Orthopaedic Alloys Research Articles

Effect of Heat Treatment on Microstructure and Mechanical Properties of a Ti-Mo-Zr Alloy

Recently there is increasing demand for the development of new -type titanium with a low elastic modulus for surgical orthopaedic implant applications. In this paper, we developed a new Ti-Mo-Zr alloy based on the d-electron alloy design theory. The designed Ti-12Mo-5Zr (at%) alloy was then produced using ingot metallurgy and evaluated pertaining to the effect of heat treatment on the microstructure and mechanical properties. The alloy exhibited a relatively low Young’s modulus similar to some typical  orthopaedic titanium alloys. Yield strength, tensile strength and Young’s modulus of the alloy decreased after solid solution treatment. The mechanism by which heat treatment affects the mechanical properties is discussed.

Mechanism of Chromium Oxide Formation in Cobalt–Chromium–Molybdenum (F75) Alloys Prepared Using Spark Plasma Sintering

AbstractMetallic implants are known to have higher wear rates compared to ceramic. This causes more wear debris to be produced and results in the release of toxic metal ions to the surrounding areas. The strengthening mechanism in cobalt based cast orthopedic alloys depends upon carbides present in the microstructure, but these cause problems when dislodged between articulating surfaces, accelerating wear by abrasion and fretting. Thus, in order to improve the performance of these implants a novel method of processing the alloys, namely by spark plasma sintering (SPS) of fine powders, has been used as it generates hard oxides and not carbides in the microstructure. The oxide in the SPS processed alloy is identified as chromium oxide formed by a redox reaction between cobalt oxide found on the surface of cobalt particles and chromium. The oxygen associated with the cobalt powder is displaced and combines with the chromium during SPS. This oxide in the microstructure of the alloy can be more beneficial than carbides due to its higher hardness, resulting in lower wear rates and less wear particles. With the oxide in the microstructure, the hardness of the alloy becomes closer to that of ceramics. Also its lower density enables the alloy to be lighter. The chemical stability of the oxide ensures that it remains intact and due its insolubility in water, no carcinogenic or toxic reactions will occur.

Inflammatory response to orthopaedic cobalt chromium alloy wear debris in a rodent air pouch model

Cobalt chromium (Co-Cr) alloy metal-on-metal (MOM) hip resurfacing has become increasingly common in younger, more active patients. However, there is growing concern regarding levels of Co-Cr wear debris and ions released. Using the rodent air pouch model, described as a facsimile synovium, we assessed the inflammatory response to artificially generated Co-Cr wear debris.

