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At least 793 records · Page 44Linked to original sources
PubMed1996

Evaluating sol-gel ceramic thin films for metal implant applications. I. Processing and structure of zirconia films on Ti-6AI-4V.

Thin ceramic films or coatings over metallic bone-interfacing implant surfaces have the potential to improve implant performance with respect to implant fixation, wear, or corrosion. In this study, zirconia (ZrO2) thin films formed on Ti-6AI-4V using a polymeric alkoxide-based solgel process were investigated. ZrO2 films of uniform thickness on the order of 100 nm were obtained by dip coating Ti-6AI-4V samples into a zirconium propoxide containing solution using a substrate withdrawal speed ranging from 2 to 8 cm/min and a sol of nominal viscosity approximately 6 cps. These films were essentially free of surface macrodefects but had random submicron "pinholes." X-ray diffraction studies suggested that the films were at least partially crystalline, with some "metastable" cubic and/or tetragonal phases after annealing for 1 h at 500 degrees C. The demonstrated reproducibility of this approach for producing good quality ZrO2 films on Ti-6AI-4V warrants further studies to optimize processing conditions for implant applications.

Alloys↗
PubMed2005

Metal phosphonates applied to biotechnologies: a novel approach to oligonucleotide microarrays.

A new process for preparing oligonucleotide arrays is described that uses surface grafting chemistry which is fundamentally different from the electrostatic adsorption and organic covalent binding methods normally employed. Solid supports are modified with a mixed organic/inorganic zirconium phosphonate monolayer film providing a stable, well-defined interface. Oligonucleotide probes terminated with phosphate are spotted directly on to the zirconated surface forming a covalent linkage. Specific binding of terminal phosphate groups with minimal binding of the internal phosphate diesters has been demonstrated. The mixed organic/inorganic thin films have also been extended for use arraying DNA duplex probes, and therefore represent a viable general approach to DNA-based bioarrays. Ideas for interfacing mixed organic/inorganic interfaces to other bioapplications are also discussed.

Binding Sites↗
PubMed1979

[Analytical methods for nitrate and nitrite determination in foods. 3. Spectrophotometric determination of nitrate and nitrite using sulphanilic acid/1-naphylamine, and of nitrite using resorcinol/zirconium (IV) oxychloride].

The Nitrate content of foods may be determined by means of azo-dye coupling after reduction of the nitrate with the aid of active cadmium produced in the sample solution. An easy method for determining nitrite consists in the colorimetric estimation of a coloured chelate formed from nitrite, resorcinol and zirconium(IV) oxychloride.

1-Naphthylamine↗
PubMed1994

Evaluation of carcinogenicity and chronic toxicity associated with orthopedic implants in mice.

The carcinogenicity and chronic toxicity of 316L stainless steel, nickel, Ti-6A1-4V, hydroxyapatite (HA)-coated Ti-6A1-4V, aluminum oxide containing yttrium oxide, and zirconium oxide containing yttrium oxide were evaluated by implanting solid rods of each material in the thigh muscle of C57BL/6N mice for 24 months. Nickel alloy showed high carcinogenic and toxic potencies, whereas other materials showed no evidence of them. Tumors retaining nickel alloys were malignant fibrous histiocytoma or fibrosarcoma. In some cases, lymphomata that seemed to develop spontaneously were found around the implants because lymphocytes were known to accumulate in chronic inflammatory lesions, and this phenomenon also might be applied to lymphoma.

Alloys↗
PubMed2006

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.

Alloys↗
PubMed2006

Solvent and temperature gradients in separation of synthetic oxyethylene-oxypropylene block (co)polymers using high-temperature liquid chromatography.

Chromatographic behavior of synthetic block (co)oligomer samples (EO)n(PO)m(EO)n and (PO)n(EO)m(PO)n with different distribution of propylene oxide (PO) and ethylene oxide (EO) monomer units was investigated on three types of stationary phases on zirconium dioxide support: Zr-PS (polystyrene), Zr-carbon, and Zr-carbon C18. The effects of the distribution and sequence of the oxyethylene and oxypropylene monomer units on the chromatographic retention depend on the type of the stationary phase, but are strongly affected by the organic modifier (methanol or ACN) in aqueous-organic mobile phase. Special attention was focused on the influence of the mobile-phase composition on the separation according to the EO and PO distribution. Zirconia-based columns are stable at elevated temperatures and can be used in high-temperature LC (HTLC); hence, we investigated the temperature effects on the chromatographic behavior up to 90 degrees C. The applications of solvent and temperature gradients were compared on the zirconia stationary phases in the RP mode.

Carbon↗
PubMed1991

Laser trabecular ablation (LTA).

