Bioenergetics of contracting skeletal muscle after partial reduction of blood flow

The purpose of this study was to examine the bioenergetics and regulation of O2 uptake (VO2) and force production in contracting muscle when blood flow was moderately reduced during a steady-state contractile period. Canine gastrocnemius muscle (n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s (Hz) immediately followed by a reduction of blood flow [ischemic (I) condition] to 46 +/- 3% of the value obtained at 0.5 Hz with normal blood flow. The VO2 of the contracting muscle was significantly (P < 0.05) reduced during the I condition [6.5 +/- 0.8 (SE) ml . 100 g-1 . min-1] compared with the same stimulation frequency with normal flow (11.2 +/- 1.5 ml . 100 g-1 . min-1), as was the tension-time index (79 +/- 12 vs. 123 +/- 22 N . g-1 . min-1, respectively). The ratio of VO2 to tension-time index remained constant throughout all contraction periods. Muscle phosphocreatine concentration, ATP concentration, and lactate efflux were not significantly different during the I condition compared with the 0. 5-Hz condition with normal blood flow. However, at comparable rates of VO2 and tension-time index, muscle phosphocreatine concentration and ATP concentration were significantly less during the I condition compared with normal-flow conditions. These results demonstrate that, in this highly oxidative muscle, the normal balance of O2 supply to force output was maintained during moderate ischemia by downregulation of force production. In addition, 1) the minimal disruption in intracellular homeostasis after the initiation of ischemia was likely a result of steady-state metabolic conditions having already been activated, and 2) the difference in intracellular conditions at comparable rates of VO2 and tension-time index between the normal flow and I condition may have been due to altered intracellular O2 tension.     

Degradation and drug‐release studies of a poly(glycolide‐co‐trimethylene carbonate) copolymer (Maxon)

Poly(glycolide‐co‐trimethylene carbonate) is available commercially as a monofilament suture known as Maxon. The literature has shown that Maxon sutures possess a slow degradation rate of about 7 months and exhibit relatively high mechanical strength in comparison with other absorbable sutures. However, very few articles are available on the degradation of unoriented Maxon. This study was designed to explore the chemical and physical aspects of the degradation of unoriented Maxon and its potential as a drug‐release device. Several analytical techniques were used, including mass measurements, simultaneous small‐angle X‐ray scattering and wide‐angle X‐ray scattering, and thermoporometry. Magnetic resonance imaging and drug‐release measurements were carried out with UV spectroscopy. The results suggest that unoriented suture‐based Maxon undergoes multiple stages of hydrolytic degradation, which involve hydration, and active and postactive periods. The drug‐release mechanism is controlled by diffusion in the early degradation stages and polymer erosion in the later stages of release. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 475–486, 2005     

Polarisation enhanced C magnetic resonance studies of the hydrogenation of pentene over Pd/Al2O3 catalysts

This paper reports the first demonstration of ¹³C distortionless enhancement by polarisation transfer (DEPT) NMR spectroscopy at natural abundance to study the hydrogenation and isomerisation of pentenes over a 1 wt% Pd/Al₂O₃ catalyst. Single component C5 hydrocarbons and binary mixtures of hydrocarbon and hydrogen have been adsorbed on both a pure alumina support and the Pd/Al₂O₃ catalyst derived from it. The pentene species studied were 1-, cis-2- and trans-2-pentene. No isomerisation or hydrogenation was observed when single component pentene isomers or binary mixtures of 1-pentene and hydrogen, and cis-2-pentene and hydrogen were adsorbed onto the pure alumina support. However, when trans-2-pentene and hydrogen were both adsorbed onto the support, partial hydrogenation to n-pentane was observed in addition to the presence of both cis-2- and trans-2-pentenes. All pentene isomers hydrogenate over the Pd/Al₂O₃ catalyst to give predominantly n-pentane and a small amount of the trans-2-pentene isomer. For the parameters chosen here these studies show that trans-2-pentene appears to be the active isomer for hydrogenation over the pure support alone.     

Manipulation and tracking of superparamagnetic nanoparticles using MRI

The use of magnetic fields in magnetic resonance imaging (MRI) for the tracking and delivery of chemotherapeutics bound to superparamagnetic nanoparticles offers a promising method for the non-invasive treatment of inoperable tumours. Here we demonstrate that superparamagnetic magnetite nanoparticles fabricated by an easily scalable method can be driven and tracked in real time at high velocities in vitro using MRI hardware. Force balance calculations are consistent with the magnetic properties of individual 10 nm diameter particles that move collectively as micron sized agglomerates with hydrodynamic diameter similar to that inferred from zero-magnetic-field dynamic light scattering measurements.     