Toxic effects of Senecio brasiliensis on rat phagocytes

s / Toxicology Letters 196S (2010) S37–S351 S199 P205-022 Allergen-stimulated expression of interleukin (IL)-17 isoforms in mice I. Kimber, M. Hayes, R. Dearman University of Manchester, United Kingdom The development of immune and allergic responses is orchestrated by T helper (Th) subsets that are characterized by selective cytokine secretion profiles. Topical exposure of BALB/c strain mice to different classes of chemical allergen has been shown to result in preferential activation of divergent Th cell subsets. Thus, Th1 and Th2 cells are induced by the contact allergen 2,4-dinitrochlorobenzene (DNCB) and the respiratory sensitizer trimellitic anhydride (TMA), respectively. A further subset of inflammatory Th cells that secrete IL-17mayplay an important role in some autoimmune and inflammatory conditions. In the current investigations, the ability of chemical allergens to provoke changes in expression of the expression of IL-17 isoforms has been examined. BALB/c strain mice were exposed to a single topical dose of either 1% DNCB or 25% TMA, or to vehicle alone, for 30min to 72h. At various times thereafter, cytokine production by skin explants (prepared from dorsal halves of ear tissue) or by draining auricular lymph node cells (LNC) was measured by cytokine-specific enzyme-linked immunosorbant assay (ELISA). Topical treatment with DNCB, but not to TMA or vehicle alone, provoked a rapid increase in IL-17A and IL-17F isoforms, peaking at 2–3h. Levels of IL-17F were generally some 5-fold higher than those observed for IL-17A. DNCB-activated LNC also produced high levels of both IL-17A and IL-17F, reaching maximal levels after 6h of exposure. The heterodimer (IL-17A/F) was also detected, but at considerably lower levels. Treatment with TMA induced the same pattern of cytokines in the draining lymph node, but with slightly delayed kinetics, peaking at 48–72h. These data demonstrate that chemical allergens provoke the rapid production of IL-17 isoforms in the skin and draining lymph node which may play a role in the acquisition of sensitization. doi:10.1016/j.toxlet.2010.03.673 P205-023 Toxic effects of Senecio brasiliensis on rat phagocytes F. Elias1, I. Hueza2, A. Latorre1, S. Gorniak1 1 University of Sao Paulo/Research Center of Veterinary Toxicology (CEPTOX), Brazil, 2 Federal University Of Sao Paulo/School of Pharmacy and Biochestry, Brazil Senecio brasiliensis is one of the most toxic poisonous plant species of Senecio’s genus. It contains pyrrolizidine alkaloids (PAs) that are associated with disease in livestock and human beings after be metabolized into the liver in a high reactive electrophiles (pyrrol compound) capable to link with cellular macromolecules, mainly DNA, forming adducts which may initiate acute or chronic toxicity. The development of oxidative stress with the generation of superoxides and lipid-peroxy radicals in PAs toxicity in cattle and cytotoxicity to macrophages mediated by reactive oxygen species were recently documented. Therefore, the aim of this study was to verify if S. brasiliensis induce toxicity in innate immune system cells (macrophages and neutrophils) during phagocytosis activity. PAs was extracted and concentrated into a butanolic residue (BR) and rats were then treated with BR daily, by gavage, during 28 days. Two experiments were performed, one to evaluate peritoneal macrophages and the other to determine peripheral neutrophils activity. For each experiment 40 adult rats were separated into four groups treated with 0.0 (control), 3.0 (A), 6.0 (B), and 9.0 (C)mg/kg of BR. The results obtained showed a significant enhancement in basal (Aand C-group) and PMA induced (C-group) oxidative burst of peritoneal macrophages and also an increase percentage of macrophage phagocytosis (A-, B-, and Cgroup). However, in relation to neutrophils activities, it was only observed an increase in basal oxidative burst (Aand B-group). The intracellular redox potential is maintained in a reduced state by constant elimination of superoxides, peroxides and cellular H2O2 by glutathione (GSH). The pyrrolic metabolites produced from PAs are capable tobindwithGSHto formGSHconjugates. Thus, it is possible to hypothesized that, one of themechanism that S. brasiliensis exerts its immunotoxicity onmacrophage and neutrophil activities is by depleting GSH. doi:10.1016/j.toxlet.2010.03.674 P205-024 Inflammatory response to orthopaedic cobalt chromium alloy wear debris in a rodent air pouch model M. Akbar1, M.H. Grant1, J. Brewer2 1 University of Strathclyde, United Kingdom, 2 University of Glasgow,

Tribochemical Component of Oxidizing Stress Development at Joint Replacement. Part I. Determination of Radical-Forming Ability of Wear Particles from Various Orthopaedic Materials

Using the model reaction of cumene oxidation the radical-forming ability of wear particles of some orthopaedic alloys and corundum ceramics were studied. It was revealed that wear particles from different alloys catalyzed cumene oxidation whereas particles of corundum ceramics were inert. Cobalt alloy wear particles were much more active as compared with the titanium alloy and stainless steel particles. Production of cobalt alloy by laser sintering reduced the radical-forming ability of its wear particles. Activity of cobalt wear particles was preserved for a long time after their formation and could considerably strengthen the development of oxidizing stress at joint arthroplasty. Detection of catalytic activity of orthopaedic alloys' wear particles requires studying of the influence of free radicals generated by tribochemical reaction upon implant components and biological tissues.

A novel route for processing cobalt-chromium-molybdenum orthopaedic alloys.

