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PubMed2006

The clinical significance of metal ion release from cobalt-chromium metal-on-metal hip joint arthroplasty.

Metal-on-metal (MOM) bearings offer extremely low wear and the avoidance of polyethylene but generate metallic wear particles. Although their total volume is dramatically smaller than polyethylene debris, these particles are in the nanometre size range and are many times more numerous. Metallic particles are ingested by macrophages or may be disseminated via lymphatics to the reticuloendothelial system. They corrode, and metal ions are present in the circulation and concentrated in erythrocytes. Excretion of metal ions via the kidneys seems to balance their generation in patients with MOM implants. However, highly sensitive detection methods can be used to show that levels of circulating cobalt and chromium ions are several times the normal level. These concentrations are well within the limits identified as dangerous to health in workers exposed to industrial chemicals, and also considerably lower than the levels found to cause cell toxicity in vitro. The local concentrations of particles and metal ions in the synovial tissue may occasionally exceed these limits and cause tissue necrosis. Clinical experience of lysis is rare in association with MOM bearings, as are hypersensitivity reactions and MOM bearings have had an excellent record over four decades and have a favourable benefit to risk ratio. Further reduction in risk will be achieved by improvement of materials, engineering, and accuracy of insertion.

Bone Neoplasms↗
PubMed1996

[The bonding mechanisms of base metals for metal-ceramic crown microstructure analysis of bonding agent and gold bond between porcelain and base metals].

The use of base metal alloys for porcelain fused to a metal crown and bridges has increased recently because of lower price, high hardness, high tensile strength and high elastic modulus. The addition of beryllium to base metal alloys increased fluidity and improved casting fitness. Beryllium also controlled surface oxidation and bonding strength. The bonding agent and gold bonding agent also affected the bonding strength between porcelain and metal alloys. Four commercially available ceramic base alloys were studied (two alloys contained beryllium element, another two did not). The purpose of this investigation was to study the microstructure between porcelain matrix, bonding agent and alloy matrix interfaces. A scanning electron micro-probe analyzer and energy dispersive X-ray spectroscopy (EDXS) were used to study the distribution of elements (Ni, Cr, Mo, Cu, O, Si, Sn, Al) in four base alloys. The following results were obtained: 1. The thickness of the oxidized layer of Rexillium III alloy and Unitbond alloy (contained beryllium) was thinner than Unibond alloy and Wiron 88 alloy (no beryllium). 2. The thickness of the oxidized layer of alloys in air (10 minutes and 30 minutes) was thinner in Unitbond (2.45 microns and 3.80 microns) and thicker in Wiron 88 (4.39 microns and 5.96 microns). 3. The thickness of the oxidized layer occurring for a duration of ten minutes (in vaccum) showed that the Rexillium III alloy was the thinnest (1.93 microns), and Wiron 88 alloy was the thickest (2.30 microns). But in thirty minutes (vacuum), Unitbond alloy was the thinnest (3.37 microns), and Wiron 88 alloy was the thickest (5.51 microns). 4. The intensity of Cr elements was increased obviously near the interface between Unitbond alloy, Wiron 88 alloy (no beryllium) and oxidized layer, but the intensity of Ni and Mo elements was slightly increased. The intensity of Cr element was not increased markedly between Rexillium III alloy, Unitbond alloy (beryllium) and oxidized layer. 5. A white-grayish oxidized layer appeared at the metal-ceramic interfaces but the thickness of oxidized layer was not obviously different. 6. The use of bonding agent at metal-ceramic interface leads to the deposition of many Sn elements at about 40 microns range within the porcelain surface. 7. Second interaction phases at the porcelain layer appeared when gold bonding agent was used, and a 50-100 microns microleakage occurred at the metal-ceramic interface.

Dental Bonding↗
PubMed2004

Steady-state elastohydrodynamic lubrication analysis of a metal-on-metal hip implant employing a metallic cup with an ultra-high molecular weight polyethylene backing.

