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In recent years, titanium has become a material of major interest in prosthetic dentistry. Due to its chemical properties, titanium has to be processed differently from conventional alloys. In this paper, two different methods of welding were investigated. Specimens machined from pure titanium rods were fused either by laser welding or plasma welding. Hardness profiles and light microscopy images were taken in the region of the weld. The mechanical properties were tested by alternating bending fatigue tests up to 3 million cycles. Light microscopy images and hardness profiles showed a larger heat-affected zone after plasma welding compared to laser welding. No significant differences comparing fatigue strength could be found between the two methods of welding. However, extreme loads led to earlier fatigue in the plasma-welded specimens. SEM images of the laser-welded joints showed fractures in the welding zone, while the plasma-welded specimens fractured mostly beyond the heat-affected zone. From these results, it can be assumed that both methods are suitable for welding titanium. At the moment, laser welding is the more suitable technique in dentistry because of its lower thermal alteration of the workpieces.
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PMID:Studies on laser- and plasma-welded titanium. 859 37

The aim of this study was to determine the bond strength of hybrid composite resin to the surface of a gold alloy used in porcelain-fused-to-metal restorations. The surface of the gold alloy was either ground with a sintered diamond burr, sandblasted with Al2O4 or ground with a silicon-carbide stone. The composite resin was bonded to the surface of the gold alloy with or without a commercial silane primer. Bond strength was tested with a three-point loading test, and the elemental composition of the surface of the gold alloy after various mechanical treatments was analysed by SEM/EDS method. Replicas of the fracture surface of the test specimens were examined by SEM to determine whether or not composite resin particles left on the surface had adhered after the loading test. The results showed that mechanical treatment of the surface of the gold alloy affects the bond strength of the composite resin (P < 0.001) but that silane treatment of the surface did not affect the bond strength (P = 0.217). SEM/EDS analysis showed evenly distributed aluminium on the surface of sandblasted gold alloy and silicon on the surface that had been ground with the silicon-carbide stone. This study suggests that sandblasting of the gold alloy surface considerably enhances the strength of its bond to hybrid composite resin.
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PMID:Bonding of hybrid composite resin to the surface of gold-alloy used in porcelain-fused-to-metal restorations. 929 Dec 48

Endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. We explored the effect of a continuous supply of human endothelial NO synthase (eNOS) on the blood pressure of spontaneously hypertensive rats (SHR) by somatic gene delivery. A DNA construct containing the human eNOS gene fused to the cytomegalovirus promoter/enhancer was injected into SHR through the tail vein. A single injection of the naked eNOS plasmid DNA caused a significant reduction of systemic blood pressure for 5 to 6 weeks in SHR, and the effect continued for up to 10 to 12 weeks after a second injection. The differences were significant from 2 to 12 weeks postinjections (n=6, P<.01). In a separate experiment, L-arginine, the substrate of eNOS, was supplied in drinking water at a concentration of 7.5 g/L for 11 weeks after eNOS gene delivery. A maximal blood pressure reduction of 21 mm Hg in SHR was observed with eNOS DNA compared with that of control SHR injected with vector DNA (181.9+/-1.46 versus 202.7+/-2.79 mm Hg, mean+/-SEM, n=6, P<.01). Human eNOS gene delivery induces significant increases in urinary and aortic cGMP levels and urinary and serum nitrite/nitrate content (P<.05), while no significant differences in body weight, heart rate, water intake, food consumption, or urine excretion were observed. These results indicate that somatic delivery of the human eNOS gene induces a prolonged reduction of high blood pressure and raises the potential of using eNOS gene therapy for hypertension and cardiovascular diseases.
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PMID:Prolonged reduction of high blood pressure with human nitric oxide synthase gene delivery. 931 9

