cobalt-chromium-molybdenum (CoCrMo) implants for their joint replacement for decades. There have been reports of inflammatory cell-induced corrosion (ICIC) of these implants from retrieval studies. The goal of this study is to see if we could recreate ICIC in vitro and whether electrocautery damage to alloy surfaces may hasten this process. METHODS: Murine macrophages were cultured on CoCr disks with and without damage from a monopolar electrocautery. Culture medium was replaced every 12 hours and supernatant was collected every 4 days. After 30 days, cells were removed, counted, and digested. The metal concentrations in the supernatant and within cells were assessed using inductively coupled plasma spectrometry for comparison. RESULTS: The Co supernatant concentration was higher in the undamaged disks with activated macrophages. Higher concentrations of Co and Mo were found in the supernatant of the undamaged disks vs the electrocautery (EC) corrosion damaged disks. There was a significantly higher intracellular Co and Mo concentration with activated cells on CoCrMo disks vs the control group and no difference compared to EC damaged disk group. Scanning electron microscopy displayed microscopic pitting on the surfaces exposed to macrophages without EC damage. CONCLUSION: We found that macrophages could reproduce findings of ICIC pits on the surface of CoCrMo alloy and that the addition of EC damage to the surface did not increase the process. The clinical significance of these findings should be further investigated to determine if this could explain a small number of poor total knee arthroplasty reported outcomes.

Binding stability of peptides to Co-Cr-Mo alloy affects proliferation and differentiation of osteoblast.

Cobalt-chromium-molybdenum (CCM) alloys possess high corrosion-resistant properties as well as good mechanical properties. Hence, the alloys are employed in medical implants such as artificial knee and hip joints, coronary stents, and removable partial dentures. To improve the biocompatibility of CCM alloys, we reported that CCM-binding peptide (CBP) linked to cell-adhesive motif Arg-Gly-Asp (RGD) improved the attachment of endothelial cells on CCM alloys. However, the stability of CBP adsorption on the alloy and its effect on osteoblast compatibility are still unclear. In this study, we evaluated the stabilization of the adsorption layer of CBP-RGD on CCM alloy surface and investigated the effect of CBP-RGD peptide on the proliferation and differentiation of the osteoblasts. CBP-RGD layer exhibited higher stabilization than the RGD adsorption layer for 7 days. In addition, the proliferation of osteoblast on CBP-RGD adsorbed alloy higher than that on RGD adsorbed alloy. Moreover, the calcification of cells cultured on the CBP-RGD adsorbed alloy was significantly higher than that of the cells on RGD adsorbed alloy. These findings indicate that the CBP binding was stable during the culture of osteoblasts on the CCM alloy.

Coating CoCrMo Alloy with Graphene Oxide and ε-Poly-L-Lysine Enhances Its Antibacterial and Antibiofilm Properties.

INTRODUCTION: With increases in implant infections, the search for antibacterial and biofilm coatings has become a new interest for orthopaedists and dentists. In recent years, graphene oxide (GO) has been extensively studied for its superior antibacterial properties. However, most of these studies have focused on solutions and there are few antibacterial studies on metal surfaces, especially the surfaces of cobalt-chromium-molybdenum (CoCrMo) alloys. ε-Poly-L-lysine (ε-PLL), as a novel food preservative, has a spectrum of antimicrobial activity; however, its antimicrobial activity after coating an implant surface is not clear. METHODS: In this study, for the first time, a two-step electrodeposition method was used to coat GO and ε-PLL on the surface of a CoCrMo alloy. Its antibacterial and antibiofilm properties against S. aureus and E. coli were then studied. RESULTS: The results show that the formation of bacteria and biofilms on the coating surface was significantly inhibited, GO and ε-PLL composite coatings had the best antibacterial and antibiofilm effects, followed by ε-PLL and GO coatings. In terms of classification, the coatings are anti-adhesive and contact-killing/inhibitory surfaces. In addition to oxidative stress, physical damage to GO and electrostatic osmosis of ε-PLL are the main antibacterial and antibiofilm mechanisms. DISCUSSION: This is the first study that GO and ε-PLL coatings were successfully prepared on the surface of CoCrMo alloy by electrodeposition. It provides a promising new approach to the problem of implant infection in orthopedics and stomatology.