The elastohydrodynamic lubrication (EHL) analysis was carried out in this study for a 28 mm diameter metal-on-metal hip prosthesis employing a metallic cup with an ultra-high molecular weight polyethylene (UHMWPE) backing under a simple steady state rotation representing the flexion/extension during walking. Both Reynolds and elasticity equations were coupled and solved numerically by the finite difference method. The elastic deformation was determined by means of the fast Fourier transform (FFT) technique using the displacement coefficients obtained from the finite element method. Excellent agreement of the predicted elastic deformation was obtained between the FFT technique and the conventional direct summation method. The number of grid points used in the lubrication analysis was found to be important in predicting accurate film thicknesses, particularly at low viscosities representative of physiological lubricants. The effect of the clearance between the femoral head and the acetabular cup on the predicted lubricant film thickness was shown to be significant, while the effect of load was found to be negligible. Overall, the UHMWPE backing was found not only to reduce the contact pressure as identified in a previous study by the authors (Liu et al., 2003) but also significantly to increase the lubricant film thickness for the 28 mm diameter metal-on-metal hip implant, as compared with a metallic mono-block cup.

Computer Simulation↗
PubMed1990

[Hard metal-induced lung changes. Hard metal asthma--interstitial hard metal pneumopathy].

Hard metal pneumopathy and hard metal asthma are two separate forms of hard metal lung disease. Cobalt is the probable causal agent involved. Bronchial provocation with hard metal powder induces obstruction within 2 hours of the challenge. Suspected hard metal pneumopathy, however, should be confirmed or excluded by a period of non-exposure followed by re-exposure, since the long-term exposure in patients suffering from hard-metal pneumopathy leads to pulmonary fibrosis.

Adult↗
PubMed2002

Solid-phase extraction for the decontamination of alkali metal, alkaline Earth metal, and ammonium salts from heavy metal ions.

Salicylaldoxime-immobilized silica gel was characterized and used as a potential sorbent for heavy metal ions, viz. Cu(II), Ni(II), Co(II), and Zn(II). The experimental conditions were optimized both in batch and column processes to achieve the maximum efficiency. Kinetic and thermodynamic parameters as well as isotherm constants were evaluated to test the feasibility of the process. The role of various metal ions and different anions were tested in order to monitor the process in case of real samples. The alkali metal, alkaline earth metal, and ammonium salts do not have any effect on the said process. This differential behavior can be effectively used for the decontamination of alkali metal, alkaline earth metal, and ammonium salts from Cu(II), Ni(II), Co(II), and Zn(II) ions via solid phase extraction following AAS measurement. The purification of the salts was confirmed by voltammetric experiment.

Journal Article↗
PubMed2004

Formation and reactions of metal-metal bonded heterobimetallic (C5H4PR2)-bridged (Zr-Ir) and (Zr-Rh) complexes: evidence for the participation of metal hydride intermediates.

Treatment of the complexes [(C(5)H(4)PR(2))(2)Zr(CH(3))(2)](b: R = isopropyl; c: R = cyclohexyl) with the reagent HIr(CO)(PPh(3))(3) (2b) yield the heterobimetallic complexes [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Ir(CO)(PPh(3)))] (4b, 4c) with evolution of methane. The reaction of the -PPh(2) substituted analogue with initially yields an intermediate [(H(3)C)(2)Zr(mu-C(5)H(4)PPh(2))(2)Ir(H)(CO)(PPh(3))] 5a, that still contains both methyl groups at zirconium and does not contain a metal-metal bond. At room temperature, the intermediate reacts further with methane formation to eventually yield the (Zr-Ir) complex 4a. The corresponding [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Rh(CO)(PPh(3)))] complexes 3a (R = Ph) and 3b (R = isopropyl) react cleanly with isopropyl alcohol to liberate methane and yield the corresponding [mu-C(5)H(4)PR(2))(2)(Me(2)CHO-Zr-Rh(CO)(PPh(3)))] products (7a, 7b). Carefully monitoring the reaction of with Me(2)CHOH by NMR revealed that the Zr-Rh functionality is attacked first to give the intermediate [Me(Me(2)CHO)Zr([micro sign]-C(5)H(4)PR(2))(2)Rh(H)(CO)(PPh(3))] (6b). This intermediate then reacts further to cleave off methane and re-form the (Zr-Rh) metal-metal bond to yield the product 7b. The tetrametallic mu-oxo-(Zr-Rh) metallocene derivate 11a was obtained starting from the (Zr-Rh) complex 3a and it was characterized by X-ray diffraction. It may be that this reaction is also initiated by H-OH addition to the [Zr-Rh] metal-metal bond.

