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PubMed1985

Capillary gas chromatographic analysis of volatile and non-volatile organic acids from biological samples as the t-butyldimethylsilyl derivatives.

A quantitative procedure for the analysis of volatile organic acids and lactic acid in silage is described. The samples were extracted with diethyl ether, derivatized by t-butyldimethylsilylation, and then separated by capillary gas chromatography. The same procedure was useful for the identification by gas chromatography/mass spectrometry of organic acids in samples such as the metabolic fermentation products of anaerobic bacteria.

Acids↗
PubMed2003

Reverse Monte Carlo analysis of extended energy-loss fine structure for disordered structures of tetrahedrally coordinated materials: its applicability.

Capabilities of the reverse Monte Carlo method for characterizing the short-range structural correlations of solids were examined in the analysis of extended energy-loss fine structure (EXELFS). Since this method gives a three-dimensional atomic configuration consistent with the experimental EXELFS spectra, one can extract the statistical distributions of bond lengths, coordination numbers and bond angles of atom species of interest, which have been hard to achieve by conventional EXELFS analysis. The method was applied for the determination of amorphous Si structures and the damaged structure of an electron-irradiated SiC crystal. Advantages and disadvantages of the present method over the precise diffraction intensity measurement are discussed.

Carbon↗
PubMed2004

Microstructural analysis of the deformation range under nano-indentation in beta-SiC.

As a powerful tool to analyse microstructural evolution under irradiation and the interaction of moving dislocations with radiation-induced defects, a focused ion beam (FIB) method was applied to ion-irradiated SiC followed by the nano-indentation test. An FIB method has excellent capability to prepare thin foils from the area of interest with a high accuracy of location and wide flexibility in the sampling direction. These advantages are demonstrated in the application to Si ion-irradiated SiC by transmission electron microscope observation.

Microscopy, Electron, Transmission↗
PubMed2004

Practical considerations on the determination of the accuracy of the lattice parameters measurements from digital recorded diffractograms.

The influence of magnification and defocus on the precision Delta d/d of lattice parameter measurements have been studied by evaluating the diffraction vector length and the signal-to-noise ratio (SNR) of the diffraction peaks in diffractograms calculated by fast Fourier transformation (FFT) of digitally recorded images. Examples are perfect crystals (Si and SiC) and defective crystals (two- and three-dimensional defects within SiC). It is shown that the precision is independent of the diffuseness of the FFT reflections caused by defocus changes or by two-dimensional defects. For the case of a perfect and/or a defective but unstrained crystal, the precision Delta d/d is linearly dependent on the diffraction vector length. For optimal conditions, the highest precision is 0.002. For a defective crystal containing precipitates (nanocrystals), it was found for both the matrix and the nanocrystals that the precision of the measurement is determined by the contribution of strain value (Delta d/d)(strain) of the defective crystal and accuracy Delta d/d for the perfect matrix crystal.

Crystallography↗
PubMed1988

Studies on the t-butyldimethylsilyl group as 2'-O-protection in oligoribonucleotide synthesis via the H-phosphonate approach.

Two model compounds, 1 and 2, have been studied to test the stability of the t-butyldimethylsilyl (t-BDMSi) group towards conditions used during chemical synthesis of RNA fragments by the H-phosphonate approach. When 1 was treated with anhydrous acid for 16 h both the H-phosphonate diester and the t-BDMSi group remained intact. Removal of the t-BDMSi group from 2 with 1.0 M tetrabutylammonium fluoride (TBAF .3H2O) in THF was complete within 4 h and neither concomitant cleavage nor migration of the phosphodiester linkage could be detected even after 24 h. The dimer 2 was not completely stable towards concentrated aqueous ammonia and both loss of the t-BDMSi group and concomitant cleavage of the phosphodiester linkage occurred upon prolonged treatment. These reactions were substantialy suppressed in ethanol containing ammonia solutions, however to alleviate this problem during oligoribonucleotide synthesis, more labile protecting groups for heterocyclic bases would be desired. In conclusion, these studies indicate that 2'-O-t-BDMSi can be considered as a convenient and safe protecting group, which should secure synthesis of oligoribonucleotides with exclusively 3'-5' internucleotidic linkages.