Spark plasma sintering has been used for the first time to prepare the ASTM F75 cobalt-chromium-molybdenum (Co-Cr-Mo) orthopaedic alloy composition using nanopowders. In the preliminary work presented in this report, the effect of processing variables on the structural features of the alloy (phases present, grain size and microstructure) has been investigated. Specimens of greater than 99.5 per cent theoretical density were obtained. Carbide phases were not detected in the microstructure but oxides were present. However, harder materials with finer grains were produced, compared with the commonly used cast/wrought processing methods, probably because of the presence of oxides in the microstructure.

Biocompatibility of uncoated and diamond-like carbon coated Ti–20%Hf alloy

Biocompatibilities of uncoated and diamond like carbon (DLC) coated Ti–20%Hf alloy have been investigated by means of 3T3 mouse fibroblast cell viability quantification using flow cytometry. For comparison, similar tests were performed for pure Ti, Hf, and V as well as a commercial orthopaedic alloy, Ti–6Al–4V. Under the test conditions used, the biocompatibilities of uncoated and DLC coated Ti–20%Hf alloy, pure Hf, and Ti–6Al–4V alloy were comparable to that of pure Ti, a metal known for its superior biocompatibility, while pure V clearly exhibited the lowest biocompatibility of all the materials that were evaluated. The addition of Hf to Ti resulted in significant solid solution strengthening and at 20%Hf concentration the hardness of this alloy was comparable to that of the Ti–6Al–4V alloy. Ti–Hf alloys and wear resistant, low friction DLC coatings may either be used in conjunction with or may independently hold promise for orthopaedic implants and possibly other biomedical applications.

The treatment of femoral neuropathy due to pseudotumour caused by metal-on-metal resurfacing arthroplasty

Concerns now exist about the long-term biological effects of exposure to orthopaedic metal alloys, particularly serum cobalt and chromium ions derived from metal-on-metal wear debris in these patients. A pseudotumour mass complicating metal-on-metal resurfacing arthroplasty has been recognized by orthopaedic oncologists and specialist hip units. Pseudotumours may also present with a major nerve palsy. Two cases of femoral neuropathy due to pseudotumour masses caused by metal-on-metal resurfacing arthroplasty are presented. Preoperative neurophysiological studies showed severe and irreversible pathological changes to nerve function with neurohistopathological evidence of complete nerve destruction with a previously unreported pathological appearance. This may represent a previously unrecognized pathological process, possibly 'toxic' in nature, resulting from metal-on-metal wear debris. Prolonged follow-up and detailed clinical assessment of patients after hip resurfacing arthroplasty is advocated with planned and expeditious revision of any patient in whom evidence of femoral neuropathy develops.

Reactive Plasma‐Aided RF Sputtering Deposition of Hydroxyapatite Bio‐implant Coatings

AbstractThe plasma‐assisted RF sputtering deposition of a biocompatible, functionally graded calcium phosphate bioceramic on a Ti6Al4 V orthopedic alloy is reported. The chemical composition and presence of hydroxyapatite (HA), CaTiO3, and CaO mineral phases can be effectively controlled by the process parameters. At higher DC biases, the ratio [Ca]/[P] and the amount of CaO increase, whereas the HA content decreases. Optical emission spectroscopy suggests that CaO+ is the dominant species that responds to negative DC bias and controls calcium content. Biocompatibility tests in simulated body fluid confirm a positive biomimetic response evidenced by in‐growth of an apatite layer after 24 h of immersion.

Laser‐deposited Ti‐Nb‐Zr‐Ta orthopedic alloys

The complex quaternary Ti-35Nb-7Zr-5Ta orthopedic alloy has been successfully deposited from a powder feedstock consisting of a blend of elemental titanium, niobium, zirconium, and tantalum powders, using the laser engineered net-shaping (LENStrade mark) process. In the as laser-deposited form, these alloys exhibit a substantially higher tensile strength as compared with more conventionally processed counterparts of similar composition, while maintaining excellent ductility and a low modulus. Furthermore, the as-deposited alloys appear to exhibit a <001> texture, with a substantially large number of grains of the beta phase aligning one of their <001> axes nearly normal to the substrate or parallel to the growth direction. The microstructure of the as-deposited as well as tensile-tested alloys have been characterized in detail using scanning electron microscopy (SEM), orientation microscopy (OM), and transmission electron microscopy (TEM). Formation of a high density of shear bands, possibly arising from slip localization due to precipitates of the omega phase in the beta matrix, is clearly evident in the tensile-tested sample. The enhanced tensile strength and low modulus in these laser-deposited alloys coupled with the ability to form near-net shape components makes LENS an attractive processing technology for orthopedic implants.