Journal Article↗
PubMed2004

The functional role of the binuclear metal center in D-aminoacylase: one-metal activation and second-metal attenuation.

Our structural comparison of the TIM barrel metal-dependent hydrolase(-like) superfamily suggests a classification of their divergent active sites into four types: alphabeta-binuclear, alpha-mononuclear, beta-mononuclear, and metal-independent subsets. The d-aminoacylase from Alcaligenes faecalis DA1 belongs to the beta-mononuclear subset due to the fact that the catalytically essential Zn(2+) is tightly bound at the beta site with coordination by Cys(96), His(220), and His(250), even though it possesses a binuclear active site with a weak alpha binding site. Additional Zn(2+), Cd(2+), and Cu(2+), but not Ni(2+), Co(2+), Mg(2+), Mn(2+), and Ca(2+), can inhibit enzyme activity. Crystal structures of these metal derivatives show that Zn(2+) and Cd(2+) bind at the alpha(1) subsite ligated by His(67), His(69), and Asp(366), while Cu(2+) at the alpha(2) subsite is chelated by His(67), His(69) and Cys(96). Unexpectedly, the crystal structure of the inactive H220A mutant displays that the endogenous Zn(2+) shifts to the alpha(3) subsite coordinated by His(67), His(69), Cys(96), and Asp(366), revealing that elimination of the beta site changes the coordination geometry of the alpha ion with an enhanced affinity. Kinetic studies of the metal ligand mutants such as C96D indicate the uniqueness of the unusual bridging cysteine and its involvement in catalysis. Therefore, the two metal-binding sites in the d-aminoacylase are interactive with partially mutual exclusion, thus resulting in widely different affinities for the activation/attenuation mechanism, in which the enzyme is activated by the metal ion at the beta site, but inhibited by the subsequent binding of the second ion at the alpha site.

Amidohydrolases↗
PubMed1993

How the anti-(metal chelate) antibody CHA255 is specific for the metal ion of its antigen: X-ray structures for two Fab'/hapten complexes with different metals in the chelate.

Antibodies with bound metal-chelate haptens provide new means for exploiting the diverse properties of metallic elements. The murine monoclonal antibody CHA255 (IgG1 lambda) binds the metal-chelate hapten indium (III)-4-[N'-(2-hydroxyethyl)thioureido]-L-benzyl-EDTA (designated In-EOTUBE) with high affinity (K(a) = 1.1 x 10(10) M-1). Antibody binding is highly specific for the indium chelate; the affinity decreases as much as 10(4) with other metals, even those having ionic radii close to indium. To better understand this selectivity, the crystal structure of the antigen-binding fragment (Fab') of CHA255 complexed with its hapten, In(III)-EOTUBE, was determined by molecular replacement and refined at 2.2-A resolution. The structure of CHA255 Fab' complexed with Fe(III)-EOTUBE was also determined and refined at 2.8-A resolution. In both structures, the hapten's EDTA moiety is half-buried near the center of the complementarity-determining regions (CDR's). Five of the six CDR's on the Fab' interact with the hapten through protein side-chain atoms (but not main-chain atoms). A novel feature of the In-EOTUBE/Fab' complex is coordination of the indium by N epsilon of one histidine from the heavy chain's third CDR (distance = 2.4 A). The histidine coordination is not observed in the Fe-EOTUBE/Fab' complex, due mainly to a slightly different hapten conformation that reduces metal accessibility; this may partially explain the 20-fold lower affinity of CHA255 for iron hapten. An unexpected feature of the Fab' overall is an elbow angle of 193 degrees (the angle between the pseudodyad axes of the Fab's constant and variable domains).