Ammonia↗
PubMed1990

Enzymatic and NMR analysis of oligoribonucleotides synthesized with 2'-tert-butyldimethylsilyl protected cyanoethylphosphoramidite monomers.

The regioisomeric integrity of the internucleotide phosphate linkage in synthetic RNA using 2'-tert-butyldimethylsilyl protection was examined using enzymatic and NMR techniques. Two sets of DNA-RNA hybrid nonamers, T3XT5 and T5XT3 (where X = rA, rC, rG and U) and the tetramer AGCU were analyzed. Enzyme catalyzed hydrolysis of the nonamers with ribonuclease T2 showed that the linkage at the ribonucleotide was the desired 3'-5'. A control nonamer with a 2'-5' linkage was subjected to the enzyme, and showed no cleavage. High-resolution proton NMR of the tetramer also gave a favorable comparison with the same molecule obtained by non-chemical means.

Base Sequence↗
PubMed1992

The viability of revascularized calvarial bone graft in a pig model.

This study compared the vascularity and resorption of calvarial bone flaps based on an undisturbed pedicle and on a previously (4 weeks) detached pedicle of the superficial fascia (galea) and periosteum and free calvarial bone grafts. Nine adult pigs were used, in three of which a silicone rubber compound was injected intravascularly immediately after the transfer confirmed the vascularity of both pedicled bone flaps. In six pigs, volume changes were assessed intraoperatively by a water displacement method and also 12 weeks postoperatively. Both pedicled bone flaps preserved their original volume, whereas free skull grafts showed approximately 50% of volume loss (p less than 0.001). Decalcified hematoxylin and eosin sections of the specimens obtained 12 weeks postoperatively showed a normal calvarial appearance in both pedicled bone flaps and extensive fibrous tissue infiltration into free grafts. It is suggested that a previous detachment of galea and periosteum does not interfere with the use of vascularized calvarial bone graft, which may provide a more predictable result than a free bone graft.

Animals↗
PubMed1994

Silicon tissue assays in nonaugmented cadaveric patients: is there a baseline level?

Microscopic silicone in various tissues in the bodies of females with breast implants has led to the possible incrimination of these implants with connective-tissue disorders. Current technology precludes accurate silicone measurements, but all compounds containing the element silicon (which would include silicone) may be measured accurately. Direct positive correlations of silicon assays with silicone measured levels were confirmed by adding known amounts of silicone oil as a control. With the ubiquitous nature of organosilicons (food containers, syringes, etc.), we hypothesized that baseline silicon levels could be detected in tissues of cadavers without silicone breast augmentation. Ten cadavers were examined. Tissue samples were derived from subcutaneous fat, nipple, breast tissue, liver, spleen, and axillary nodes. Nine of 10 cadavers had silicon levels in various tissues. Measurements were performed by direct current atomic emission spectroscopy. The baseline data were compared with those from four augmented patients who underwent capsulectomies and implant removal. Silicon levels were fivefold higher in the augmented patients than in the nonaugmented cadavers. No difference in levels was noted if the patient had an intact or ruptured implant and/or was symptomatic versus asymptomatic for immunologic disease. This study was designed to measure baseline silicon levels in the normal population. It also has established an accurate level of measurement of tissue silicone.

Aged↗
PubMed1997

Vascular and neural anatomy of the thenar area of the hand: its surgical applications.

