Influence of Proteins and Building Direction on the Corrosion and Tribocorrosion of CoCrMo Fabricated by Laser Powder Bed Fusion.

Cobalt-chromium-molybdenum (CoCrMo) alloys are common wear-exposed biomedical alloys and are manufactured in multiple ways, increasingly using additive manufacturing processes such as laser powder bed fusion (LPBF). Here, we investigate the effect of proteins and the manufacturing process (wrought vs LPBF) and building orientation (LPBF-XY and XZ) on the corrosion, metal release, tribocorrosion, and surface oxide composition by means of electrochemical, mechanical, microscopic, diffractive, and spectroscopic methods. The study was conducted at pH 7.3 in 5 g/L NaCl and 5 mM 2-(N-morpholino) ethanesulfonic acid (MES) buffer, which was found to be necessary to avoid metal phosphate and metal-protein aggregate precipitation. The effect of 10 g/L bovine serum albumin (BSA) and 2.5 g/L fibrinogen (Fbn) was studied. BSA and Fbn strongly enhanced the release of Co, Cr, and Mo and slightly enhanced the corrosion (still in the passive domain) for all CoCrMo alloys and most for LPBF-XZ, followed by LPBF-XY and the wrought CoCrMo. BSA and Fbn, most pronounced when combined, significantly decreased the coefficient of friction due to lubrication, the wear track width and severity of the wear mechanism, and the tribocorrosion for all alloys, with no clear effect of the manufacturing type. The wear track area was significantly more oxidized than the area outside of the wear track. In the reference solution without proteins, a strong Mo oxidation in the wear track surface oxide was indicative of a pH decrease and cell separation of the anodic and cathodic areas. This effect was absent in the presence of the proteins.

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.

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.

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.

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.

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.

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.

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.

An assessment of biomedical CoCrMo alloy fabricated by direct metal laser sintering technique for implant applications.

CoCrMo alloys have been used for several decades in implantable devices due to their favourable mechanical properties, low wear rate in addition to good biocompatibility and high corrosion resistance. These alloys are conventionally produced via casting and/or forging route, however additive manufacturing techniques being recently employed in their fabrication. In this work, CoCrMo samples were produced by direct metal laser sintering additive manufacturing process. The microstructure and surface composition were examined employing scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The corrosion resistance was measured in 0.14 M sodium chloride solution and in phosphate buffered solution (PBS) both with and without addition of albumin at pH 7.4 and 37 °C. For this, potentiodynamic tests in addition to electrochemical impedance spectroscopy were employed. The studied CoCrMo alloy exhibits a good corrosion resistance in solutions tested being the highest in PBS solution without albumin addition. The XPS analysis showed that the passive film composition and its thickness are not modified by the adsorbed layer. Microstructural analysis revealed occurrence of strain-induced martensitic transformation.

CoCrMo alloys ions release behavior by TiNbN coating: an in vitro study.

The aim of the study was to show in vitro the greater inertness to the corrosion body fluid of TiNbN coating than the CoCrMo alloy substrate. The prosthetic component under study was a femoral component of total knee prosthesis in CoCrMo alloy coated in TiNbN with Physical Vapor Deposition technique immersed in static Hank's balanced salt solution (HBS) (pH = 6) for at least 34 months at a constant temperature of 37 °C. Another uncoated prosthetic component of CoCrMo alloy with the same type and size was left in static immersion in the same solution and for the same period of time. Scanning electron microscope (SEM) analysis was performed to investigate adhesion and proliferation at 24, 48, 72 h after seeding of 104 sub-confluents osteoblast-like cells (SaOS-2) cells on scaffold. The results of the study showed a reduction in the concentration of the metal ions released from the TiNbN-coated femoral component surface compared to the uncoated surface in the HBS solution. The overall reduction of the ions for the TiNbN-coated femoral component compared to the uncoated one was 80.1 ± 2%, 62.5% ± 8% and 48% ± 10% for Co, Cr, Mo, respectively (p < 0.01). SEM analysis confirmed the healthy state of the cells, the cellular adhesion and proliferation of SaOS-2 on the TiNbN-coated specimen. Although the results observed in vitro for the TiNbN coating are encouraging, clinical studies are certainly needed to be performed in order to understand how these positive findings can be translated in vivo and to determine the clinical benefit of TiNbN coating.

Negative influence of biofilm on CoCrMo corrosion.