Postlarvae of the cestode Hepatoxylon trichiuri (Holten, 1802) were found attached to the surface of viscera of Prionace glauca (Linnaeus, 1758) taken from Atlantic coastal waters off the south coast of Massachusetts, USA. Gross anatomy of the attachment site shows a quadripartite rim surrounding a deep pit with holes corresponding to the penetration site of each tentacle. Hyperplasia of the liver capsule into outgrowths at the attachment site conform to the attachment of the bothridia. The cuboidal epithelium of the liver capsule became columnar forming papillary outgrowths, with a dense fibrotic reaction beneath the attachment site and infiltration by leukocytes and pigment containing granulocytic cells. Blood sinusoids beneath the attachment site are greatly enlarged. Postlarvae attached to the surface of the epigonal organs of three blue sharks were not accompanied by reactions. SEM examination of the scolex of H. trichiuri postlarvae revealed fused pairs of bothridia within infolded muscular lateral rims, porose tegument devoid of microtriches and a bilateral plane of symmetry in the tentacular armature.
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PMID:Histopathological reactions of the blue shark, Prionace glauca, to postlarvae of Hepatoxylon trichiuri (Cestoda: Trypanorhyncha: Hepatoxylidae) in relationship to scolex morphology. 951 95

We previously reported that mutation of the transforming growth factor-beta3 (TGF-beta3) gene caused cleft palate in homozygous null (-/-) mice. TGF-beta3 is normally expressed in the medial edge epithelial (MEE) cells of the palatal shelf. In the present study, we investigated the mechanisms by which TGF-beta3 deletions caused cleft palate in 129 x CF-1 mice. For organ culture, palatal shelves were dissected from embryonic day 13.5 (E13.5) mouse embryos. Palatal shelves were placed singly or in pairs on Millipore filters and cultured in DMEM/F12 medium. Shelves were placed in homologous (+/+ vs +/+, -/- vs -/-, +/- vs +/-) or heterologous (+/+ vs -/-, +/- vs -/-, +/+ vs +/-) paired combinations and examined by macroscopy and histology. Pairs of -/- and -/- shelves failed to fuse over 72 hours of culture whereas pairs of +/+ (wild-type) and +/+ or +/- (heterozygote) and +/-, as well as +/+ and -/- shelves, fused within the first 48 hour period. Histological examination of the fused +/+ and +/+ shelves showed complete disappearance of the midline epithelial seam whereas -/- and +/+ shelves still had some seam remnants. In order to investigate the ability of TGF-beta family members to rescue the fusion between -/- and -/- palatal shelves in vitro, either recombinant human (rh) TGF-beta1, porcine (p) TGF-beta2, rh TGF-beta3, rh activin, or p inhibin was added to the medium in different concentrations at specific times and for various periods during the culture. In untreated organ culture -/- palate pairs completely failed to fuse, treatment with TGF-beta3 induced complete palatal fusion, TGF-beta1 or TGF-beta2 near normal fusion, but activin and inhibin had no effect. We investigated ultrastructural features of the surface of the MEE cells using SEM to compare TGF-beta3-null embryos (E 12. 5-E 16.5) with +/+ and +/- embryos in vivo and in vitro. Up to E13.5 and after E15.5, structures resembling short rods were observed in both +/+ and -/- embryos. Just before fusion, at E14.5, a lot of filopodia-like structures appeared on the surface of the MEE cells in +/+ embryos, however, none were observed in -/- embryos, either in vivo or in vitro. With TEM these filopodia are coated with material resembling proteoglycan. Interestingly, addition of TGF-beta3 to the culture medium which caused fusion between the -/- palatal shelves also induced the appearance of these filopodia on their MEE surfaces. TGF-beta1 and TGF-beta2 also induced filopodia on the -/- MEE but to a lesser extent than TGF-beta3 and additionally induced lamellipodia on their cell surfaces. These results suggest that TGF-beta3 may regulate palatal fusion by inducing filopodia on the outer cell membrane of the palatal medial edge epithelia prior to shelf contact. Exogenous recombinant TGF-beta3 can rescue fusion in -/- palatal shelves by inducing such filopodia, illustrating that the effects of TGF-beta3 are transduced by cell surface receptors which raises interesting potential therapeutic strategies to prevent and treat embryonic cleft palate.
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PMID:Pathogenesis of cleft palate in TGF-beta3 knockout mice. 1043 15

