SEARCH · Search PubMed

Results for “ZIRCONIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources

PubMed2002

Mechanical performance of acrylic bone cements containing different radiopacifying agents.

The effect that three different radiopacifying agents, two of them inorganic (BaSO4, ZrO2) and one organic (an iodine containing monomer, IHQM) have on the static and dynamic mechanical properties of acrylic bone cements was studied. Compressive and tensile strength, fracture toughness and fatigue crack propagation were evaluated. The effect of the inorganic fillers depends on their size and morphology. In relation to the radiolucent cement, the addition of zirconium dioxide improved significantly the tensile strength, the fracture toughness and the fatigue crack propagation resistance. In contrast, the addition of barium sulphate produced a decrease of the tensile strength, but did not affect the fracture toughness and improved the crack propagation resistance. When the iodine containing monomer was used, although the tensile strength and the fracture toughness increased, the fatigue crack propagation resistance remained as low as it was for the radiolucent cement.

Barium Sulfate↗

PubMed1997

Wear characteristics of ceramic-on-ceramic for hip endoprostheses.

Femoral ball heads of aluminium oxide or zirconium oxide ceramics are used for total hip replacement. This application is based on their attractive tribological properties. Standard and state-of-the-art are femoral ball heads made of alumina (Al2O3) articulating against acetabular cups of polyethylene (PE-UHMW) and zirconia (Y-TZP) heads articulating against polyethylene cups. A very attractive wear couple is ceramic-on-ceramic. Some of the various ceramic combinations have been tested using the ring-on-disc method according to ISO 6474. The combination alumina/alumina was found to produce extremely low wear; catastrophic wear was found for the combinations alumina/Y-TZP and Y-TZP/Y-TZP.

Aluminum Oxide↗

PubMed1990

Comparative investigations of regional lymph nodes and pseudocapsules after implantation of joint endoprostheses.

Morphological alterations of pseudocapsules and regional lymph nodes were studied by light and electron microscopy and by Laser Microprobe Mass Analysis (LAMMA). The tissue specimens originated from 32 autopsies of patients with hip joint endoprostheses (time in situ: 3 weeks - 15 years, average: 6 years) and two cases with knee joint endoprostheses. Characteristic changes of the lymph nodes as well as of the pseudocapsules consisted in an infiltration by monocytic histiocytes with various intracytoplasmatic wear particles. The foreign material consisted mainly of the components of bone cement: polymethylmethacrylate (PMMA) and zirconium oxide, to a lesser degree of polyethylene from the articulating surfaces. In two cases with special types of prostheses ceramic or metallic wear particles could be detected too. Most of the wear particles were found in the ipsilateral parailiac lymph nodes and in the paraaortic lymph nodes bilaterally. In the cases with mostly stable prostheses small amounts of wear particles were found in the lymph nodes as soon as 1.5 years after insertion and their number increased in all groups of lymph nodes after longer duration of the implant. The phagocytosing histiocytes showed degenerative changes. At present it is not clear, if the cell damage is caused by the amount of phagocytosed wear particles alone or if specific toxic effects of certain substances are of importance.

Granulation Tissue↗

PubMed2002

Titanium particles suppress expression of osteoblastic phenotype in human mesenchymal stem cells.

Long-term stability of arthroplasty prosthesis depends on the integration between osseous tissue and the implant biomaterial. Integrity of the osseous tissue requires the contribution of mesenchymal stem cells and their continuous differentiation into an osteoblastic phenotype. This study aims to investigate the hypothesis that exposure to wear debris particles derived from orthopaedic biomaterials affects the osteoblastic differentiation of human mesenchymal stem cells (hMSC). Upon in vitro culture in the presence of osteogenic supplements (OS), we observe that cultures of hMSCs isolated from femoral head bone marrow are capable of osteogenic differentiation, expressing alkaline phosphatase, osteocalcin, and bone sialoprotein (BSP), in addition to producing collagen type I and BSP accompanied by extracellular matrix mineralization. Exposure of OS-treated hMSCs to submicron commercially pure titanium (cpTi) particles suppresses BSP gene expression, reduces collagen type I and BSP production, decreases cellular proliferation and viability, and inhibits matrix mineralization. In comparison, exposure to zirconium oxide (ZrO2) particles of similar size did not alter osteoblastic gene expression and resulted in only a moderate decrease in cellular proliferation and mineralization. Confocal imaging of cpTi-treated hMSC cultures revealed patchy groups of cells displaying disorganized cytoskeletal architecture and low levels of extracellular BSP. These in vitro findings suggest that chronic exposure of marrow cells to titanium wear debris in vivo may contribute to decreased bone formation at the bone/implant interface by reducing the population of viable hMSCs and compromising their differentiation into functional osteoblasts. Understanding the nature of hMSC bioreactivity to orthopaedic wear debris should provide additional insights into mechanisms underlying aseptic loosening.