Minimal studies exist investigating biofilm-induced corrosion of orthopaedic implants. This study investigates potential contributions of Pseudomonas aeruginosa and Staphylococcus aureus biofilms on corrosion resistance of CoCrMo under static and fretting conditions. Biofilms were cultured on CoCrMo coupons for either 4 weeks (static culture) or 6 days (fretting culture; pin-on-disk with a Ti6Al4V hemispherical tip pin). Morphology of biofilms and corrosion of coupon surfaces were analyzed via SEM. Open circuit potential and electrochemical impedance spectroscopy measurements were collected for corrosion performance evaluation. Results showed no visible corrosion on coupon surfaces in static culture, which suggests these biofilms alone do not induce severe corrosion under the conditions of this study. However, electrochemical data showed biofilm presence lowered coupon electrochemical impedance in static and fretting cultures, suggesting resistive and capacitive characteristics of the metal oxide-biofilm-media interface were altered. Under fretting, the P. aeruginosa group exhibited a distinct damage morphology and Co:Cr:Mo ratio within the wear scar when compared with S. aureus and the bacteria-free control. These differences suggest the presence of P. aeruginosa biofilms may negatively impact corrosion resistance at the fretting interface. Taken together these results demonstrate biofilms can contribute to implant corrosion by influencing the electrochemical impedance of implant metal surfaces.

Tribocorrosion of a CoCrMo alloy sliding against articular cartilage and the impact of metal ion release on chondrocytes.

Partial knee replacement and hemiarthroplasty are some of the orthopedic procedures resulting in a metal on cartilage interface. As metal implant material, CoCrMo based alloys are commonly used. The aim of the present study is to assess the role of biotribocorrosion on the CoCrMo-cartilage interface with an emphasis on metal release during sliding contact. The biotribocorrosion experiments were performed under controlled electrochemical conditions using a floating cell with a three electrode set up coupled to a microtribometer. Throughout the experiment the coefficient of friction and the open circuit potential were monitored. Analyses of the electrolyte after the experiment show that metal release can occur during sliding contact of CoCrMo alloy against articular cartilage despite the extraordinary low coefficient of friction measured. Metal release is attributed to changes in passive layer caused at the onset of sliding. The released metal was found to be forming compounds with potential cytotoxicity. Since the presence of metal ions in the cartilage matrix can potentially lead to cell apoptosis, the metabolic activity of human osteoarthritic chondrocytes (2D-cultures) was investigated in the presence of phosphate buffered saline containing metal ions using XTT-assay. The experiments indicate that critical concentrations of Co ions lead to a significant decrease in chondrocyte metabolic activity. Therefore, biotribocorrosion is a mechanism that can occur in partial replacements and lead to chondrocyte apoptosis thus playing a role in the observed accelerated degradation of the remaining cartilage tissue after the mentioned orthopedic procedures. STATEMENT OF SIGNIFICANCE: Partial replacements provide an alternative to total joint replacements. This procedure is less invasive, allows a faster rehabilitation and provides a better function of the joint. However, the remaining native cartilage experiences accelerated degradation when in contact with metallic implant components. This work investigates the role of tribocorrosion at the metal-cartilage interface during sliding. Tribocorrosion is a degradation process that can alter significantly the wear rates experienced by metallic implants and lead to the release of metal ions and particles. The released metal can form compounds with potential cytotoxicity on cartilage tissue. The knowledge gained in this work will serve to understand the mechanisms behind the failure of partial replacements and develop future biomaterials with an enhanced lifetime.

Breakage of metal hip arthroplasty components: Retrieval and structural analysis.

BACKGROUND: Breakage of joint arthroplasty components are rare, yet during an implant retrieval program we found several cases. OBJECTIVE: In this study we examined the components to determine the causes and mechanisms of breakage of these implants. METHODS: From our collection of 849 retrievals we selected 682 cases with metal parts (503 hip, 79 knee arthroplasties) and identified fractured components: seven hip resurfacing implants, five total hip replacement stems, one monopolar femoral head, and one modular revision femoral stem from. Implants were examined using optical and scanning electron microscopy; metallographic sections were prepared and samples of periprosthetic tissues underwent microscopic examination. RESULTS: In the resurfacing components breakage occurred in small stems placed in the femoral neck due to necrosis of femoral heads, with no metal flaws detected. Fatigue breakage of femoral stems was caused by presence of material flaws in the CoCrMo alloy, and corrosion. The monopolar head failed in fatigue fracture mechanism, breakage was initiated in an undercut near the taper connection for femoral component. The modular stem from Ti alloy sustained fatigue fracture induced by corrosion caused by debris from previously revised stem; no material flaws were detected in this sample. In most cases periprosthetic tissues had a morphology typical for aseptic loosening. CONCLUSIONS: In our series failure was caused by material flaws, presence of stress raisers and localized corrosion. Our findings indicate that sharp edges and other features which can act as stress raisers should be avoided in newly designed implants. Corrosion induced fracture of the modular Ti stem indicates the need for a detailed debridement of periprosthetic tissues during revision arthroplasties.

Investigation of nano-sized debris released from CoCrMo secondary interfaces in total hip replacements: Digestion of the flakes.

