CoCrMo Alloy Surfaces Research Articles

THE EFFECT OF A COMPOSITE CHITOSAN-SILVER(I) ION COATING ON THE CORROSION RESISTANCE OF THE COBALT-CHROMIUM-MOLYBDENUM ALLOY IN SALINE SOLUTION

We determined the in vitro corrosion resistance of the composite chitosan-silver(I) [Ag(I)] ion coating on the cobalt-chromium-molybdenum (CoCrMo) dental alloy in a 0.9% sodium chloride (NaCl) solution at 37°C. We obtained the novel composite chitosan–Ag(I) ion coating by electrophoretic deposition at 20 V for 30 s at room temperature in a 2% (v/v) aqueous solution of acetic acid with 1 g dm–3 chitosan and 10 g dm–3 silver nitrate. We evaluated the chemical composition with energy dispersive spectroscopy and Fouriertransform infrared spectroscopy. We investigated surface topography and electronic properties with a scanning Kelvin probe. We determined the mechanism and kinetics of the electrochemical corrosion of the obtained coatings by electrochemical impedance spectroscopy. The Ag content in the composite chitosan–Ag(I) ion coating was 1.9 ± 1 wt.%. The cataphoretic co-deposition of chitosan and Ag(I) ions in an aqueous solution can be used to modify the CoCrMo alloy surface to obtain new coatings with antibacterial properties.

Effect of boriding on high temperature tribological behavior of CoCrMo alloy

In the present work, CoCrMo alloy surfaces were subjected to powder-pack boriding at 950 ℃ for 5-hour and 7-hour treatment periods. The obtained boride layers were characterized with scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, nanoindentation and high temperature wear tests. Characterization results show that boride layers are composed of CoB, Co2B, CrB and Co2MoB2 phases. Up to 4-fold increase is achieved in nanohardness values due to the boride layers in addition to increased elastic moduli. Increased surface hardness coupled with the high temperature stability of boride layers led to nearly 12, 7 and 10-fold increase in the wear resistance of CoCrMo alloys, worn at room temperature, 250 ℃ and 500 ℃, respectively.

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

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 invitro and whether electrocautery damage to alloy surfaces may hasten this process. Murine macrophages were cultured on CoCr disks with and without damage from a monopolar electrocautery. Culture medium was replaced every 12hours 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. 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. 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.

Interactions between hyaluronic acid and CoCrMo alloy surface in simulated synovial fluids

The performance of CoCrMo alloy in orthopaedic implants may be unfavourably affected by hyaluronic acid (HA) in synovial fluid. In this study, the authors aimed to understand the interactions between HA and CoCrMo using dedicated electrochemical experiments and surface analyses. A sequence of electrochemical measurements (open-circuit potential, linear polarization resistance, potentiodynamic and potentiostatic polarizations) was run on LC-CoCrMo (ASTM F1537) in Dulbecco's phosphate-buffered saline (DPBS) solution with and without HA and in DPBS mixed with newborn calf serum (NCS) and HA, partially under simultaneous recording of surface pH using custom-made microelectrodes. Samples were analysed by optical and electron microscopy. HA had no significant impact on the corrosion potential of CoCrMo alloy (ECORR = −173 ± 8, −211 ± 16, and −254 ± 30 mVAg/AgCl, in DPBS, DPBS + HA, and DPBS + NCS + HA, respectively). Average current density values at the transpassive domain were double in DPBS compared to DPBS + HA and DPBS + NCS + HA. At potentials above +0.6 VAg/AgCl, surface pH values decreased from 7.5 to 6.5 in DPBS and from 7.5 to below 4 in DPBS + HA. In conclusion, the presence of HA did not compromise the corrosion resistance of CoCrMo alloy at free potential, but it enhanced acidic conditions at the near surface under anodic-applied potential in the transpassive domain.

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

IntroductionWith 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.MethodsIn 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.ResultsThe 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.DiscussionThis 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.