Alkaline Phosphatase↗

PubMed2003

Direct and indirect induction of apoptosis in human mesenchymal stem cells in response to titanium particles.

The most frequent complication of total joint arthroplasty is periprosthetic osteolysis initiated by an inflammatory response to orthopaedic wear debris, which if left untreated, can result in implant instability and failure, eventually requiring revision surgery. We have previously reported that osteogenic differentiation of human marrow stroma-derived mesenchymal stem cells (hMSCs) is suppressed upon exposure to titanium particles, accompanied by reduced bone sialoprotein (BSP) gene expression, diminished production of collagen type I and BSP, decreased cellular viability and proliferation, and inhibition of extracellular matrix mineralization. In this study, we have further investigated hMSC cytotoxicity upon exposure to submicron particles of commercially pure titanium (cpTi) and zirconium oxide (ZrO(2)). Our results showed that direct exposure to cpTi and ZrO(2) particles compromises cell viability through the induction of apoptosis, eliciting increased levels of the tumor suppressor proteins p53 and p73, in a manner dependent on material composition, particle dosage, and time. Additionally, conditioned medium collected from hMSCs exposed to cpTi particles, but not to ZrO(2) particles, is cytotoxic to hMSCs, inducing apoptosis in the absence of particles. These findings demonstrate that exposure to orthopaedically derived wear particles can compromise hMSC viability through the direct and indirect induction of apoptosis. Thus, prolonged in vivo exposure of marrow-derived hMSCs to implant-derived wear debris is likely to reduce the population of viable osteoprogenitor cells, and may contribute to poor periprosthetic bone quality and implant loosening.

Apoptosis↗

PubMed1989

A comparative experimental investigation in monkeys between three different implant materials.

To study the tissue integration of 2 new potential biomaterials (whisker silicon carbide, reinforced aluminum oxide, and zirconium oxide strengthened aluminium oxide) a comparative investigation between these ceramic materials and unalloyed titanium was performed on monkeys. Cylindrical implants (4 x 6 mm) were inserted in the femur of 10 adult monkeys. After observation periods ranging from 1 to 8 months the animals were killed and clinical and histological evaluations (microradiography and light-microscopy) were carried out. After 6-8 months, the implants were covered with bone and firmly attached, indicating an uneventful healing. Histologically, a close connection between bone and implant was observed. At some areas the implants were totally osseointegrated and at some areas there were soft tissue layers between implant and bone. No differences in bone repair with regard to the different materials could be observed.

Aluminum↗

PubMed1993

Monochromatic x-ray radiation for high resolution radiography in osteology.

The contrast of an x-ray exposure is influenced by the x-ray absorption of the examined material and the x-ray frequency. The examination of the absorbing properties of bone material in the molybdenum spectrum by means of the Bragg-method revealed an intense increase of absorption in the long-wave range. By using a zirconium filter, long-wave and monochromatic MoK alpha-rays can be isolated from the spectrum of a molybdenum x-ray tube. The x-ray exposures of thin bone tissue produced in this spectral range show a much greater degree of contrast and depth as compared to conventional exposures.

Alpha Particles↗

PubMed2003

Radiochemical separation of carrier-free 204,206 Bi from alpha-irradiated thallium oxide target.

Alpha activation of Tl(2)O(3) target results in the formation of carrier-free 204,206 Bi. Two different radiochemical methods were used for the separation of bismuth radionuclides from the target matrix. A very high separation factor was achieved using liquid-liquid extraction (LLX) method with methyl isobutyl ketone (MIBK)-HCl system. Solid-liquid exchange adsorption was carried out using a novel inorganic ion exchanger, zirconium vanadate from HCl medium. The separation was found to be maximum around pH 2.

Adsorption↗

PubMed1994

Easily regenerable affinity chromatographic zirconia-based support with concanavalin A as a model ligand.