Thirty fresh cadaver hands were injected with a silicone rubber compound (Microfil) and dissected to examine the vascular and neural supplies of the thenar area. In 10 specimens, a selective injection technique was used to determine the extent of skin territory nourished by the superficial palmar branch of the radial artery. The purpose of this study was to clarify the anatomic basis for clinical applications of vascularized free- or island-flap transfers from the thenar area. The superficial palmar branch of the radial artery was found in all hands; the average diameter of the branch measured at its bifurcation site was 1.4 mm (0.8 to 3.0 mm). The constant area nourished by the superficial palmar branch was an area approximately 4 x 3 cm located over the proximal parts of the abductor pollicis brevis and opponens pollicis muscles. These results indicate that a fasciocutaneous flap from the radial thenar region can be raised based on the superficial palmar branch and consistently transferred as a free flap. In 63 percent of the hands dissected, the superficial palmar branch was connected to other arteries in the palm, suggesting that the flap can be transferred as a reverse-pedicle island flap in such hands. Innervation of the flap was provided chiefly by a branch of the superficial radial nerve. The radial aspect of the thenar eminence can provide a new and useful donor source for an innervated and vascularized free- or island-flap transfer for reconstruction of various skin defects of the volar side of the fingers.

Arteries↗
PubMed2001

Acute biomechanical and histological effects of intradiscal electrothermal therapy on human lumbar discs.

STUDY DESIGN: Human cadaver lumbar spines were used to assess the acute effects of intradiscal electrothermal therapy in vitro. OBJECTIVE: To determine whether intradiscal electrothermal therapy produces acute changes in disc histology and motion segment stability. SUMMARY OF BACKGROUND DATA: Intradiscal electrothermal therapy has been introduced as an alternative for the treatment of discogenic low back pain. Several hypothesized mechanisms for the effect of intradiscal electrothermal therapy have been suggested including shrinkage of the nucleus or sealing of the anulus fibrosus by contraction of collagen fibers, and thermal ablation of sensitive nerve fibers in the outer anulus. METHODS: Intradiscal electrothermal therapy was performed with the Spinecath by Oratec on 19 fresh, frozen human lumbar cadaver specimens. In a separate study, eight specimens were tested biomechanically and instrumented to map the thermal distribution, whereas five specimens were tested only biomechanically, both before and after intradiscal electrothermal therapy. Six additional specimens were heated with intradiscal electrothermal therapy, and the resulting canal was backfilled with a silicone rubber compound to allow colocalization of the catheter and anular architecture. RESULTS: A consistent pattern of increased motion and decreased stiffness was observed. For the specimens in which only biomechanical measurements were taken, a 10% increase in the motion, on the average, at 5 Nm torque was observed after intradiscal electrothermal therapy. No apparent alteration of the anular architecture was observed around the catheter site in the intradiscal electrothermal therapy-treated discs. CONCLUSION: The data from this study suggest that the temperatures developed during intradiscal electrothermal therapy are insufficient to alter collagen architecture or stiffen the treated motion segment acutely.

Adult↗
PubMed1989

The UW solution for canine kidney preservation. Its specific effect on renal hemodynamics and microvasculature.

The preservation effects of UW solution on renal hemodynamics and microvascular systems were studied in canine kidney autografts. In 72-hr UW-preserved kidneys, the microvessels of both cortex and medulla were completely visualized with silicon rubber compound 1 hr after reperfusion. Histology also showed extremely well-preserved arterioglomerular and tubular systems. These results were correlated with good renal blood flow, prompt recovery of posttransplant graft function, and 100% two-week survival of dogs. In contrast, kidneys preserved for 72 hr with Euro-Collins solution showed necrotic and obstructive changes of the microvasculature and deterioration of renal hemodynamics. In 120-hr UW-preserved kidneys, the microcirculation of the medullary region became poor after reflow when there was fairly intact perfusion of the cortical region, indicating an ischemia-related intrarenal blood flow maldistribution. The 120-hr kidneys subsequently failed in spite of having a good blood flow and morphologically well-maintained microvasculature after reperfusion. These data demonstrated that much, but not all, of the beneficial effect of UW solution in kidney preservation might be attributed to its remarkable protection of renal microvasculature. Correction of intrarenal blood maldistribution caused by a discrepancy in tolerance to ischemia of the vascular and tubular systems might be important in successfully preserving the kidney for 120 hr.