CoCrMo-Nanoparticles induced peri-implant osteolysis by promoting osteoblast ferroptosis via regulating Nrf2-ARE signalling pathway.

OBJECTIVES: Aseptic loosening (AL) is the most common reason of total hip arthroplasty (THA) failure and revision surgery. Osteolysis, caused by wear particles released from implant surfaces, has a vital role in AL. Although previous studies suggest that wear particles always lead to osteoblast programmed death in the process of AL, the specific mechanism remains incompletely understood and osteoblast ferroptosis maybe a new mechanism of AL. MATERIALS AND METHODS: CoCrMo nanoparticles (CoNPs) were prepared to investigate the influence of ferroptosis in osteoblasts and calvaria resorption animal models. Periprosthetic osteolytic bone tissue was collected from patients who underwent AL after THA to verify osteoblast ferroptosis. RESULTS: Our study demonstrated that CoNPs induced significant ferroptosis in osteoblasts and particles induced osteolysis (PIO) animal models. Blocking ferroptosis with specific inhibitor Ferrostatin-1 dramatically reduced particle-induced ferroptosis in vitro. Moreover, in osteoblasts, CoNPs significantly downregulated the expression of Nrf2 (nuclear factor erythroid 2-related factor 2), a core element in the antioxidant response. The overexpression of Nrf2 by siKeap1 or Nrf2 activator Oltipraz obviously upregulated antioxidant response elements (AREs) and suppressed ferroptosis in osteoblasts. Furthermore, in PIO animal models, the combined utilization of Ferrostatin-1 and Oltipraz dramatically ameliorated ferroptosis and the severity of osteolysis. CONCLUSIONS: These results indicate that CoNPs promote osteoblast ferroptosis by regulating the Nrf2-ARE signalling pathway, which suggests a new mechanism underlying PIO and represents a potential therapeutic approach for AL.

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.

Implant-derived CoCrMo alloy nanoparticle disrupts DNA replication dynamics in neuronal cells.

The complexity of cobalt-chromium-molybdenum (CoCrMo) nanoparticles generated from the hip modular taper interfaces resulted in inconclusive outcomes on the level of toxicity in orthopedic patients. We used a hip simulator to generate physiologically relevant CoCrMo degradation products (DPs) to demonstrate the variation in the level of toxicity in neurons in comparison to processed degradation products (PDPs). The study outcomes indicate that DP induces a higher level of DNA damage in the form of double- and single-stranded DNA breaks and alkaline labile DNA adducts versus PDPs. The scientific advancements of this study are the following: (i) how DPs mimic more closely to the implant debris from hip implants in terms of bioactivity, (ii) how hip implant debris causes local and systemic issues, and (iii) methods to augment the biologic impact of implant debris. We discovered that DP is bioactive compared with PDP, and this should be considered in the toxicity evaluation related to implants. • The physicochemical characteristics of the CoCrMo is a major factor to consider for implant-related cytotoxicity or genotoxicity experimental design. • Elevated levels of intracellular ROS induced by the physiologically relevant wear particle are detrimental to the neuronal cells. • The DP can induce variation in DNA replication dynamics compared to PDP.

Effect of surface mechanical attrition treatment on the microstructure of cobalt-chromium-molybdenum biomedical alloy.

This research work describes the impact of the surface mechanical attrition treatment (SMAT) on the microstructure of cobalt-chromium-molybdenum (CoCrMo), a biomedical alloy commonly used for orthopedic applications. This surface treatment induces crystalline phases transformations characterized by X-ray diffraction (XRD) and selected area electron diffraction (SAED). The corresponding structural changes are observed from cross-section images obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the SMAT process induces the martensitic transformation of the CoCrMo alloy (from γ-fcc phase to ε-hcp phase) related to an important grain refinement due to twinning and sliding.