The goal of this work was to develop a generic approach for producing affinity chromatographic columns which can be regenerated. Concanavalin A (Con A) was immobilized adsorptively by an in situ method onto a zirconium dioxide (zirconia) chromatographic support and used to resolve chromophorically labeled monosaccharides. The Con A was then removed from the zirconia by flushing with base. The same column was regenerated by applying a fresh aliquot of Con A. This cycle was repeated several times to demonstrate consistency in the loading capacity and the stability of the underlying zirconia support. Finally we used glutaraldehyde to cross-link the Con A to increase the long-term stability of the column. Hydrolyzing the protein with acid allowed it to be removed under alkaline conditions and the column regenerated simply by adding more Con A followed by glutaraldehyde cross-linking.

Adsorption↗

PubMed1998

Chromatographic characterization of phosphonate analog EDTA-modified zirconia support for biochromatographic applications.

Zirconium dioxide (zirconia) has a great affinity for inorganic and organic phosphate. Previous work from this laboratory demonstrated the utility of phosphate-modified microparticulate zirconia as a support for protein separations. We have extended this investigation to include the study of ethylenediamine-N,N'-tetramethylphosphonic acid (EDTPA), a phosphonate analog of EDTA, as a surface modifier for zirconia. Our work explores the use of EDTPA-modified zirconia (PEZ) for its potential use as a high-performance inorganic cation-exchange support for the separation of proteins. The phosphate groups in EDTPA very effectively block the sites responsible for strong interactions of hard Lewis bases with zirconia's surface. Modification of zirconia with EDTPA provides a "biocompatible" stationary phase, resulting in high mass recoveries of proteins. We compare PEZ with inorganic phosphate-modified zirconia to show increased efficiency, as well as unique selectivities for chromatography of proteins on the chelator-modified surface. Finally, the selectivity, efficiency, and separation mechanism are reported. The studies show that PEZ is a useful high-performance ion-exchange support for the separation of cationic proteins and for modulating the sites responsible for the high affinity of zirconia toward certain classes of anions.

Adsorption↗

PubMed2003

Mechanism of high-temperature CO2 sorption on lithium zirconate.

Lithium zirconate (Li2ZrO3) is one of the most promising materials for CO2 separation from flue gas at high temperature. This material is known to be able to absorb a large amount of CO2 at around 400-700 degrees C. However, the mechanism of the CO2 sorption/desorption process on Li2ZrO3 is not known yet. In this study, we examined the CO2 sorption/desorption mechanism on Li2ZrO3 by analyzing the phase and microstructure change of Li2ZrO3 during the CO2 sorption/desorption process with the help of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. Li2ZrO3 powders were prepared from lithium carbonate (Li2CO3) and zirconium oxide (ZrO2) by the solid-state method, and the CO2 sorption/desorption property was examined by TGA. It was shown that pure Li2ZrO3 absorbs a large amount of CO2 at high temperature with a slow sorption rate. Addition of potassium carbonate (K2CO3) and Li2CO3 in the Li2ZrO3 remarkably improves the CO2 sorption rate of the Li2ZrO3 materials. DSC analysis for the CO2 sorption process indicates that doped lithium/potassium carbonate is in the liquid state during the CO2 sorption process and plays an important role in improving the CO2 uptake rate. XRD analysis for phase and structure change during the sorption/desorption process shows that the reaction between Li2ZrO3 and CO2 is reversible. Considering all data obtained in this study, we proposed a double-shell model to describe the mechanism of the CO2 sorption/desorption on both pure and modified Li2ZrO3.

Adsorption↗

PubMed2003

Mechanisms of allene stereoinversion by imidozirconium complexes.

The zirconium-mediated stereoinversion of allenes has been investigated by studying the stereochemical behavior of metallacycles derived from [2 + 2] cycloaddition of enantioenriched allenes with chiral and achiral imidozirconocene complexes. Relative rates of metallacycle racemization were measured by circular dichroism, and intermediates in the selective stereoinversion of diphenylallene with a chiral imidozirconium complex were observed by NMR spectroscopy. Metallacycles derived from dialkylallenes are proposed to racemize via reversible beta-hydride elimination. Stereoinversion of diarylallene-derived metallacycles proceeds much more slowly and is thought to proceed through an eta4-azatrimethylenemethane transition state.

Alkadienes↗

PubMed2004

Cross-couplings of alkyl electrophiles under "ligandless" conditions: Negishi reactions of organozirconium reagents.