As part of a pilot study for glaucoma surgery, the use of 3 infrared solid state lasers with 4 fiber optic delivery systems to ablate human trabecular meshwork was investigated. Laser trabecular ablation (LTA) was attempted with the Erbium:YAG (2.94 microns), Erbium:YSGG (2.79 microns), and Holmium:YSGG (2.1 microns) lasers. Laser energy was delivered as a single pulse (250 microseconds) by tissue fiber optic contact with low hydroxyl-fused silica (200 and 500 microns), zirconium fluoride (250 microns), or sapphire (250 microns) fiber optics. Total energy required and thermal effects decreased as laser wavelength increased. LTA was best achieved at 2.94 microns (4 mJ total energy; energy densities = 8.2-12.7 J/cm2; pulse length 250 microseconds) with average thermal damage zones of 5.3-10.3 +/- 1.3-2.4 microns (means +/- SDs) to contiguous structures. This finding has potential applications in the surgical treatment of open-angle and congenital glaucoma and may minimize failure rates seen in other types of surgery on the trabecular meshwork where disrupted trabecular meshwork is not removed.

Aluminum Oxide↗
PubMed1999

Large-magnitude high-spin nuclear parameters in a Ti3+ center from X-band EPR measurements at 10 K.

Precise 10 K X-band EPR measurements and subsequent spin-Hamiltonian analysis by direct matrix diagonalization methods are reported for a Ti3+ (S = 1/2) center in tetragonal zircon (zirconium silicate, ZrSiO4). A special, and previously unobserved, feature of the supposedly uniaxial spectrum is the marked angular dependence of the titanium hyperfine lines in the perpendicular, ab crystal plane. As discussed, this can only arise from the presence of high-spin nuclear terms of dimension BIk, SIk (k = 3, 5) in the spin Hamiltonian. Parameters arising from these terms were determined to have magnitudes very much larger than observed previously in first-row transition ions. The consequences of precise determination of these high-spin parameters are significant and several: a precise determination of the nuclear quadrupole tensor leading to a ratio 47P/49P in excellent agreement with the ratio derived from the corresponding nuclear quadrupole moments; an apparent anisotropy in the nuclear Zeeman interaction which can be identified with anisotropy in the chemical shielding "tensor"; a marked hyperfine anomaly. The origin and significance of these observations are discussed.

Anisotropy↗
PubMed1981

The monocyte-macrophage system in granulomatous inflammation.

Granulomas may be immunologically induced or non-immunologically induced. In immunologically induced granulomas cells of the monocyte-macrophage series take on the appearance of epitheloid cells. Ultrastructurally epithelioid cells may have a secretory appearance with much rough endoplasmic reticulum or take on highly degenerate vesicular appearance. Other epithelioid cells look like activated macrophages. Secretory epithelioid cells may be found associated with acute local inflammation as in borderline tuberculoid leprosy in reaction, the lepromin reaction, following injection of BCG vaccine and in experimental zirconium granulomas. In these situations there may also be strong histological and biochemical evidence of increased fibroblast activity and collagen synthesis. It is suggested that these cells are actively secreting a fibroblast-activating factor. Epithelioid cells may lose their Fc receptors, undifferentiated macrophages in lepromatous leprosy can lose their C3 receptors. It is suggested that in a number of situations granuloma formation may be associated with complement activation through the alternative pathway as in the case of mycobacterial granulomas. Toxic granulomas produced by metals may be caused by C3 being split by plasmin after conversion from plasminogen by activation of the Hageman factor.

Animals↗
PubMed1993

Chemistry of zirconia and its use in chromatography.

The purpose of this review is to shed some light on the complex properties of zirconia's surface chemistry in order to better understand its behaviour under chromatographic conditions. We emphasize the great differences between the much better known chemistry of a silica surface and the chemistry of zirconia's surface. The review describes both the physical and chemical properties of zirconium dioxide from a chromatographic point of view. The chemistry of monoclinic zirconia surface is developed from its underlying crystalline structure. The paper describes the dependence of the specific surface area, pore volume, porosity and mechanical strength on thermal treatment. Methods of synthesis of chromatographically useful zirconia are outlined. The review also covers the adsorption properties of zirconia at both gas-solid and liquid-solid interfaces. Adsorption of water, carbon dioxide, carbon monoxide and ammonia are described and the controversies concerning the surface concentration of adsorption sites are presented. The complex chemistry of a zirconia surface is pointed out and the importance of ligand exchange reactions is emphasized. In contrast to a silica surface, ligand exchange plays an important role in liquid chromatographic applications of zirconia. Strong, hard Lewis acid sites, present on a zirconia surface, can interact with hard Lewis bases and these interactions, sometimes troublesome, can be successfully exploited even for protein separations. Zirconia's surface can be modified in many ways: dynamically, by addition of competing Lewis bases to the mobile phase, or permanently, by covering its surface with polymers or by depositing carbon. The review also shows that the main difficulty in achieving a wider variety of applications is probably our lack of knowledge and poor understanding of zirconia's surface chemistry.