Tribological Performance of Artificial CoCrMo Prosthesis by ELID Grinding Process

The demand for CoCrMo alloy as an artificial prosthesis has increased for its reliable properties. However, machining of CoCrMo alloy is challenging due to meet the high requirements on prosthesis’ surface quality. In this paper, a new approach of fine ELID grinding on CoCrMo alloy has been proposed using a Kistler three-component dynamometer to monitor the grinding force in real time. This paper also presents the friction and wear performance of CoCrMo alloy. Results show that better efficiency and surface quality can be obtained with low feed speed and small grinding depth. The passivation layer was found on the surface of CoCrMo alloy after ELID grinding, which makes the CoCrMo alloy prosthesis have better biocompatibility. The wear resistance test has proved that CoCrMo alloy has better wear resistance and lower wear quality and is suitable for manufacturing prosthesis.

Effect of grain size and crystallographic structure on the corrosion and tribocorrosion behaviour of a CoCrMo biomedical grade alloy in simulated body fluid

CoCrMo alloys are used in hip and knee replacements due to their excellent long-term survival rates. However, high failure rates have recently been observed associated with adverse tissue reactions. CoCrMo alloy surfaces undergo microstructural changes during wear, including the formation of ε-martensite and, occasionally, a nanocrystalline surface layer. It is not clear whether these changes are beneficial or detrimental to the performance of the component. Thus, high-pressure torsion (HPT) was employed to produce different grain sizes and crystallographic structures in a CoCrMo alloy and the corrosion and tribocorrosion behaviour were critically investigated as a function of grain size. The results reveal a degradation of the corrosion resistance for the HTP processed samples. The contributions of mechanical and corrosion material loss in tribocorrosion is also examined.

Chemical, Electrochemical, and Surface Study on Microbial Attack of CoCrMo Dental Alloy by Streptococcus mutans

In this investigation, the objective of our research was to evaluate the influence of the corrosion behavior of CoCrMo dental alloy in the presence of the oral bacteria Streptococcus mutans (Streptococcus mutans) and its growth byproducts. The corrosion resistance of the dental alloy CoCrMo followed a comparative study in the sterilized Fusayama’s artificial saliva (FAS) containing Trypticase soy broth (TSB) (medium 1) and Streptococcus mutans mixed with (TSB) and (FAS) (medium 2). To perform this study, electrochemical corrosion tests including open circuit potential (OCP), potentiodynamic polarization (PDP), and impedance spectroscopy (EIS) measurements and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used. The formed films biomass was observed by an optical microscope, after 216 h (9 days) of exposition to medium containing Streptococcus mutans; then, it was verified by SEM–EDS analysis. The results of the electrochemical corrosion showed a significant shift of the corrosion potential and an increase in the corrosion current density (icorr) and the corrosion resistance (Rp) after 24 h of immersion of the alloys in the medium containing Streptococcus mutans. This led to alter the formation of the passive film which reveals the high reactivity of CoCrMo in the presence of Streptococcus mutans, whereas the surface analysis confirmed the biofilm formation once the contact of Streptococcus mutans to CoCrMo alloy surfaces was insured.

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.

Effect of surface energy on protein adsorption behaviours of treated CoCrMo alloy surfaces

CoCrMo alloys have been used as biomedical materials for decades. During long-term service in the body environment, however, proteins adsorbing onto the surface of implant can cause their spontaneous corrosion and even the release of toxic ions, which may cause long-term damage to patients. It is essential to understand the key factors affecting protein adsorption and how it can alter corrosion reactions. In this study, the surface energy of a CoCrMo alloy was changed through various oxidation processes. Surface analysis techniques, such as XPS, AES, and GIXRD were used to characterise the chemical properties of the surfaces of modified CoCrMo alloys. Surface topography and potential images of samples after bovine serum albumin (BSA) adsorption were acquired by AFM/SKPFM. The results show that with the increase of the oxidation temperature, the hydrophilicity of the samples was enhanced. With the increase in oxidation time at the same temperature, the surface energy of the samples increased, the dispersion component increased, and the polar component decreased. As a result, the amount of BSA adsorbed on the surfaces decreased, and this was affected more by the polar component than by other components, which was due to the electrostatic and hydrophobic interactions.