Amino Acid Sequence↗
PubMedDate not supplied

Bonding indirect resin composites to metal: Part 1. Comparison of shear bond strengths between different metal-resin bonding systems and a metal-ceramic system.

PURPOSE: This laboratory study compared the shear bond strength between three indirect resin composites and a noble alloy using their respective bonding systems. MATERIALS AND METHODS: One hundred twenty disks cast in a medium-gold, high-noble metal-ceramic alloy (V-Deltaloy) were divided equally into four groups and received different treatments for veneering: Conventional feldspathic porcelain (Omega) was applied on one set of specimens to be used as a control, and three indirect resin composites (Artglass, Sculpture, Targis) with their respective bonding systems were used for the other groups. The specimens were tested in a parallel shear test, half of them after 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling. The fractured specimens were evaluated to determine the nature of the failure. RESULTS: The mean shear bond strength values (in MPa), before and after wet storage and thermocycling, were 30 and 23 for the metal-ceramic group, 29 and 23 for the Artglass group, 20 and 19 for the Sculpture group, and 17 and 14 for the Targis group, respectively. The metal-ceramic and Artglass groups exhibited significantly higher bond strengths than the other two groups. All specimens, with the exception of the Sculpture group, showed a significant decrease in bond strength after wet storage and thermocycling. CONCLUSION: No group exceeded the shear bond strength of the metal-ceramic group, but the Artglass group with its respective metal-resin bonding system exhibited similar bond strengths. The Sculpture group showed a stable bond after water storage and thermocycling.

Aluminum Silicates↗
PubMed1996

The impact of heavy metals on the grey garden slug, Deroceras reticulatum (Müller): Metal storage, cellular effects and semi-quantitative evaluation of metal toxicity.

Laboratory-reared grey garden slugs, Deroceras reticulatum, were exposed to soil and food treated with solutions of three metal salts (CdCl2, ZnCl2, PbCl2) in three environmentally relevant concentrations, each for 21 days. Metal concentrations were determined in the soil, food and slugs by atomic absorption spectrophotometry (AAS). Zinc was localized ultrastructurally in the hepatopancreatic cells by means of energy-filtering transmission electron microscopy (EFTEM). Zinc, and also high amounts of copper, could be detected by electron spectroscopical imaging (ESI) and electron energy loss spectroscopy (EELS) in spherites of the basophilic cells. Ultrastructural responses to metal impact were investigated in two cell types of the hepatopancreas (digestive and basophilic cells) and the cellular responses were found to be dose- and metal-dependent. In order to evaluate the toxicity of the respective metal concentrations to the slugs, the ultrastructural reactions were semi-quantified and summarized as complex reaction patterns of numerous organelles. This novel approach provides a basis for the use of data from standardized tests as a background for risk assessment studies in the field.

Journal Article↗
PubMed2002

Metal-hydride bond activation and metal-metal interaction in dinuclear iron complexes with linking dinitriles: a synthetic, electrochemical, and theoretical study.