Histidine was baseline separated from histamine, 1-methylhistamine and cis- and trans-urocanic acid using high-performance capillary electrophoresis (HPCE) on a fused-silica column (50 cm x 75 microm) with 0.05 M NaH2PO4 buffer, pH 5.0, and 12 kV. The detection limit of histidine, trans- and cis-urocanic acid was 10(-6) M at a wavelength of 214 nm. The detection limit of the urocanic acid isomers was slightly enhanced to 5 x 10(-7) M at 267 nm. The transformation of the trans-urocanic acid standard in vitro into the cis-isomer was dependent on the time of exposure and the energy of the light source. UVB light induced a significantly faster conversion than UVA light. The HPCE method was used for the characterization and measurement of histidine and urocanic acid in human skin eluates. The concentrations of histidine, trans- or cis-urocanic acid in ethanol washes from the skin of healthy, non-allergic volunteers were 2.22+/-0.40 x 10(-5) 0.96+/-0.26 x 10(-5) and 1.04+/-0.30 x 10(-5) M, respectively, (mean+/-SEM, n=8). The results obtained by HPCE correlated well with data obtained by HPLC. Correlation coefficients of r2=0.981, r2=0.814 and r2=0.956 were found for histidine, trans- and cis-urocanic acid, respectively.
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PMID:Determination of histidine and urocanic acid isomers in the human skin by high-performance capillary electrophoresis. 1112 77

The structure and morphology of a novel form of poly(beta-hydroxybutyrate) produced by gel-spinning is described. The entangled fibrous nature of the material, which resembles 'cotton wool' suggests possible functions in wound scaffolding devices. The surface structure and fibre diameter distribution of the fibres have been investigated using phase contrast and scanning electron microscopy. Fibres were found to possess a variety of surface irregularities, such as pores and indentations. with diameters mainly in the range 1-15 microm. Additionally, individual fibres were occasionally found to be fused or forked together with neighbours. The effects of blending with various polysaccharides and of altering the process solvent on fibre morphology were also investigated. Under hydrolytic degradation conditions (pH 10.6, 70 degrees C) the fibres degraded by gradual fragmentation and erosion to fibre fragments, particulate matter and eventually to monomer. Altering the production process influenced both the fibre diameter distributions and surface morphology of the constituent fibres. Mammalian and human epithelial cells were used to study the cellular interaction with the spun fibres. SEM studies show that there is little or no cell adhesion to the unmodified fibres, but surface treatment by means of acid and alkali washes promoted cell proliferation on the materials, probably as a result of the introduction of hydroxyl and carboxyl at the surface. Fabrication of non-woven mats, which were subsequently acid or alkali treated, provided a conventional way of forming a cell-adhesive matrix which may have potential value as a wound scaffold. Neither cell line exhibited any cytotoxic response to these polymers.
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PMID:Centrifugally-spun polyhydroxybutyrate fibres: effect of process solvent on structure, morphology and cell response. 1148 40

The yield and quality of (a) parthenogenetic blastocysts produced by two activation treatments (cycloheximide [CHX] or 6-dimethylaminopurine [DMAP]) and (b) nuclear transfer blastocysts generated using these two activation treatments and three different ages of karyoplast derived from day 3, 4, or 5 in vitro produced donor embryos, were examined in order to define an optimal nuclear transfer protocol. The two activation protocols comprised calcium ionophore followed by either CHX or DMAP. Parthenogenetic blastocyst yields were greater (P < 0.001) following activation with DMAP than CHX (59.7 +/- 5.1 vs. 31.4 +/- 4.5 [mean +/- SEM]). In contrast, nuclear transfer blastocyst rates per fused embryo were lower (P < 0.0001) using cytoplasts activated with DMAP. The individual rates using day 3, 4, and 5 donors and using CHX and DMAP activation treatments were 31.9 +/- 5.0, 31.7 +/- 6.2, 20.4 +/- 7.3 and 27.8 +/- 4.7, 20.1 +/- 7.5, 12.7 +/- 8.3, respectively. Blastocyst rate per fused embryo was negatively correlated (P = 0.0091) with the total number of blastomeres per donor embryo. Despite this inverse relationship, the calculated potential blastocyst yield per donor embryo was positively correlated (P < 0.0048) to karyoplast age. The individual potential yields on days 3, 4, and 5 and for the two activation protocols (CHX and DMAP) were 4.7 +/- 0.8, 7.2 +/- 1.2, 10.1 +/- 2.1 and 3.8 +/- 0.8, 5.5 +/- 2.1, 7.3 +/- 4.1, respectively. One possible explanation for the observed inverse relationship is that differentiation events during early cleavage are able to reduce the ability of the cytoplast to reprogram the transferred karyoplast and hence reduce blastocyst yields. The mechanism that mediates the differential effect of the CHX and DMAP on blastocysts yields between parthenogenetic and nuclear transfer embryos remains to be elucidated. In conclusion, the results indicate that although activation of oocytes with DMAP can produce a higher percentage of blastocysts, CHX activation is superior for use in nuclear transfer.
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PMID:Effect of two activation treatments and age of blastomere karyoplasts on in vitro development of bovine nuclear transfer embryos. 1159 49

