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PubMed1990

Cyclic fatigue-crack propagation, stress-corrosion, and fracture-toughness behavior in pyrolytic carbon-coated graphite for prosthetic heart valve applications.

Fracture-mechanics tests were performed to characterize the cyclic fatigue, stress-corrosion cracking, and fracture-toughness behavior of a pyrolytic carbon-coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing "atomically" sharp precracks, both in room-temperature air and principally in a simulated physiological environment of 37 degrees C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistance-curve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa square root of m, and subcritical stress-corrosion crack velocities (da/dt) which were a function of the stress intensity K raised to the 74th power (over the range approximately 10(-9) to over 10(-5) m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue-crack growth rates (da/dN) were seen to be a function of the 19th power of the stress-intensity range delta K (over the range approximately 10(-11) to over 10(-8) m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress-intensity levels, cyclic fatigue in pyrolytic carbon-coated graphite is reasoned to be a vital consideration in the design and life-prediction procedures of prosthetic devices manufactured from this material.

Biocompatible Materials↗

PubMed1992

Domain walls on graphite mimic DNA.

We show that domain walls on graphite are very likely to mimic features of extended macromolecules like DNA strands, when imaged with an STM. We explain with a simple model how different translational periods along a grain boundary originate from different relative orientations of the graphite lattice at the domain wall. We show how simple geometrical analysis of the images can be used to distinguish true macromolecular features from artifacts.

Artifacts↗

PubMed1990

Separation of anionic and cationic compounds of biomedical interest by high-performance liquid chromatography on porous graphitic carbon.

The separation of small, ionizable compounds of biomedical interest on porous graphitic carbon is described. The retention of anionic compounds is dominated by electronic interaction between the solute and the delocalized electron clouds on the graphitized carbon, while cationic compounds are mainly retained by reversed-phase interaction with the hydrophobic carbon surface. Anionic and cationic compounds can be separated simultaneously with a mobile phase containing an electronic modifier (e.g., trifluoroacetic acid) and an organic modifier (e.g., acetonitrile) for elution. Examples of applications include the measurement of oxalic acid in urine, the determination of creatine and creatinine in urine and in serum, the separation of basic drugs (remoxipride and FLA 981) and the simultaneous analysis of pertechnetate anion and the cationic technetium-amine complexes.

Anions↗

PubMed1990

[Etiology of lung cancer in workers of graphite industry].

Carcinogenic hazards for workers of certain plants of steel, asbestos, oil-producing, oil-refining and chemical industries were studied. Potential carcinogenic hazards for workers of graphite industry conditioned mainly by coke and graphite dust adsorbed polycyclic hydrocarbons, particularly, benzo(a)pyrene made the case for cancer epidemiologic studies which were carried out at some of those plants in the 70s. Exposure to polycyclic hydrocarbons adsorbed on industrial dust was shown to significantly increase the incidence of lung cancer.

Benzopyrenes↗

PubMed1989

Graphite pneumoconiosis and its declining prevalence in Sri Lanka.

A study of underground miners in a graphite mine in Sri Lanka was conducted in 1987. Twelve (3.4%) of the 340 workers examined had radiographic lesions suggestive of graphite pneumoconiosis. In comparison, a survey carried out in another mine in Sri Lanka in 1972 showed that 63 (18.3%) of the 344 workers examined had similar lesions. Though the two surveys were comparable, they were conducted in two different mines. Therefore, the conclusion that the reduction in the prevalence of graphic pneumoconiosis was due to the introduction of improved dust control measures could only be tentative.

Adult↗

PubMedDate not supplied

Graphite foreign body of the conjunctiva simulating melanoma.

A case of a growing vascular pigmented mass of the conjunctiva resembling a melanoma in a patient with a history of a pencil injury to the eye is presented. The lesion was surgically removed and histopathologically found to be a graphite foreign body granuloma. In the differential diagnosis of enlarging pigmented conjunctival lesions, graphite foreign body granuloma should be considered.

Adult↗

PubMed1978

Determination of aluminum in biological samples by atomic absorption spectrophotometry with a graphite furnace.

Aluminum, generally considered non-essential and non-toxic, may accumulate in toxic amounts in the brain in cases of chronic renal failure. We describe a procedure for its analysis in biological fluids by atomic absorption spectrophotometry with a graphite furnace. No sample preparation is required and the procedure is sensitive at the appropriate concentrations. A sample of serum or urine is pipetted into the interior of the graphite tube, where it is sequentially dried, charred, and atomized. Precautions for sample handling are discussed and instrument settings are defined. Precision and accuracy of the method are evaluated, as are the effects of salts, protein content of serum, and specific gravity of urine. Serum of 23 persons who were not consuming aluminum-containing antacids contained 28 +/- 9 (SD) microgram of Al per liter (1.02 +/- 0.33 mumol/liter).