The dinuclear iron(II)-hydride complexes [[FeH(dppe)(2)](2)(mu-LL)][BF(4)](2) (LL = NCCH=CHCN (1a), NCC(6)H(4)CN (1b), NCCH(2)CH(2)CN (1c); dppe = Ph(2)PCH(2)CH(2)PPh(2)) and the corresponding mononuclear ones, trans-[FeH(LL)(dppe)(2)][BF(4)] (2a-c) were prepared by treatment of trans-[FeHCl(dppe)(2)], in tetrahydrofuran (thf) and in the presence of Tl[BF(4)], with the appropriate dinitrile (in molar deficiency or excess, respectively). Metal-metal interaction was detected by cyclic voltammetry for 1a, which, upon single-electron reversible oxidation, forms the mixed valent Fe(II)/Fe(III) 1a(+) complex. The latter either undergoes heterolytic Fe-H bond cleavage (loss of H(+)) or further oxidation, at a higher potential, also followed by hydride-proton evolution, according to ECECE or EECECEC mechanistic processes, respectively, which were established by digital simulation. Anodically induced Fe-H bond rupture was also observed for the other complexes and the detailed electrochemical behavior, as well as the metal-metal interaction (for 1a), were rationalized by ab initio calculations for model compounds and oxidized derivatives. These calculations were used to generate the structural parameters (full geometry optimization), the most stable isomeric forms, the ionization potentials, the effective atomic charges, and the molecular orbital diagrams, as well as to predict the nature of the other electron-transfer induced chemical steps, i.e. geometric isomerization and nucleophilic addition, by BF(4)(-), to the unsaturated iron center resulting from hydride-proton loss. From the values of the oxidation potential of the complexes, the electrochemical P(L) and E(L) ligand parameters were also estimated for the dinitrile ligands (LL) and for their mononuclear complexes 2 considered as ligands toward a second binding metal center.

Journal Article↗
PubMed2005

The release of metals from metal-on-metal surface arthroplasty of the hip.

The aim of the study was to evaluate the serum and urine levels of cobalt (Co), chromium (Cr), manganese (Mn), molybdenum (Mo) and nickel (Ni) in patients who had undergone metal-on-metal hybrid surface arthroplasties on the supposition that a release of metals would occur due to the large head size of this type of implant. Metal levels were determined by using an analytical method based on sector field inductively coupled plasma mass spectrometry. Results showed a significant difference between patients and control subjects in mean levels of Co and Cr in serum (p<0.0001 and p=0.02, respectively) and in urine (p<0.0001 for both). No significant differences were observed in mean serum and urinary levels of Mn, Mo and Ni. Although the clinical consequences of these changes, if any, are unknown, further studies could be performed in a larger number of subjects implanted with a total surface arthroplasty at follow-up times over different periods.

Adult↗
PubMed2000

The geometry of metal-ligand interactions relevant to proteins. II. Angles at the metal atom, additional weak metal-donor interactions.

Geometrical data which could be of relevance in the structure determination, structure refinement, assessment or understanding of metalloproteins have been extracted from the Cambridge Structural Database (CSD). The CSD contains crystallographic data from 'small-molecule' structures determined by X-ray or neutron diffraction to an accuracy and precision much better than that of most current protein structure determinations. Structures of Mg, Mn, Fe, Cu and Zn complexes with ligands whose donor atoms may be only N, O, S or Cl have been selected and analysed in terms of the geometry of the metal coordination group - octahedral, tetrahedral, tetragonal pyramidal etc. The r.m.s. deviation of all the interbond angles around the metal atom provides a measure, delta, of the deviation from ideal geometry. Average values of delta are tabulated for the different metals in each type of complex. For simple non-chelated complexes of Mn, Fe and Zn, distortions of up to 5 degrees in octahedral complexes and 10 degrees in tetrahedral complexes are found to be normal and seem likely to be a consequence of packing effects, ligand bulk or intramolecular effects. Substantially larger distortions are found for some other metals and geometries and are common for chelated complexes. Brief comments on six-, seven- and eight-coordinate Ca complexes are included. Tables are also presented showing that for four- and five-coordinate complexes of Zn and Cu it is quite common to find additional weakly coordinated ligands, usually with N or O donor atoms and with M.N,O distances longer than a normal bond length but shorter than a van der Waals contact, e.g. in the range 2.4-3.0 A for Zn and 2.6-3.0 A for Cu. Although the contributions to bond valency or bonding energy of such interactions may not be great, their effect on geometry can be considerable; they can, for example, cause much larger distortions of tetrahedral Zn complexes than indicated above.