No clinical difference between TiN-coated versus uncoated cementless CoCrMo mobile-bearing total knee arthroplasty; 10-year follow-up of a randomized controlled trial.

PURPOSE: Improvement of biomechanical properties of cobalt-chromium-molybdenum (CoCrMo) implant surface and reduction of adhesive wear is achieved by titanium-nitride (TiN) coating in vitro. Less pain, higher postoperative outcome scores and a lower revision rate after TKA with a TiN-coated CoCrMo TKA compared with uncoated CoCrMo TKA after 10-year follow-up was hypothesized. METHODS: In a double-blinded RCT, 101 patients received a cementless mobile-bearing CoCrMo TKA, either TiN-coated or uncoated. The primary outcome measure was the visual analogue scale (VAS) score for pain and secondary outcome measures were the Knee Society Score (KSS), Oxford Knee Score (OKS), revision rate and adverse events. Patients were assessed at 6 weeks, 6 months, 1 year, 5 years and 10 years, postoperatively. RESULTS: 68 patients (67%) were available for 10-year follow-up. No difference was found in any of the assessed outcome measures with a mean decrease in VAS score (31.6 ± 22.9) and a mean increase in OKS (10.9 ± 8.4), KSS (29.3 ± 31.4), KSSK (26.4 ± 18.2) and KSSF (4.1 ± 22.9). Overall revision rate was 7% (coated 6% vs uncoated 8%) without additional revision procedures between 5 and 10-year follow-up. CONCLUSIONS: The in vitro potential benefits of TiN coating did not result in better clinical outcome when compared to an uncoated cementless TKA. Pain, functional outcome and revision rates were comparable after 10-year follow-up. TiN-coated cementless TKA provides comparable good long-term results, similar to uncoated cementless CoCrMo TKA. LEVEL OF EVIDENCE: Level 1, Therapeutic Study NETHERLANDS TRIAL REGISTER: NL2887/NTR3033.

Cytotoxic effects of dental prosthesis grinding dust on RAW264.7 cells.

Respiratory diseases, including pulmonary fibrosis, silicosis, and allergic pneumonia, can be caused by long-term exposure to dental prosthesis grinding dust. The extent of the toxicity and pathogenicity of exposure to PMMA dust, Vitallium dust, and dentin porcelain dust differs. The dust from grinding dental prosthesis made of these three materials was characterized in terms of morphology, particle size, and elemental composition. The adverse effects of different concentrations of grinding dust (50, 150, 300, 450, and 600 µg ml-l) on RAW264.7 macrophages were evaluated, including changes in cell morphology and the production of lactate dehydrogenase (LDH) and reactive oxygen species (ROS). The dust particles released by grinding dental prosthesis made of these materials had different morphologies, particle sizes, and elemental compositions. They also induced varying degrees of cytotoxicity in RAW264.7 macrophages. A possible cytotoxicity mechanism is the induction of lipid peroxidation and plasma membrane damage as the dust particles penetrate cells. Therefore, clinicians who regularly work with these materials should wear the appropriate personal protection equipment to minimize exposure and reduce the health risks caused by these particulates.

In vitro effects of macrophages on orthopaedic implant alloys and local release of metallic alloy components.

AIMS: This study aimed to determine if macrophages can attach and directly affect the oxide layers of 316L stainless steel, titanium alloy (Ti6Al4V), and cobalt-chromium-molybdenum alloy (CoCrMo) by releasing components of these alloys. METHODS: Murine peritoneal macrophages were cultured and placed on stainless steel, CoCrMo, and Ti6Al4V discs into a 96-well plate. Cells were activated with interferon gamma and lipopolysaccharide. Macrophages on stainless steel discs produced significantly more nitric oxide (NO) compared to their control counterparts after eight to ten days and remained elevated for the duration of the experiment. RESULTS: On stainless steel, both nonactivated and activated cell groups were shown to have a significant increase in metal ion release for Cr, Fe, and Ni (p < 0.001, p = 0.002, and p = 0.020 respectively) compared with medium only and showed macrophage-sized corrosive pits on the stainless steel surface. On titanium alloy discs there was a significant increase in aluminum (p < 0.001) among all groups compared with medium only. CONCLUSION: These results indicated that macrophages were able to attach to and affect the oxide surface of stainless steel and titanium alloy discs. Cite this article: Bone Joint J 2020;102-B(7 Supple B):116-121.