Effects of laser processing conditions on wettability and proliferation of Saos-2 cells on CoCrMo alloy surfaces

Abstract Any processing disturbances in laser surface texturing (LST) could compromise the resulting surface topography and their desired functional response. Disturbances such as focal plane offsets and beam incident angle variations are always present in LST processing of 3D parts and can affect the surface morphology. In this research the effects of these laser processing disturbances in producing laser induced surface structures (LIPSS) on CoCrMo alloy substrates were investigated. In particular, these two disturbances were considered as laser processing variables to determine their effects on functional responses of LIPSS treated surfaces, i.e. surface wettability and the proliferation of Saos-2 osteoblast-like cells were evaluated. It was found that the changes of laser processing conditions led to a decrease in surface wettability and Saos-2 cells proliferation. In addition, a correlation between surface wettability and cell proliferation on LIPSS treated surface was identified and conclusions made about the effects of investigated process disturbances on the functional response of LIPSS treated CoCrMo substrates.

A fluorescent approach for detecting and measuring reduction reaction byproducts near cathodically-biased metallic surfaces: Reactive oxygen species production and quantification

During tribocorrosion of biomedical alloys, potentials may shift cathodically across the metal-oxide-electrolyte interface resulting in the increased reduction of local oxygen and water molecules. The products of reduction are thought to include reactive oxygen species (ROS) as well as hydroxide ions. Using fluorescent probes, developed for labeling intracellular ROS-based hydroxyl radicals (OH·) and hydrogen peroxide (H2O2), ROS generation due to reduction reactions at cathodically biased CoCrMo alloy surfaces was measured directly. Using terephthalic acid (TA) and pentafluorosulfonylbenzene-fluorescein (PFF) as fluorescent dosimeters, it was found that OH· and H2O2 concentrations increased up to 16 h and 2 h, respectively. Decreases in fluorescence past these time points were attributed to the continuous onset of reduction reactions consuming both the ROS and/or dosimeter. It was also found that voltages below and including −600 mV (vs. Ag/AgCl) produced measurable quantities of H2O2 after two hours of polarization, with concentrations increasing with decreasing potentials up to −1000 mV. The detection and quantification of ROS in a clinical setting could help us better understand the role of ROS in the inflammatory response as well as their impact on corrosion behavior of biomedical alloys.

Response of Saos-2 osteoblast-like cells to laser surface texturing, sandblasting and hydroxyapatite coating on CoCrMo alloy surfaces

Cobalt chrome alloys are commonly used in orthopaedic implants where high stiffness and wear resistance are required. This study proposes Laser Surface Texturing (LST) as a cost-effective mean for producing bioinspired surface textures in order to improve the performance of CoCrMo orthopaedic implants. Cobalt-chrome alloy disks were modified using three different LST strategies: i) micro-scale texturing using a nanosecond laser source; (ii) micro-scale texturing with an ultrashort laser source and (iii) bioinspired sub-micron scale texturing with an ultrashort laser source. The modified disks were characterized and compared to blasted, hydroxyapatite coated and polished surface finishes. Saos-2 osteoblast-like cells were seeded on the different surfaces and their proliferation and morphology was assessed. The laser modification increases the surface energy of the CoCrMo alloy disks when compared to their untreated counterparts. The bioinspired sub-micron textured surfaces exhibited the highest cell metabolic activity on day 7 of the MTT assay.

Tribo-corrosion and Albumin Attachment of Nitrogen Ion-Implanted CoCrMo Alloy During Friction Onset

In this paper, CoCrMo alloy surface was implanted with 100 keV nitrogen ions to modify it. Bovine serum albumin (BSA) adsorption and the initial behavior of tribo-corrosion in the simulated system were studied. Nitrogen ion implantation can promote BSA dynamic adsorption due to the change of friction and wear mechanisms. From the tribo-corrosion test results, the open circuit potential (OCP) increased to about 0.6 V and the coefficient of friction (COF) decreased to about 0.2 for the nitrogen ion-implanted CoCrMo compared with the untreated sample before the modified layer failure. The point when the open circuit potential and the coefficient of friction changed during long wear time (1, 2 and 4 h) is considered the sign of the worn through modified layer. Then, the OCP of the implanted sample rose by 0.3 V compared with the untreated sample, and the COF remained at around 0.3, which is lower compared with the COF of untreated sample after the modified layer has been worn through. Thus, nitrogen ion implantation not only improved wear and corrosion resistance of the CoCrMo alloy, but also promoted BSA adsorption on the CoCrMo alloy surface, which effectively reduced the wear volume and metal ions release.