Chelating Agents↗
PubMed2003

Contact mechanics of metal-on-metal hip implants employing a metallic cup with a UHMWPE backing.

The contact mechanics in metal-on-metal hip implants employing a cobalt chromium acetabular cup with an ultra-high molecular weight polyethylene (UHMWPE) backing were analysed in the present study using the finite element method. A general modelling methodology was developed to examine the effects of the interfacial boundary conditions between the UHMWPE backing and a titanium shell for cementless fixation, the coefficient of friction and the loading angle on the predicted contact pressure distribution at the articulating surfaces. It was found that the contact mechanics at the bearing surfaces were significantly affected by the UHMWPE backing. Consequently, a relatively constant pressure distribution was predicted within the contact conjunction, and the maximum contact pressure occurred towards the edge of the contact. On the other hand, the interfacial boundary condition between the UHMWPE backing and the titanium shell, the coefficient of friction and the loading angle were found to have a negligible effect on the contact mechanics at the bearing surfaces. Overall, the magnitude of the contact pressure was significantly reduced, compared with a similar cup without the UHMWPE backing. The importance of the UHMWPE backing on the tribological performance of metal-on-metal hip implants is discussed.

Chromium Alloys↗
PubMed1997

Clinical wear behaviour of ultra-high molecular weight polyethylene cups paired with metal and ceramic ball heads in comparison to metal-on-metal pairings of hip joint replacements.

In the course of 30 years of hip endoprosthetics, a number of material combinations for the cups and balls of total hip prostheses have proven successful under clinical conditions. Favourably priced hip prostheses with polyethylene cups and metal balls are available for older patients with a moderate range of activity. Polyethylene wear of 100-300 microns/year is to be expected with these models. Ceramic balls (aluminium oxide for diameters 32 and 28 mm and zirconium oxide for 22 mm) paired with polyethylene cups are recommended for patients with a life expectancy of 10 to 20 years, because the expected polyethylene wear rate with this material combination is only 50-150 microns/year. In other words, the life cycle of the polyethylene cup is doubled, when it is paired with a ceramic ball. A similar polyethylene wear rate is also to be expected with oxygen-deep-hardened TiAlNb metal balls, which are currently the subject of a clinical field study. Last but not least, CoCrMoC metal-metal and Al2O3 ceramic ceramic pairings, which have the lowest wear rate of 2-20 microns/year, are available for highly active patients with a life expectancy of more than 20 years. As far as the cup-ball pairing is concerned and under the current pressure of costs, the surgeon should be able to select the optimum hip prosthesis model for every patient from these three categories.

Alloys↗
PubMed2003

Levels of metal ions after small- and large-diameter metal-on-metal hip arthroplasty.

Metal-on-metal (MOM) bearings for hip arthroplasty are increasing in popularity. Concern remains, however, regarding the potential toxicological effects of the metal ions which these bearings release. The serum levels of cobalt and chromium in 22 patients who had undergone MOM resurfacing arthroplasty were compared with a matched group of 22 patients who had undergone 28 mm MOM total hip arthroplasty (THA). At a median of 16 months (7 to 56) after resurfacing arthroplasty, we found the median serum levels of cobalt and chromium to be 38 nmol/l (14 to 44) and 53 nmol/l (23 to 165) respectively. These were significantly greater than the levels after 28 mm MOM THA which were 22 nmol/l (15 to 87, p = 0.021) and 19 nmol/l (2 to 58, p < 0.001) respectively. Since the upper limit for normal patients without implants is typically 5 nmol/l, both groups had significantly raised levels of metal ions. MOM bearings of large diameter, however, result in a greater systemic exposure of cobalt and chromium ions than bearings of small diameter. This may be of relevance for potential long-term side-effects. It is not known to what extent this difference is due to corrosion of the surfaces of the component or of the wear particles produced.

Adult↗