Terahertz time-domain spectroscopy and the quantitative monitoring of mechanochemical cocrystal formation

Terahertz (THz) radiation probes intermolecular interactions through crystal lattice vibrations, allowing the characterization of solid materials. Thus, THz spectroscopy is a promising alternative to mainstream solid-state analytical tools such as X-ray diffraction or thermal analysis. The method provides the benefits of online measurement, remote sampling and three-dimensional imaging, all of which are attractive for quality control and security applications. In the context of pharmaceutical solids, THz spectroscopy can differentiate and quantify different forms of active pharmaceutical ingredients. Here, we apply this technique to monitor a dynamic process involving two molecular crystals. In particular, we follow the mechanochemical construction of a two-component cocrystal by grinding together phenazine (phen) and mesaconic acid (mes). To rationalize the observed changes in the spectra, we conduct lattice dynamics calculations that lead to the tentative assignment of at least one feature in the cocrystal THz spectrum.     

Spatially resolved measurement of anisotropic granular temperature in gas-fluidized beds

This paper reports the measurement of granular temperature in gas-fluidized beds using magnetic resonance. Experiments were performed using 0.5 and 1.2 mm diameter particles (Geldarts group B and D) in both a 3-dimensional cylindrical bed and a 2-dimensional rectangular bed. Measurements were performed over a range of motion encoding times to confirm that the experiments were in the ballistic regime. The results confirm that the granular temperature arises from shear induced by the bubble motion. It was found that the hydrodynamics in the 2D and 3D geometries were significantly different with lower bubble velocities but a higher bubble temperature in the 2D bed than in the 3D bed. The granular temperature was also found to be highly anisotropic, with T_z up to 10 times greater than T_x or T_y.     

A carpet cloak for visible light

We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n<1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies.     

Methylmercury formation in a wetland mesocosm amended with sulfate

This study used an experimental model to evaluate methylmercury accumulation when the soil of a constructed wetland is amended with sulfate. The model was planted with Schoenoplectus californicus and designed to reduce wastestream metals and metal-related toxicity. The soil was varied during construction to provide a control and two sulfate treatments which were equally efficient at overall mercury and copper removal. After an initial stabilization period, methylmercury concentrations in porewater were up to three times higher in the sulfate-treated porewater (0.5-1.6 ng/L) than in the control (<0.02-0.5 ng/L). Mean percent methylmercury was 9.0% in the control with 18.5 and 16.6% in the low- and high-sulfate treatments, respectively. Methylmercury concentrations measured in mesocosm surface water did not reflect the differences between the control and the sulfate treatments that were noted in porewater. The mean bulk sediment methylmercury concentration in the top 6 cm of the low-sulfate treatment (2.33 ng/g) was significantly higher than other treatment means which ranged from 0.96 to 1.57 ng/g. Total mercury in sediment ranged from 20.8 to 33.4 ng/g, with no differences between treatments. Results suggest that the non-sulfate-amended control was equally effective in removing metals while keeping mercury methylation low.     

The Degradation of Polyglycolide in Water and Deuterium Oxide. Part II: Nuclear Reaction Analysis and Magnetic Resonance Imaging of Water Distribution

Magnetic resonance imaging (MRI) and scanning microbeam nuclear reaction analysis (NRA) were used to monitor changes of water ingress into polyglycolide (PGA) disks with degradation time. MRI detects H₂O, whereas NRA is sensitive to D₂O. The acid-catalysed hydrolysis of the ester is significantly slower in D₂O than H₂O because of the kinetic isotope effect. This behaviour was investigated in Part I. In this paper, NRA was used to investigate PGA hydration in buffers made from D₂O, and NRA and MRI experiments were performed on samples degraded buffers made from a 50% mixture of D₂O and H₂O (D₂O/H₂O 50:50) to allow a comparison between the two techniques. The NRA and MRI results provide direct evidence in support of the four-stage reaction-erosion model reported in previous literature, and show that this model applies to polymer degradation in heavy water and in a buffer made from D₂O/H₂O 50:50. It is believed that this is the first time that NRA and MRI have been compared for the same hydrating system.     

Imaging droplet freezing using MRI

Magnetic resonance imaging (MRI) is used to provide spatially resolved structural and chemical composition characterisation of droplets undergoing freezing. To this end, MRI is applied to a diameter sucrose solution droplet, suspended in cold air. During the consequential solidification of the droplet, the spatial location of nucleation and the crystal growth of the droplet are followed using non-invasive two dimensional (2D) images; these are produced using the fast MRI technique, RARE. This is able to both quantify crystal growth rates, as well as the unfrozen liquid mass fraction for the optically opaque freezing droplets. Such information is of major interest in the verification of models describing the freezing of such droplets. The spatial re-distribution of the sucrose solute as a consequence of freezing is monitored using MR 1D chemical shift profiling. The formation of a concentrated sucrose layer at the droplet surface was detected.