Growth Kinetics of CoB–Co2B Layers Using the Powder-Pack Boriding Process Assisted by a Direct Current Field

Abstract New results about the growth kinetics of CoB–Co2B layers developed at the surface of CoCrMo alloy using the powder-pack boriding process assisted by a direct current field (PBDCF) were estimated in this work. The PBDCF was conducted at temperatures of 1048 – 1148 K with different exposure times for each temperature, whereas the growth kinetics of the cobalt boride layers was modelled using a system of two differential equations. In addition, indentation properties such as hardness, Young’s modulus and residual stresses were estimated along the depth of the borided CoCrMo surface. The growth kinetics of the cobalt boride layers developed by PBDCF indicated that thicker boride layers were formed on the material’s surface which was in contact to the current field at the anode, in contrast to the surface exposed at the cathode. The kinetics of cobalt boride layers were compared with those obtained by conventional powder-pack boriding process.

A Preliminary Study to Enhance the Tribological Performance of CoCrMo Alloy by Fibre Laser Remelting for Articular Joint Implant Applications

CoCrMo alloy has long been used as a pairing femoral head material for articular joint implant applications because of its biocompatibility and reliable tribological performance. However, friction and wear issues are still present for CoCrMo (metal)/CoCrMo (metal) or CoCrMo (metal)/ultrahigh molecular weight polyethylene (UHMWPE) (plastic) pairs in clinical observations. The particulate wear debris generated from the worn surfaces of CoCrMo or UHMWPE can pose a severe threat to human tissues, eventually resulting in the failure of implants and the need for revision surgeries. As a result, a further improvement in tribological properties of this alloy is still needed, and it is of great interest to both the implant manufacturers and clinical surgeons. In this study, the surface of CoCrMo alloy was laser-treated by a fibre laser system in an open-air condition (i.e., no gas chamber required). The CoCrMo surfaces before and after laser remelting were analysed and characterised by a range of mechanical tests (i.e., surface roughness measurement and Vickers micro-hardness test) and microstructural analysis (i.e., XRD phase detection). The tribological properties were assessed by pin-on-disk tribometry and dynamic light scattering (DLS). Our results indicate that the laser-treated surfaces demonstrated a friction-reducing effect for all the tribopairs (i.e., CoCrMo against CoCrMo and CoCrMo against UHHMWPE) and enhanced wear resistance for the CoCrMo/CoCrMo pair. Such beneficial effects are chiefly attributable to the presence of the laser-formed hard coating on the surface. Laser remelting possesses several competitive advantages of being a clean, non-contact, fast, highly accurate and automated process compared to other surface coating methods. The promising results of this study point to the possibility that laser remelting can be a practical and effective surface modification technique to further improve the tribological performance of CoCr-based orthopaedic implants.

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.

Effect of simulated inflammatory conditions and potential on dissolution and surface oxide of CoCrMo alloy: In situ electrochemical atomic force microscopy study