Metal ion release from nitrogen ion implanted CoCrMo orthopedic implant material

CoCrMo alloys are used as orthopedic implant materials because of their excellent mechanical and corrosion properties. However, when placed in vivo, these alloys release Co, Cr, Mo ions to host tissues, which may give rise to significant health concerns over time. Nitrogen ion implantation can be used to form protective layers on the surface of CoCrMo orthopedic alloys by modifying the near surface layers of these materials. In this study, medical grade CoCrMo alloy (IS0 5832-12) was ion implanted with 60 keV nitrogen ions to a high dose of 1.9 × 10 18 ions/cm 2 at substrate temperatures of 100, 200 and 400 °C. The N implanted layer microstructures, implanted layer phases, and thicknesses were studied by a combination of Bragg–Brentano ( θ/2 θ) and grazing incidence (Seeman–Bohlin) X-ray diffraction (XRD and GIXRD) and cross-sectional scanning electron microscopy (SEM). Atomic force microscopy (AFM) was used for roughness analysis of N implanted as well as as-polished surfaces. Static immersion tests were performed to investigate metal ion release into simulated body fluid (SBF) by electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma optical emission spectrometry (ICP-OES). XRD and SEM analyses indicated that the N implanted layers were ∼ 150–450 nm thick and composed of the (Co,Cr,Mo) 2+ x N nitride phase and a high N concentration Co-based FCC phase, γ N depending on the substrate temperature. ETAAS analysis results showed that in vitro exposure of the N implanted surfaces resulted in higher levels of cobalt ion release into the simulated body fluid compared to the untreated, polished alloy. The higher Co release from the N implanted specimens is attributed to the nature of the implanted layer phases as well as to the rougher surfaces associated with the N implanted specimens compared to the relatively smooth surface of the untreated material. SEM analysis of N implanted and untreated specimens after immersion tests clearly indicated calcium phosphate formation on the as-polished CoCrMo alloy, indicating a degree of bioactivity of the untreated metal surface which is absent in the N implanted specimens.

Enhanced wear resistance of Ti-5Al-2Nb-1Ta orthopaedic alloy by nitrogen ion implantation

The tribological properties of nitrogen implanted Ti-5Al-2Nb-1Ta orthopaedic alloy was studied by performing lubricated pin on disc tests against ultra high molecular weight polyethylene pins. The results were interpreted on the basis of friction coefficient, wear volume loss and by characterising the wear debris to understand the wear mechanism. The results indicated a decrease in wear rate for implanted samples. Detailed investigations of the dose dependence on wear performance were carried out. The friction and wear data show a clear transition in wear modes between implanted and unimplanted alloys. The wear debris confirms the presence of titanium oxide and titanium oxynitride phases for untreated and nitrogen implanted alloy.

RF Plasma Sputtering Deposition of Hydroxyapatite Bioceramics: Synthesis, Performance, and Biocompatibility