Chromatography↗
PubMed1993

Studies on radiopaque composites containing ZrO2-SiO2 fillers prepared by the sol-gel process.

Radiopacity can facilitate diagnostic observations adjacent to dental composites. To produce radiopaque SiO2-based fillers, ZrO2-SiO2 powders containing up to 45wt% ZrO2 were manufactured by the sol-gel process. The radiopacity of experimental composites containing Bis-GMA+TEGDMA+CQ+DMAEMA monomer mixture (25 wt%) and ZrO2-SiO2 fillers (75 wt%) was evaluated and compared to that of human enamel and two commercial composites with different radiopacity. It became evident that the radiopacity of the experimental composites increased linearly with zirconium content and could match that of the control materials, while the composite containing 15wt% ZrO2-85wt% SiO2 filler possessed radiopacity analogous to that of human enamel. It was demonstrated here that the radiopacity of the composites could be precisely controlled by adjusting the ZrO2 content in ZrO2-SiO2 fillers. These radiopacity-adjustable composites have the potential to be very useful filling materials by enabling dentists to accurately distinguish secondary caries adjacent to the composite restorations.

Analysis of Variance↗
PubMed1990

Method for ultrastructural studies of the intact tissue-metal interface.

Samples were prepared for ultrastructural studies of the intact interface between metallic implants and tissue by transmission electron microscopy. The method is based on plastic embedding of implant and tissue and subsequent removal of the bulk metal by electrochemical dissolution (electropolishing), to facilitate preparation of ultrathin sections for transmission electron microscopy. Surface sensitive spectroscopy (Auger electron microscopy and X-ray photoemission spectroscopy) and transmission electron microscopy EDX results show that the method produces samples with an intact interface, containing the implant surface oxide and the adjacent tissue. Examples of application of the method on titanium, zirconium and aluminium implants in soft tissue are given.

Aluminum↗
PubMed1996

Wear characteristics of sliding pairs of zirconia (Y-TZP) for hip endoprostheses.

Femoral ball heads made of aluminium 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 with good wear properties are femoral ball heads made of alumina (Al2O3) articulating against polyethylene (PE-UHMW) acetabular cups (since 1974) and zirconia (Y-TZP) heads articulating against polyethylene cups (since 1986). The best tribological combinations are alumina heads articulating against alumina cups. Zirconia has better mechanical properties (for example, bending strength or fracture toughness) than alumina. Therefore R&D is going on to design zirconia acetabular cups. The wear characteristics of zirconia (Y-TZP) articulating against itself were investigated using a ring-on-disc testing device according to ISO 6474. The high wear rate emphasized that medical-grade zirconia (Y-TZP according to ISO/ DIS 13356) should not be used for acetabular cups.

Aluminum↗
PubMed1995

Effects of an antiperspirant with emollients on foot-sweat accumulation and blister formation while walking in the heat.

BACKGROUND: Friction blisters are a common injury in sports activities and military operations. Blisters can compromise performance, so it is important to devise preventive strategies to reduce these injuries. OBJECTIVE: This study investigated the influence of an antiperspirant with emollient additives on frequency and severity of friction blisters, hot spots, and irritant dermatitis. METHODS: Twenty-three healthy men walked on a treadmill (1.39 m/sec, 1% grade) in a warm environment (28 degrees C, 25% relative humidity) carrying a total mass of 21 +/- 1 kg. For 4 consecutive days before the walk, the subjects' feet were treated with either (1) an antiperspirant (20% aluminum zirconium tetrachlorohydrex glycine concentration plus water) with emollient additives, (2) emollient additives alone (placebo control), or (3) nothing (nontreated). In two separate trials (1 month apart) each participant received the antiperspirant treatment and both control treatments (emollient [placebo] and no treatment). RESULTS: No differences were seen among treatment conditions for sweat accumulation (p = 0.86), blister incidence (p = 0.36), hot spot incidence (p = 0.83), or blister severity (p = 0.31). Irritant dermatitis was not reported in any of the treatment conditions. CONCLUSION: The use of an antiperspirant with emollients reduces irritant dermatitis but does not reduce total foot-sweat accumulation, blister or hot spot incidence, or blister severity.

Adult↗
PubMed1993

Evaluation of biocompatibility of various ceramic powders with human fibroblasts in vitro.