Inflammation may develop in association with implantation of hip replacements and the inflammatory state of the local body fluids may affect the corrosion of metallic biomaterials like CoCrMo alloy. In this study CoCrMo alloy surfaces were imaged using in situ electrochemical atomic force microscopy (ECAFM) to evaluate oxide film morphology and surface dissolution while immersed in phosphate buffered saline (PBS) solution or simulated inflammatory (SI) solutions across a range of potentials. The SI solution explored here consisted of a 30 mM hydrogen peroxide (H2O2) modified PBS solution. Analysis of ECAFM images, surface roughness and potentiostatic polarization current density data exhibited a correlated relationship between surface oxide morphology, loss of passivity and electrochemical behavior CoCrMo alloy. ECAFM results showed that the presence of H2O2 altered oxide film behavior, leading to positive shifts of open circuit potential (OCP) to 0.32 V (vs Ag/AgCl), higher current density and significantly altered oxide film topography compared to PBS only case. Surface morphology, surface roughness (Ra) and current density exhibited strong potential- and time-dependent behaviors. Significant surface oxide formation on alloy and carbides were observed, followed by dissolution of CoCrMo alloy as potentials were increased above 0.5 V. Carbide boundaries and metal grain boundaries were preferential sites for oxide dissolution at transpassive potential ranges. Formation and evolution of new oxides were directly imaged at 0.65 V in PBS solution. New oxides formed and covered the surface in 10 min at 0.65 V. However, they were less protective compared to the passive oxide films at OCP condition. Simulated inflammatory solutions raise alter corrosion behavior of CoCrMo alloys.

The effect of simulated inflammatory conditions and pH on fretting corrosion of CoCrMo alloy surfaces

Inflammation may develop due to the implantation of orthopedic devices and inflammatory cell-based chemical species may affect the fretting corrosion behavior of CoCrMo alloy. The effect of simulated inflammatory (SI) conditions and acid on the fretting corrosion behavior of CoCrMo was studied. SI conditions included phosphate buffered saline (PBS) with H2O2 and PBS with Fenton reaction (Fe3+, H2O2). Fretting corrosion behavior of CoCrMo alloy was significantly affected by both the Fenton reaction-based solution chemistry and potential. The Fenton reaction increased the oxidizing power of the solution and led to a significant rise in open circuit potential (OCP) during fretting corrosion compared to PBS and pH 3 solutions (p< 0.05). SI conditions also altered the oxide film characteristics, altering both the fretting corrosion response of CoCrMo alloy (smaller fretting currents by about 50%) and the frictional behavior compared to the PBS case. Fretting current density in Fenton reaction conditions was significantly smaller compared to PBS conditions at all potentials, indicating the oxide film was less protective due to the presence of Fenton reactions. A significantly higher coefficient of friction was observed in Fenton reaction solutions at −0.4V (0.5) and −0.6V (0.55) compared to all other conditions. This appears to be related to the oxide formation potential (−0.4V) and the effects of solution chemistry on sliding mechanics. Passivation of oxide film was the strongest in pH 3 condition, where baseline current density was the lowest at 0.6V compared to that of other solutions (p< 0.05).

Electrosurgery Induced Damage to Ti-6Al-4V and CoCrMo Alloy Surfaces in Orthopedic Implants In Vivo and In Vitro

BackgroundRecent observations of specific metal damage patterns on retrieved total joint implants implied a cellular origin and was termed inflammatory cell-induced (ICI) corrosion. Although ICI corrosion continues to present a potential damage source for metallic biomaterials surfaces, an alternate source of some damage patterns may arise from electrosurgery instruments in total joint arthroplasty. MethodsTo characterize electrosurgically-induced damage patterns on metal implants, a model system of highly polished CoCrMo and Ti-6Al-4V disks and commercial electrosurgical generator was evaluated in various modes and power settings using monopolar and bipolar configurations. Surfaces were tested dry, wet with phosphate-buffered saline, or covered with known thicknesses of hydrated 5% agarose hydrogel. ResultsIn all cases, surface damage was generated on both alloy surfaces, directly resulting from plasma discharge interacting with the metal. Direct surface contact caused pitting and oxide buildup at the contact area. Damage was produced through 3 mm thickness of hydrogel on the surface and across metal-metal junctions representing modular tapers. Damage patterns on wetted surfaces were highly consistent with damage patterns observed on retrieved total joint implants; circular, ruffled areas with centralized pits, occasionally presenting trail- and weld-like features. ConclusionSurgeons using electrosurgical systems in proximity to metallic implants should exercise caution. Discharge of electrical energy through implants can induce localized surface damage and may result in other adverse outcomes. Although these results show some damage reported to be ICI corrosion is indeed the result of electrosurgery, there remains damage observed in retrievals not explained by this process.