A metallic biomaterial tribocorrosion model linking fretting mechanics, currents, and potentials: Model development and experimental comparison.

Mechanically assisted crevice corrosion may disrupt passive oxide films on medical alloys and lead to rapid repassivation reactions which generate corrosion currents and shifts in electrode potential due to the non-equilibrium nature of the reactions and the transient unbalancing of anodic and cathodic reactions. This study presents a theoretical approach to predict currents and voltages over time utilizing the concepts of heredity integrals, area-dependent surface impedance, contact mechanics and the high field physics of oxide repassivation. Two heredity integrals are presented relating, first, the sliding mechanics and oxide film repassivation physics to the current, and second, relating the electrode potential to the current using impedance concepts. Current-potential-time responses to controlled fretting conditions were measured across a fretting frequency from 0.2 to 10 Hz and compared to theoretical results. The coupled integrals were shown to predict the overall current-potential-time behavior for CoCrMo alloy surfaces under several controlled fretting corrosion conditions (loads, sliding speeds, etc.) with a high degree of similarity. These models can be adapted to numerical analyses of tribocorrosion to predict performance.

Fretting corrosion of Si3 N4 vs CoCrMo femoral heads on Ti-6Al-V trunnions.

Fretting corrosion at the head-neck taper junction was compared between silicon nitride (Si3 N4 ) and commercially available cobalt chrome (CoCrMo) femoral heads on titanium (Ti-6Al-4V) trunnions. An electrochemical setup was used to capture the fretting currents (characterized by oxide abrasion and repassivation) during cyclic loading. Onset load, pull-off force (disassembly load), short term and long term (1 million cycles) fretting currents were used to compare the fretting corrosion performance between the test group (Si3 N4 /Ti-6Al-4V) and the control group (CoCrMo/Ti-6Al-4V). Incremental cyclic fretting corrosion tests showed that the Si3 N4 /Ti-6Al-4V combination had statistically lower (P < .05) average fretting current of 0.189 µA (SD = 0.114 µA) compared to 0.685 µA (SD = 0.630 µA) for CoCrMo/Ti-6Al-4V for cyclic load of 3200 N. Similarly, for the one million cycle fretting corrosion tests, the Si3 N4 /Ti-6Al-4V couples had statistically lower (P < .05) average current (0.048 µA, SD = 0.025 µA) vs CoCrMo/Ti-6Al-4V couples (0.366 µA, SD = 0.143 µA). The Si3 N4 heads also had higher onset loads (P < .05) for fretting (vs CoCrMo, 2200 N vs 1740 N) indicating a difference in surface contact mechanics between the two groups. Scanning electron microscopy with energy dispersive spectroscopy confirmed material transfer from the trunnions to the heads for both groups tested, and from head to trunnion for the CoCrMo heads. Minimal Si3 N4 transfer was noted. The electrochemical, mechanical, and microscopic inspection data supported the hypothesis that Si3 N4 /Ti-6Al-4Vcombination had better fretting corrosion performance compared to CoCrMo/Ti-6Al-4V.

CoCrMo metal release in metal-on-highly crosslinked polyethylene hip implants.