Aluminum↗

PubMed1989

Electronic interaction chromatography on porous graphitic carbon. Separation of [99mTc]pertechnetate and perrhenate anions.

The oxo anions of technetium-99m and rhenium, pertechnetate (TcO4-) and perrhenate (ReO4-), have been separated by high performance liquid chromatography on porous graphitic carbon with aqueous trifluoroacetic acid or salt solutions as eluent. Chromatographic retention was a result of electronic interaction between the lone pair electrons of the anions and the delocalised pi-electron clouds of the porous graphitic carbon. Retention and resolution can be controlled by the concentration and/or species of eluents which can compete with the solutes for electronic interaction being used for elution.

Anions↗

PubMedDate not supplied

Determination of organosilicon oxide polymers in tissue by atomic absorption spectroscopy using HGA graphite furnace.

A simple method of extraction and determination of organosilicon oxide polymers (silicones) in 0.1-0.5 g of formalin fixed tissue by atomic absorption spectroscopy is described. Before the tissue is extracted with n-heptane, it is dried in a desiccator containing concentrated sulphuric acid. The graphite tubes in the HGA graphite furnace are tubes with L'vov platform. The evaporation of n-heptane and a part of the charing of the tissue extract in the tube are done in the presence of oxygen (air). The significance of the employment of L'vov platform and the presence of oxygen are discussed. The methods detection limit (2 X S.D.) is about 0.009 microgram silicon/ml tissue extract which corresponds to about 0.5 microgram polydimethylsiloxane/g tissue.

Dimethylpolysiloxanes↗

PubMed1986

Determination of silver in biological samples using graphite furnace atomic absorption spectrometry based on Zeeman effect background correction and matrix modification.

A method for the determination of silver in human body fluids and biological material is described. The silver in an acid digest of biological samples and diluted body fluids is quantified using Zeeman graphite furnace atomic absorption spectrometry (ZGFAAS). The effects of NH4H2PO4 as matrix modifier and standard addition are discussed. Atomization from the graphite tube wall and from the pyrolytical tube with platform is also discussed and the peak height and the peak area are compared. The best results were achieved by using matrix modification, stabilized temperature platform furnace, integrated absorbance and standard addition technique. The calibration was linear up to 15 micrograms X L-1; the between-run precision was 5.9% at 40 micrograms X kg-1 of silver.

Animals↗

PubMed1991

Determination of gadolinium in biological materials using graphite furnace atomic absorption spectrometry with a tantalum boat after solvent extraction.

A method was developed for the determination of gadolinium (Gd) in biological material using graphite furnace atomic absorption spectrometry (GFAAS). The element is first extracted into methyl isobutyl ketone and then reextracted into hydrochloric acid. Factors influencing the recovery of extraction such as pH, choice of chelating agents, and hydrochloric acid concentration have been investigated. The element is determined under STPF (stabilized temperature platform furnace) conditions with atomization from a tantalum boat. Under optimized furnace conditions, the use of the tantalum boat improved sensitivity substantially compared to the use of pyrolytically coated graphite tubes. Around 150 measurements could be performed with 1 boat. Memory effects, being a common problem in the GFAAS determination of lanthanoids, were no longer observed after insertion of the boat. The characteristic mass and detection limit (2SD; SD = standard deviation) of the Gd determination are 1000 and 2060 pg, respectively. The precision evaluated as the relative standard deviation (RSD) of six analyses was below 10% for tissue Gd concentrations ranging from 0.92 to 72.0 micrograms g-1. The recovery of added analyte ranged between 92.0% and 99.3%. The method was found to be suitable for studying the pharmacokinetics and biodistribution of Gd in rats.

Animals↗

PubMed1990

Determination of subnanogram per cubic meter concentrations of metals in the air of a trace metal clean room by impaction graphite furnace atomic absorption and laser excited atomic fluorescence spectrometry.

Air, drawn by vacuum through a jet, was impacted against the inside surface of an atomic absorption graphite electrothermal atomizer (ETA). The amounts of the particles thus collected were determined at the ng m-3 level by graphite furnace atomic absorption or at the pg m-3 level by laser excited atomic fluorescence. The overall reproducibility of two sets of measurements, made 7 months apart, was 23%, with no significant difference between the two sets of data, based on Student's "t" test at the 95% confidence level. Short-term reproducibility varied from 13% to 34% depending upon the air concentration of the metal. The method shows promise for monitoring long-term effectiveness of the filtering systems in trace metal clean rooms. It was not possible to test for accuracy, due to the low concentrations involved, but accuracy was expected to be within a factor of 2 or 3 of the actual value, based on theoretical aspects of impaction.

Air↗

PubMed1992

Direct determination of zinc in serum by Zeeman atomic absorption spectrometry with a graphite furnace.