Cell reaction to powders of ceramics was studied in vitro. Cultured human fibroblasts were exposed to different types of ceramic powders: zirconia (ZP), alumina (A), tricalcium phosphate (TCP) and hydroxyapatite (HA), at various concentrations. The cell viability at the different exposure times was measured by the colony formation (expressed as colony forming efficiency, CFE), neutral red uptake (NR) and colorimetric tetrazolium (MTT) reduction. Alumina and hydroxyapatite showed no cytotoxic effects at studied doses (1-500 mug/ml) while zirconia and tricalcium phosphate inhibited cell viability, with 50% of CFE reduction at the concentration of about 50 mug/ml. In order to study the cytotoxic mechanism of zirconia powder, two further experiments were included, viz. the cellular response to the sintered zirconia ceramic powders (CZP) which were obtained by crushing the sintered ceramic material; and the measurement of the degradation of zirconia ceramic plate in the different solutions, i.e., either in saline or in 0.02 M lactic acid (pH 2.72). Similar cell reactions were obtained for the CZP and ZP by using MTT and NR assays. Slow releases of ions from zirconia ceramic plate, yttrium in both solutions and zirconium and yttrium in lactic acid, were detected.

Aluminum↗
PubMed1993

In-vitro evaluation of the cytocompatibility of wear particles generated by UHMWPE/zirconia friction.

Cytotoxicity of wear products generated by UHMWPE/yttria partially stabilized zirconia (YPSZ) friction and UHMWPE/surface-nitrided Ti-6Al-4V friction in pseudo-extracellular fluid (PECF) at 37 degrees C was evaluated. Though the amount of abraded UHMWPE against YPSZ was almost the same as that against nitrided Ti-6Al-4V, the wear products generated by UHMWPE/YPZ friction significantly inhibited cell growth while those by UHMWPE/nitrided Ti-6Al-4V friction showed no growth inhibition. Dissolved Zr and Y ions were at least 70 times less than the amount causing growth inhibition. The cytotoxicity was caused mainly by the particles less than 0.22 mum in size. Amorphous zirconium-containing particles (5-20 nm) found in the PECF, formed presumably by stress corrosion, would be a responsible factor for the cytotoxicity.

Biocompatible Materials↗
PubMed1993

Ceramic composites for biomedical applications.

Ceramics have been successfully used for more than twenty years for orthopaedic prostheses, as articulating bearing surfaces against ceramic or polymer components. In both cases, ceramics are characterized by low friction coefficient and low wear rate, compared to metallic materials (stainless steels, titanium and chromium-cobalt alloys). However, their brittleness is much higher than that of metals and presently restricts the use of ceramics for hip joint balls or knee condyles. In the material science field, it is very well known that the association of two different materials can lead to new materials, often called 'composites'. Their properties can be higher than the same properties of each of the individual materials, when taken separately. Nevertheless, the word 'composites' is not universally used with the same meaning. For this reason, we will first give a few definitions in order to clearly understand what can be called 'composite' for ceramic materials. Dispersed phases increase the fracture toughness and high temperature mechanical behaviour of ceramics. In this paper, devoted to medical applications, only mechanical properties at the low (body or room) temperature are analysed. Particular attention is given to the alumina-zirconia system, because aluminium and zirconium oxides are currently accepted as biomaterials for joint prostheses. Finally, a highlight is given on the difficulties in the technological processes to obtain improved ceramic composites.

Aluminum↗
PubMed1975

Comparative percutaneous absorption of pyrithiones.

The percutaneous absorption of 3H or 35S labelled pyridine-2-thione-N-oxide (PT) through the skin of rat, rabbit and guinea pigs in vivo is reported. The sodium (Na) zinc (Zn) and zirconium (Zr) derivatives of PT were studied and the effects of duration of contact and concentration of the NaPT and ZnPT in test solutions were examined. Shampoo test solutions containing the isotopically labelled PT were applied to the skin of the animals. The skins were then rinsed, the treated areas of skin protected and excreta were monitored for the isotope for 2 days after treatment. Penetration was calculated from the amounts of isotope in the excreta. Further groups of animals were treated with test solutions applied under occlusive patches for 6 h before rinsing the skin. The turnover of Na and ZnPT in the three species after intraperitoneal and subcutaneous injection was measured. All three species rapidly excreted the injected isotope principally via the urine. The comparative penetration of the three PT samples was Na greater than Zr greater than Zn from all treatments. The comparative permeability of the animals' skins to these PTs was rabbit greater than rat greater than guinea pig. NaPT penetration was found to be dependent upon duration of contact and concentration in the test solution whereas the penetration of ZnPT was found to be proportional to concentration but independent of duration of contact of the test solution. Extrapolation of these findings to the use of shampoos containing up to 1% (w/v) ZnPT by man indicated an adequate margin of safety for use of this type of product.

Animals↗