Increasing cases of adverse local tissue reactions (ALTRs) associated with metal release have been observed in patients with metal-on-highly crosslinked polyethylene (MoP) hip implants, the most common design in total hip replacements. Studies have demonstrated the metal release from fretting corrosion at the head-neck junction, but rarely investigated tribocorrosion associated metal release at articulating surfaces in MoP hip implants. The objective of this study is to investigate both tribocorrosion at the articulating surfaces and fretting corrosion at the head-neck junction in CoCrMo femoral heads, as well as their association with metal species released in periprosthetic tissues and body fluids in MoP hip systems. Twenty-three patients with ALTRs associated with MoP implants were included. Systematic analyses were performed on the wear damage in articulation, corrosion at the head-neck junction and their correlation with degradation products observed in synovial fluid, periprosthetic tissues, and serum. Results showed that tribocorrosion at the articulating surfaces contributed to the elevated concentration of both Co and Cr ions in serum, while fretting corrosion at the head-neck junction mainly released Co ions to serum. Both tribocorrosion at the articulating surfaces and fretting corrosion at the head-neck junction released particles rich in chromium and phosphate, the dominant particles found in synovial fluids and tissues. This study provides strong evidence that tribocorrosion at the articulating surfaces in MoP hip implants could result in significant metal release. This information should be taken into account when studying the mechanisms of ALTRs and developing strategies of preventing metal release in total hip replacements.

Effect of heat treatment on the anisotropic microstructural and mechanical properties of Co-Cr-Mo alloys produced by selective laser melting.

The purpose of this study was to evaluate the effect of heat treatment on the anisotropy of the microstructure and mechanical properties of cobalt-chromium-molybdenum (Co-Cr-Mo) alloys fabricated by selective laser melting (SLM). Dumbbell samples were fabricated with the axes deviating from the build direction by 0° (0°-sample), 45° (45°-sample), or 90° (90°-sample) and were subjected to heat treatment at various temperatures (750, 900, 1050, or 1150 °C) for 6 h. In samples heat-treated at 750, 900, and 1050 °C, the microstructures exhibited columnar grains with a <001> fiber texture along the build direction, the same as in the as-built state. The mechanical properties showed anisotropy; the 0.2% offset yield strengths (YS) of the 0°-samples were lower than those of the 90°-samples, and the elongations of the 0°-samples were significantly higher than those of the 45°- and 90°-samples. By contrast, in samples heated to 1150 °C for 6 h, the anisotropic columnar grains completely disappeared, and equiaxed grains with random orientations were found in all samples, indicating that recrystallization had occurred. Moreover, the specific microstructures and texture generated during SLM disappeared. Regarding tensile properties, the initially strong anisotropy exhibited by the as-SLM samples was significantly reduced. Thus, heat treatment at the recrystallization temperature produced uniform equiaxed grains with random texture, which contributed to reducing the mechanical anisotropy of the SLMed Co-Cr-Mo alloys.

Favorable modulation of osteoblast cellular activity on Zr-modified Co-Cr-Mo alloy: The significant impact of zirconium on cell-substrate interactions.

Cobalt-chromium-molybdenum alloys exhibit good mechanical properties (yield strength: ~530 MPa, ultimate tensile strength: ~1114 MPa, elongation-to-failure: ~47.3%, and modulus: ~227 GPa) and corrosion resistance. In recent years, from the perspective of osseointegration, they are considered to be lower in rank in comparison to the widely used titanium alloys. We elucidate here the significant and favorable modulation of cellular activity of Zr-modified Co-Cr-Mo alloys. The average grain size of Co-Cr-Mo alloy samples with and without Zr was 104 ± 27 and ~53 ± 11 µm, respectively. The determining role of small addition of Zr (0.04 wt. %) to the Co-Cr-Mo alloys in favorable modulation of cellular activity was accomplished by combining cellular biology and materials science and engineering. Experiments on the influence of Zr addition to Co-Cr-Mo alloys clearly demonstrated that the cell adhesion, spread and cell-substrate interactions were enhanced in the presence of Zr. The spread/growth rate of cells was ~120% on the Co-Cr-Mo alloy and 190% per day on the Co-Cr-Mo-Zr alloy. While the % area covered by the cells increased from ~5.1 to ~33.6% on Co-Cr-Mo alloy and ~19.2 to ~47.8% on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Similarly, the cell density increased from ~1354 to ~3424 cells/cm2 on Co-Cr-Mo alloy and ~3583 to ~7804 cells/cm2 on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Additionally, stronger vinculin focal adhesion contact and signals associated with actin stress fibers together with extracellular matrix protein, fibronectin, were noted.