We developed a precise and accurate graphite furnace atomic absorption spectrometric method for the direct determination of zinc in serum. Serum samples are analyzed after 20-fold dilution with water of ultrapure analytical grade. No other reagent is used, from the moment of sampling until measurement. During atomization, the argon flow is kept at 150 mL/min instead of gas stop, to decrease the sensitivity and thus allow lower dilution ratios. Zinc concentrations are determined against a serum-matched calibration curve. Graphite tubes are uncoated and no L'vov platform is used. Between-run CVs were 5.9%, 3.5%, and 1.9% for serum zinc concentrations of 0.93, 1.15, and 1.43 mg/L, respectively. The characteristic mass was 9 pg, and the detection limit (meanblank + 3SDblank) was 0.060 mg/L.

Adult↗

PubMed1978

Evaluation of polytetrafluoroethylene-graphite-coated total hip prostheses in goats.

This study was designed to determine if a porous polytetrafluoroethylene-graphite coating could furnish long-term stabilization of total hip prostheses. Prostheses were surgically implanted in 12 mature goats, which were observed postoperatively for as long as 1 year. Effective stabilization occurred in only 4 animals. Poor results in the other animals were attributed to lack of stabilization of the prostheses following initial implantation, which allowed movement at the interface between bone and polytetrafluoroethylene-graphite.

Animals↗

PubMed1975

Two-year biocompatibility study of ORNL graphite.

A new grade of graphite-isotropic, fine-grained, and of superior strength-has been produced at the Oak Ridge National Laboratory. The possibility of using this material in orthopedic implants is under study at the University of Illinois. As part of this program, plugs 1/8 in. in diam were inserted in holes drilled in the proximal femur of 2 groups of 8-week old male rabbits. The groups were sacrificed at the end of 1 and 2 years. A single i.m. injection of achromycin was given 2 days prior to sacrifice. Thin sections of the plugs and surrounding tissue were examined by microradiography and optical microscopy (white light, polarizing, and fluorescent). All bone was normal. Minimal evidence of irritation or fibrous encapsulation appeared.

Animals↗

PubMed1978

[Biomechanical efficiency and biocompatibility of lubricating sprays PTFE or graphite (author's transl)].

The screws and plates used in operative treatment of fractures cause moments of friction between the bone screw head and the bone plate hole during the tightening of the screws. This results in hidden damage to the grinding metal surfaces, with the danger of erosion corrosion and in a reduction in the screw force. By covering the screw heads with the lubricating sprays PTFE or graphite friction was significantly reduced, the screw force increased by 40% and extensive damage to the surfaces avoided. Lubricating sprays or their extracts, in fetal calf serum or in dimethylsulfoxide, were added to fibroblast cultures. Toxicity was manifest as changes in the synthesis of DNA, as measured by autoradiography. Sprays or spray extracts in fetal calf serum did not inhibit cell proliferation. In vivo experiments in rats reflected the in vitro results, there being no evidence that toxic substances were released from the sprays by physiological solvents: There was a lack of histopathological changes in the inner organs and a local encapsulation of implants which was essentially like that in a teflon control group.

Aerosols↗

PubMed1992

Amperometric enzyme sensor for glucose based on graphite paste-modified electrodes.

Amperometric enzyme electrode for glucose is described based on the incorporation of glucose oxidase (GOD) into graphite paste modified with tetracyanoquinodimethane (TCNQ). The incorporated enzyme exhibits high activity and long-term stability over the earlier TCNQ-based glucose sensor (1). The sensor provides a linear response to glucose over a wide concentration range. The response time of the sensor is 15-50 sec, and the detection limit is 0.5 mM. Stable response to the substrate was obtained during a period of 35 d. Application of the sensor in the plasma analysis is reported.

Biosensing Techniques↗

PubMed1986

Specific tritium labeling of glucosyl- and galactosylceramides at the 6-position of the carbohydrate moiety using CrO3-graphite.

A new procedure for introducing tritium into the carbohydrate portions of glucosyl- and galactosylceramides was developed using a new catalyst, CrO3-graphite, which specifically oxidizes the primary alcohol group to the aldehyde. About 10% of the glycolipid was converted to the aldehyde and the aldehyde produced was then reduced back to the original form with KB3H4. After methanolysis, more than 96.7% of the radioactivities of [3H]glucosyl- and [3H]galactosylceramides were found to be located in the carbohydrate portions, and the specific activities of the [3H]galactosyl- and [3H]glucosylceramides were 2.08 to 4.30 X 10(4) cpm/nmol, which could be increased greatly by purifying the aldehydes and reducing them with KB3H4. In addition, beta-galactosidase activity was successfully determined with [3H]galactosylceramide as the enzyme substrate; the Km was 18.73 mM and the Vmax was 11.63 nmol/mg/h, indicating that no significant structural modification occurs during the oxidation.

Animals↗