AbstractSummary: Hydroxyapatite (HA) coatings have numerous applications in orthopedics and dentistry, owing to their excellent ability to promote stronger implant fixation and faster bone tissue ingrowth and remodeling. Thermal plasma spray and other plasma‐assisted techniques have recently been used to synthesize various calcium phosphate‐based bioceramics. Despite notable recent achievements in the desired stoichiometry, phase composition, mechanical, structural, and biocompatible properties, it is rather difficult to combine all of the above features in a single coating. For example, many existing plasma‐sprayed HA coatings fall short in meeting the requirements of grain size and crystallinity, and as such are subject to enhanced resorption in body fluid. On the other hand, relatively poor interfacial bonding and stability is an obstacle to the application of the HA coatings in high load bearing Ti6Al4V knee joint implants. Here, we report on an alternative: a plasma‐assisted, concurrent, sputtering deposition technique for high performance biocompatible HA coatings on Ti6Al4V implant alloy. The plasma‐assisted RF magnetron co‐sputtering deposition method allows one to simultaneously achieve most of the desired attributes of the biomimetic material and overcome the aforementioned problems. This article details the film synthesis process specifications, extensive analytical characterization of the material's properties, mechanical testing, simulated body fluid assessments, biocompatibility and cytocompatibility of the HA‐coated Ti6Al4V orthopedic alloy. The means of optimization of the plasma and deposition process parameters to achieve the desired attributes and performance of the HA coating, as well as future challenges in clinical applications are also discussed.SEM image of differentiated cells on HA bioceramics deposited by plasma sputtering, after a two‐day incubation period.magnified imageSEM image of differentiated cells on HA bioceramics deposited by plasma sputtering, after a two‐day incubation period.

Microstructural evolution and strengthening mechanisms in Ti–Nb–Zr–Ta, Ti–Mo–Zr–Fe and Ti–15Mo biocompatible alloys

The microstructural evolution and the strengthening mechanisms in the two quaternary alloys, TNZT (Ti–34Nb–9Zr–8Ta) and TMZF (Ti–13Mo–7Zr–3Fe), and one binary alloy, Ti–15Mo, have been investigated. In the homogenized condition both the quaternary alloys exhibited a microstructure consisting primarily of a β Ti matrix with grain boundary α precipitates and a low volume fraction of primary α precipitates while the binary alloy showed single-phase microstructure with large β grains. On ageing the homogenized alloys at 600 °C for 4 h, all the alloys exhibited the precipitation of refined scale secondary α precipitates distributed homogeneously in the β matrix. However, after ageing while the hardness of TMZF marginally increased, that of the TNZT and Ti–15Mo alloys decreased. Furthermore, the modulus of TNZT decreased while other two alloys showed opposite trends. TEM studies indicate that there is initially a B2 ordering in TNZT that is destroyed after ageing causing a reduction in both hardness and modulus of this alloy. Also in Ti–15Mo, dissolution of ω precipitates on ageing causes the hardness to reduce, while the precipitation of secondary α causes an increase in the modulus. Using these examples, the important influence of thermal processing on the property–microstructure relationships in orthopaedic alloys for implant applications will be highlighted.

Tribological behaviour of plasma nitrided Ti-5Al-2Nb-1Ta alloy against UHMWPE

A detailed study has been made on the wear behaviour of untreated and plasma nitrided Ti-5Al-2Nb-1Ta orthopaedic alloy against ultra high molecular weight polyethylene (UHMWPE) using pin on disc tribometer under lubricated conditions. The effects of nitriding temperature and nitriding time on the basis of the evolution of the wear volume loss and friction coefficient were investigated. The wear resistance of the plasma nitrided alloys increased considerably when compared to the untreated alloy. The wear debris identified using X-ray diffraction measurements indicated the formation of titanium oxide and titanium oxynitride particles. The wear rate was found to increase with increase in load and sliding velocity.

Effect of N+ion implantation on the corrosion behaviour of Ti–6Al–7Nb and Ti–5Al–2Nb–1Ta orthopaedic alloys in Hanks solution

Ti—6Al—7Nb and Ti—5Al—2Nb—1Ta alloys were implanted with N+ ions with an ion energy of 75 keV at a dose rate of 1 × 1017 and 1 × 1018 ions cm−2. Open circuit potential (OCP) and potentiodynamic cyclic polarization measurements were carried out on the titanium alloys in Hanks solution to assess their corrosion resistance. The tendency for repassivation is higher in the case of implanted alloys than in untreated alloys owing to the formation of stable passive films. The impedance data showed a decrease in the double layer capacitance and an increase in the charge transfer resistance of the treated alloys. Nitrogen ion implanted Ti—6Al—7Nb was found to be more corrosion resistant than implanted Ti—5Al—2Nb—1Ta alloy.