The in vivo release of wear debris and corrosion products from the metallic interfaces of total hip replacements is associated with a wide spectrum of adverse body reactions and systemic manifestations. The origin of debris and the electrochemical conditions at the sites of material loss both play a role in determining the physicochemical characteristics of the particles, and thus influence their in vivo reactivity. Debris retrieved from revised CoCrMo tapers and cement-stem interfaces consists of heterogeneous flakes that comprise mechanically mixed metal particles, corrosion products and organic material. Detailed investigation of the size and composition of the metal debris contained within these composites requires the digestion of the flakes to release the small metal particles. Here, we compare alkaline and enzymatic digestion methods that both aim to fragment the flakes and reveal their smallest building blocks. The characterization of debris cleaned with both methods revealed crystalline Cr oxide nanoparticles and clusters. Comparison between the treatments showed that the alkaline method is more efficient in fragmenting the flakes and provided cleaner and generally smaller nanoparticles than exhibited in debris released with the enzymatic treatment. The provision of cleaner nanoparticles from the alkaline method also allows the physicochemical properties of the particles to be more clearly identified. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 424-434, 2019.

Electrochemical potential zone of viability on CoCrMo surfaces is affected by cell type: Macrophages under cathodic bias are more resistant to killing.

Electrochemical interactions at the cell-metal interface determine cell viability and influence behavior in response to different electrode potential conditions, specifically cathodic biases. Mechanically assisted crevice corrosion, for example, induces cathodic potentials and the associated electrochemical consequences of increased reduction reactions at the implant surface may affect cell viability in a manner that is different for various cell phenotypes. Monocyte macrophage-like U937 cells were cultured on cobalt-chromium-molybdenum (CoCrMo) metal surfaces in vitro for 24 h to assess cell behavior in response to sustained applied voltages. The electrochemical zone of viability for U937 cells polarized for 24 h in vitro was -1000 ≤ mV < +500, compared to -400 < mV < +500 for MC3T3-E1 preosteoblast-like cells cultured under the same conditions, likely as a result of intrinsic apoptosis. Voltages above +250 mV had a lethal effect on U937 cells that was similar to that seen previously for MC3T3-E1 cells on biased CoCrMo surfaces. It appears that cell phenotype directly influences behavior in response to cathodic electrochemical stimuli and that the monocyte macrophage-like cells are more resistant to cathodic potential stimuli than preosteoblasts. This may be due to a glutathione-based increased ability to quench reactive oxygen species and inflammatory-associated radicals hypothesized to be generated during reduction of oxygen. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 526-534, 2019.

miR-130b participates in wear particle-induced inflammation and osteolysis via FOXF2/NF-κB pathway.

OBJECTIVE: To reveal other miR-130b-mediated signaling pathway in the involvement of wear particle-induced inflammation and osteolysis. MATERIALS AND METHODS: Particle-induced osteolysis (PIO) mice model was established. Secretion levels of TNF-α, IL-1ß, IL-6, and IL-10 were measured by ELISA. miR-130b and forkhead box F2 (FOXF2) mRNA were detected by qRT-PCR. Protein levels of FOXF2, phosphorylation-p65 (p-p65), and p-IκB were observed by Western blot. Luciferase reporter assay was performed to confirm the regulation of miR-130b on FOXF2. RESULTS: Compared with normal mice, secretion levels of TNF-α, IL-1ß, and IL-6 in PIO mice were significantly up-regulated and IL-10 was significantly down-regulated; miR-130b and p-p65 expressions were up-regulated and FOXF2 expression was down-regulated. In addition, the trends of miR-130b, FOXF2, and p-p65 expressions in Co-Cr-Mo treated Raw264.7 cells were the same as that in PIO mice. After transfection with miR-130b inhibitor, secretion levels of TNF-α, IL-1ß, and IL-6 in Raw264.7 cells were significantly decreased and secretion level of IL-10 was significantly increased. We also proved FOXF2 was a target of miR-130b, and FOXF2 siRNA increased secretion levels of TNF-α, IL-1ß, and IL-6 and decreased secretion level of IL-10. Finally, we found nuclear factor-kappa B (NF-κB) inhibitor BAY 11-7082 further decreased secretion levels of TNF-α, IL-1ß, and IL-6 and increased IL-10 level. CONCLUSION: The role of miR-130b/FOXF2/NF-κB pathway in PIO was firstly revealed, which provided new targets for the treatment of periprosthetic osteolysis.

Differential toxicity of processed and non-processed states of CoCrMo degradation products generated from a hip simulator on neural cells.