Adenosine↗
PubMed2000

Three-dimensional finite element analyses of four designs of a high-strength silicon nitride implant.

The effects of implant shape and size on the stress distribution around high-strength silicon nitride implants under vertical and oblique forces were determined using a three-dimensional finite element analysis. Finite element models were designed using as a basis the serial sections of the mandible. Using Auto-CAD software, the model simulated the placement of implants in the molar region of the left mandible. Results of the analyses demonstrated that mainly the implant root shape and the directions of bite forces influence the stress distributions in the supporting bone around each implant. Implant size is a lesser factor. The serrated implants presented a larger surface area to the bone than either the cylindrical or tapered implants, which resulted in lower compressive stress around the serrated implants. With increasing implant diameter and length, compressive stress decreased. The mean compressive stress distribution on the serrated implants was more flat (platykurtic) than on either the cylindrical or tapered implants. Results of studies on two load directions (vertical and oblique) showed that, in either case, the compressive stress in the cortical bone around the neck of the implant was higher than in the cancellous bone along the length of the implant. The most extreme principal compressive stress was found with oblique force. This study provides the first information on the relationship between shape of the silicon nitride implant and stress on the supporting bone.

Alveolar Process↗
PubMedDate not supplied

Differentiated growth of human renal tubule cells on thin-film and nanostructured materials.

Over 300,000 Americans are dependent on hemodialysis as treatment for renal failure, and kidney transplantation is limited by scarcity of donor organs. This shortage has prompted research into tissue engineering of renal replacement therapy. Existing bioartificial kidneys are large and their use labor intensive, but they have shown improved survival compared to conventional therapy in preclinical studies and an US Food and Drug Administration-approved phase 2 clinical trial. This hybrid technology will require miniaturization of hemofilters, cell culture substrates, sensors, and integration of control electronics. Using the same harvesting and isolation techniques used in preparing bioartificial kidneys for clinical use, we characterized human renal tubule cell growth on a variety of silicon and related thin-film material substrates commonly used in the construction of microelectromechanical systems (MEMS), as well as novel silicon nanopore membranes (SNMs). Human cortical tubular epithelial cells (HCTC) were seeded onto samples of single-crystal silicon, polycrystalline silicon, silicon dioxide, silicon nitride, SU-8 photoresist, SNMs, and polyester tissue culture inserts, and grown to confluence. The cells formed confluent monolayers with tight junctions and central cilia. Transepithelial resistances were similar between SNMs and polyester membranes. The differentiated growth of human tubular epithelial cells on MEMS materials strongly suggests that miniaturization of the existing bioartificial kidney will be feasible, paving the way for widespread application of this novel technology.

Biocompatible Materials↗
PubMed2004

Relations between macroscopic and microscopic adhesion of Streptococcus mitis strains to surfaces.

Application of physico-chemical models to describe bacterial adhesion to surfaces has hitherto only been partly successful due to the structural and chemical heterogeneities of bacterial surfaces, which remain largely unaccounted for in macroscopic physico-chemical characterizations of the cell surfaces. In this study, the authors attempted to correlate microscopic adhesion of a collection of nine Streptococcus mitis strains to the negatively charged, hydrophilic silicon nitride tip of an atomic force microscope (AFM) with macroscopic adhesion of the strains to a negatively charged, hydrophilic glass in a parallel-plate flow chamber. The repulsive force probed by AFM upon approach of the tip to a bacterial cell surface ranged from 1.7 to 7.7 nN depending on the strain considered and was found to correspond to an activation barrier, governing initial, macroscopic adhesion of the organisms to the glass surface. Moreover, maximum distances at which attractive forces were probed by the AFM upon retraction of the tip (120 to 1186 nm) were related to the area blocked by an adhering bacterium, i.e. the distance kept between adhering bacteria. Bacterial desorption could not be related to adhesive forces as probed by the AFM, possibly due to the distinct nature of the desorption process occurring in the parallel-plate flow chamber and the forced detachment in AFM.

Bacterial Adhesion↗