The processes that cause the failure of sheathless electrospray ionization (ESI) emitters, based on different kinds of gold coatings on fused-silica capillaries, are described and explained. The methods chosen for this study include electrochemical methods, ICPMS analysis of the electrolytes used, SEM studies, and electrospray experiments. Generally, the failure occurs by loss of the conductive coating. It is shown that emitters with sputter-coated gold lose their coatings because of mechanical stress caused by the gas evolution accompanying water oxidation or reduction. Emitters with gold coatings on top of adhesion layers of chromium and nickel alloy withstand this mechanical stress and have excellent durability when operating as cathodes. When operating as anodes, the adhesion layer is electrochemically dissolved through the gold film, and the gold film then flakes off. It is shown that the conductive coating behaves as a cathode even in the positive electrospray mode when the magnitude of a superimposed reductive electrophoretic current exceeds that of the oxidative electrospray current. Fairy-dust coatings developed in our laboratory (see Barnidge, D. R.; etal.Anal. Chem. 1999, 71, 4115-4118,) bygluing gold dust onto the emitter, are unaffected by the mechanical stress due to gas evolution. When oxidized, the fairy-dust coatings show an increased surface roughness and decreased conductivities due to the formation of gold oxide. The resistance of this oxide layer is however negligible in comparison with that of the gas phase in ESI. Furthermore, since no flaking and only negligible electrochemical etching of gold was found, practically unlimited emitter lifetimes may be achieved with fairy-dust coatings.
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PMID:Evaluations of the stability of sheathless electrospray ionization mass spectrometry emitters using electrochemical techniques. 1160 37

The purpose of this study was to investigate the enhancement of shortening and of the velocity of shortening during repeated incompletely fused isotonic tetanic contractions. The medial gastrocnemius muscle of anesthetized rats was isolated in situ and the motor nerve stimulated with supramaximal pulses, 50 micros duration, at optimal length. Estimated maximal velocity of shortening (V(max)) was 210 +/- 6 mm x s(-1) (mean +/- SEM). Repeated incompletely fused tetanic contractions (three pulses at 80 Hz) resulted in initial shortening which was 1.5 +/- 0.1 mm, and this increased to 2.7 +/- 0.2 mm after 7 s of 4 s(-1) contractions. Peak velocity of shortening for intermittent 80 Hz stimulation increased from 60.5 +/- 4 mm x s(-1) to 91.8 +/- plus minus 6 mm x s(-1). The initial velocity of shortening for 80 Hz stimulation was substantially less than the velocity of shortening observed with 200 Hz stimulation, but increased to 72 +/- 3% of the load-specific value for 200 Hz stimulation. Myosin regulatory light chain phosphorylation increased from 11.1 +/- 1.5% at rest to 32.9 +/- 5.4% after 4 s of intermittent 80 Hz stimulation and 50.4 +/- 8.8% after 7 s ( P<0.01). The ascending limb of the length-force relationship was determined with tetanic contractions, 200 Hz for 100 ms. At the length corresponding to peak shortening after 7 s of repeated 80 Hz contractions, the maximal isometric force was five times greater than the isotonic load. The rate of phosphorylation was sustained from 4 to 7 s, but the rate of increase in shortening and velocity decreased. The slower rate of change in shortening and velocity may be due to approaching maximal velocity for this short duration of contraction, but is not due to slowing of the rate of phosphorylation of the myosin regulatory light chains.
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PMID:Potentiation of shortening and velocity of shortening during repeated isotonic tetanic contractions in mammalian skeletal muscle. 1188 79


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