This report establishes that simple, "ligandless" palladium complexes can catalyze the first zirconium-Negishi reactions of alkyl electrophiles. In view of the attractiveness of ligandless catalysts (cost, simplicity, and ease of purification), these observations add a significant and intriguing new dimension to the development of effective palladium-based processes for coupling alkyl electrophiles.

Alkenes↗

PubMed2004

Catalytic enantio- and diastereoselective aldol reactions of glycine-derived silicon enolate with aldehydes: an efficient approach to the asymmetric synthesis of anti-beta-hydroxy-alpha-amino acid derivatives.

We have developed an efficient method for the asymmetric synthesis of anti-beta-hydroxy-alpha-amino acid derivatives based on highly enantio- and diastereoselective aldol reactions of the silicon enolate derived from N-trifluoroacetylglycinate with aldehydes using a chiral zirconium catalyst. The resulting N-trifluoroacetyl group is easily cleaved under either acidic or basic conditions and can be used directly as a protecting group for further transformations.

Aldehydes↗

PubMed2005

Catalytic ester-amide exchange using group (IV) metal alkoxide-activator complexes.

A process for preparation of amides from unactivated esters and amines has been developed using a catalytic system comprised of group (IV) metal alkoxides in conjunction with additives including 1-hydroxy-7-azabenzotriazole (HOAt). In general, ester-amide exchange proceeds using a variety of structurally diverse esters and amines without azeotropic reflux to remove the alcohol byproduct. Initial mechanistic studies on the Zr(Ot-Bu)4-HOAt system revealed that the active catalyst is a novel, dimeric zirconium complex as determined by X-ray crystallography.

Amides↗

PubMed2006

Efficient transamidation of primary carboxamides by in situ activation with N,N-dialkylformamide dimethyl acetals.

Two protocols for the transamidation of primary amides with primary and secondary amines, forming secondary and tertiary amides, respectively, are described. Both processes employ N,N-dialkylformamide dimethyl acetals for primary amide activation, producing N'-acyl-N,N-dialkylformamidines as intermediates, as widely documented in the literature. Although the latter intermediates react irreversibly with amines by amidinyl transfer, we show that in the presence of certain Lewis acid additives efficient acyl transfer occurs, providing new and useful methods for amide exchange. In one protocol for transamidation, the N'-acyl-N,N-dialkylformamidine intermediates are purified by flash-column chromatography and the purified intermediates are then treated with an amine (typically, 2.5 equiv) in the presence of scandium triflate (10 mol %) in ether to form in high yields the products of transamidation. In a second procedure, N'-acyl-N,N-dialkylformamidines are generated in situ and, without isolation, are subjected to transamidation in the presence of zirconium chloride (0.5 equiv) and an amine (typically 2 equiv). A variety of different primary amides and amines are found to undergo efficient transamidation using the methods described.

Acetals↗

PubMed2003

Synthesis of (+)-manoalide via a copper(I)-mediated 1,2-metalate rearrangement.

An enantiospecific synthesis of the phospholipase A(2) inhibitor (+)-(4R)-manoalide is reported in which all 25 carbons of the sesterterpenoid skeleton are constructed from 3-furaldehyde, trimethylalane, oxirane, CO, beta-ionone, and propargyl bromide. The overall yield for the longest linear sequence (12 steps) is 12%. Key steps include (a) a zirconium-catalyzed carboalumination reaction to construct the C10-C11 trisubstituted alkene, (b) a Cu(I)-mediated 1,2-metalate rearrangement to construct the C6-C7 trisubstituted alkene, (c) a Sharpless kinetic resolution to secure the (4R)-stereochemistry, (d) generation of a 5-stannyl-2,3-dihydrofuran by Mo-catalyzed cycloisomerization of a homopropargylic alcohol, and (e) construction of the hydroxyfuranone ring by photooxidation of a silylfuran.

Alkenes↗

PubMed2005

A facile Zr-mediated approach to (Z)-enynols and its application to regio- and stereoselective synthesis of fully substituted dihydrofurans.

Efficient synthetic approaches to stereodefined (Z)-enynols have been developed through zirconium-mediated cross-coupling reactions of three different components involving alkyne, ketone, and alkynyl bromide in a one-pot procedure. The subsequent electrophilic cyclization of a wide variety of (Z)-enynols affords fully substituted (Z)-5-(1-iodoylidene)-2,5-dihydrofurans with high regio- and stereoselectivity under mild reaction conditions.

Furans↗