Strengthening mechanisms in Ti–Nb–Zr–Ta and Ti–Mo–Zr–Fe orthopaedic alloys

The microstructural evolution and attendant strengthening mechanisms in two novel orthopaedic alloy systems, Ti–Nb–Zr–Ta and Ti–Mo–Zr–Fe, have been compared and contrasted in this paper. Specifically, the alloy compositions considered are Ti–34Nb–9Zr–8Ta and Ti–13Mo–7Zr–3Fe. In the homogenized condition, both alloys exhibited a microstructure consisting primarily of a β matrix with grain boundary α precipitates and a low-volume fraction of intra-granular α precipitates. On ageing the homogenized alloys at 600°C for 4 hr, both alloys exhibited the precipitation of refined scale secondary α precipitates homogeneously in the β matrix. However, while the hardness of the Ti–Mo–Zr–Fe alloy marginally increased, that of the Ti–Nb–Zr–Ta alloy decreased substantially as a result of the ageing treatment. In order to understand this difference in the mechanical properties after ageing, TEM studies have been carried out on both alloys prior to and post the ageing treatment. The results indicate the existence of a metastable B2 ordering in the Ti–Nb–Zr–Ta alloy in the homogenized condition which is destroyed by the ageing treatment, consequently leading to a decrease in the hardness.

Electrochemical behaviour and characterisation of plasma nitrided Ti–5Al–2Nb–1Ta orthopaedic alloy in Hanks solution

The present investigation deals with the study of the corrosion behaviour of glow discharge nitrided orthopaedic Ti–5Al–2Nb–1Ta alloy, using electrochemical techniques in Hanks solution. Potentiodynamic cyclic polarisation measurements show that the pit repassivation potential was higher in the case of nitrided alloy than the untreated alloy. The maximum pit repassivation potential was obtained for the alloy nitrided at 900 °C for 8 h. The electrochemical impedance spectroscopic (EIS) measurements showed an increased charge transfer resistance ( R ct) and decreased double layer capacitance ( C dl) for nitrided alloys.

Application of an interface failure model to predict fatigue crack growth in an implanted metallic femoral stem

A novel computational modelling technique has been developed for the prediction of crack growth in load bearing orthopaedic alloys subjected to fatigue loading. Elastic–plastic fracture mechanics has been used to define a three-dimensional fracture model, which explicitly models the opening, sliding and tearing process. This model consists of 3D nonlinear spring elements implemented in conjunction with a brittle material failure function, which is defined by the fracture energy for each nonlinear spring element. Thus, the fracture energy criterion is implicit in the brittle material failure function to search for crack initiation and crack development automatically. A degradation function is employed to reduce interfacial fracture properties corresponding to the number of cycles; thus fatigue lifetime can be predicted. Unlike other failure modelling methods, this model predicts the failure load, crack path and residual stiffness directly without assuming any pre-flaw condition. As an example, fatigue of a cobalt based alloy (CoCrMo) femoral stem is simulated. Experimental fatigue data was obtained from four point bending tests. The finite element model simulated a fully embedded implant with a constant point load. Comparison between the model and mechanical test results showed good agreement in fatigue crack growth rate.

Reactive Species in RF Plasma Sputtering Deposition of Nanocrystalline Calcium Phosphate Bio-Active Films

Optical emission of reactive plasma species during the synthesis of functionally graded calcium phosphate-based bioactive films has been investigated. The coatings have been deposited on Ti-6Al-4V orthopedic alloy by co-sputtering of hydroxyapatite (HA) and titanium targets in reactive plasmas of Ar + H2O gas mixtures. The species, responsible for the Ca-P-Ti film growth have been non-intrusively monitored in situ by a high-resolution optical emission spectroscopy (OES). It is revealed that the optical emission originating from CaO species dominates throughout the deposition process. The intensities of CaO, PO and CaPO species are strongly affected by variations of the operating pressure, applied RF power, and DC substrate bias. The optical emission intensity (OEI) of reaction species can efficiently be controlled by addition of H2O reactant.