Physico-chemical characteristics of the CoCrMo degradation products have played an important role in cytotoxicity and clinical complications on the orthopedic patients who have metal implants. Previous studies have limited reflection on the physicochemical characteristics of the degradation products generated in vivo, which are very different from individual metal particles and/or ions obtained from different commercial sources. In this study, we aimed to understand the differences in toxicity induced by the degradation products in as-synthesized form as well as those obtained after post-processing. The degradation products were generated using a hip-simulator by maintaining physiological conditions closer to in vivo and separated into two batches, one with processing by washing and drying called processed degradation products (PDP) and another batch as 'as-synthesized' degradation product (DP). We studied the dose-dependent toxicity response by neural cells derived from induced pluripotent stem cells. The results of the study show that as-synthesized DPs are more toxic to neural cells even at lower concentrations studied with evident low TC50 (1-5 µg/ml) concentrations compared to PDP (25 µg/ml). Flow cytometric analysis showed a significant (p<.01) increase in uptake of the particles after 24 h and corresponding ROS production in DP-treated cells. RT-PCR analysis of oxidative specific gene expression showed, elevated mRNA levels of NADPH oxidase-1, nuclear transcription factor, superoxide dismutase-2 and glutaredoxin-2 in DP-treated cells after 6 h. The results of the study provided a clear evidence of the differential response of neural cells on the degradation products as a function of concentrations and their chemical nature.

The effect of the inflammatory species hypochlorous acid on the corrosion and surface damage of Ti-6Al-4V and CoCrMo alloys.

Performance of metallic orthopedic alloys is dependent on the local biological conditions within the joint. Inflammation within a joint can lead to severe conditions at the surface of the implant and may represent a driving force of corrosion which is not well understood. In this study, the corrosion response of CoCrMo and Ti-6Al-4V alloys was studied in hypochlorous acid (HOCl) saline solutions, which served as a simulated inflammatory environment. Anodic polarization and electrochemical impedance spectroscopy were used to evaluate the electrochemical behavior of these alloys in a range of hypochlorous acid solutions. The open circuit potential of CoCrMo rose to over 600 mV (vs. Ag/AgCl) in 30 mM HOCl solutions while the corresponding corrosion current increased three orders of magnitude over controls. Visual analysis of CoCrMo disks after immersion in 50 mM HOCl for 5 days revealed extensive surface damage. This study shows that HOCl can polarize CoCrMo surfaces above the transpassive potential without an external power source. Ultimately, long-term exposure to HOCl within an inflamed joint may significantly affect patient outcomes through accelerated generation of corrosion products. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3185-3194, 2018.

Can gamma irradiation during radiotherapy influence the metal release process for biomedical CoCrMo and 316L alloys?

The extent of metal release from implant materials that are irradiated during radiotherapy may be influenced by irradiation-formed radicals. The influence of gamma irradiation, with a total dose of relevance for radiotherapy (e.g., for cancer treatments) on the extent of metal release from biomedical stainless steel AISI 316L and a cobalt-chromium alloy (CoCrMo) was investigated in physiological relevant solutions (phosphate buffered saline with and without 10 g/L bovine serum albumin) at pH 7.3. Directly after irradiation, the released amounts of metals were significantly higher for irradiated CoCrMo as compared to nonirradiated CoCrMo, resulting in an increased surface passivation (enhanced passive conditions) that hindered further release. A similar effect was observed for 316L showing lower nickel release after 1 h of initially irradiated samples as compared to nonirradiated samples. However, the effect of irradiation (total dose of 16.5 Gy) on metal release and surface oxide composition and thickness was generally small. Most metals were released initially (within seconds) upon immersion from CoCrMo but not from 316L. Albumin induced an increased amount of released metals from AISI 316L but not from CoCrMo. Albumin was not found to aggregate to any greater extent either upon gamma irradiation or in the presence of trace metal ions, as determined using different light scattering techniques. Further studies should elucidate the effect of repeated friction and fractionated low irradiation doses on the short- and long term metal release process of biomedical materials. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2673-2680, 2018.

Graphene coating on the surface of CoCrMo alloy enhances the adhesion and proliferation of bone marrow mesenchymal stem cells.

The objective was to investigate whether a graphene coating could improve the surface bioactivity of a cobalt-chromium-molybdenum-based alloy (CoCrMo). Graphene was produced by chemical vapor deposition and transferred to the surface of the CoCrMo alloy using an improved wet transfer approach. The morphology of the samples was observed, and the adhesion force and stabilization of graphene coating were analyzed by a nanoscratch test and ultrasonication test. In an in vitro study, the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) cultured on the samples were quantified via an Alamar Blue assay and cell counting kit-8 (CCK-8) assay. The results showed that it is feasible to apply graphene to modify the surface of a CoCrMo alloy, and the enhancement of the adhesion and proliferation of BMSCs was also shown in the present study. In conclusion, graphene exhibits considerable potential for enhancing the surface bioactivity of CoCrMo alloy.