Surface morphology of as grown and annealed bulk GaN crystals

GaN single crystals have been grown from Ga solution. The crystals grow in the form of platelets with their basal plane perpendicular to the c-axis. The two opposite crystal surfaces are not equivalent since one is N- and the other Ga-terminated. Atomic force microscopy has been applied to study surface morphology on both surfaces. It was found that one side is atomically flat. The other side consists of pyramid-like structures about 25 nm in size.

The influence of annealing in an NH3+H2 atmosphere in the temperature range from 600°C to 900°C was investigated. Depending on crystal face the results were drastically different. It was found that on the rough side, annealing yields an atomically flat surface with terraces of monolayer height. The size of the terraces depends on the temperature of the annealing. On the originally flat side the surface becomes rougher after annealing. The transformation of surface morphology begins at temperatures below 700°C. Preliminary results of annealing in a hydrogen atmosphere are also reported. These findings are crucial for the understanding and development of GaN homoepitaxy.

Membrane cut-off does not influence results regarding the measurement of small molecules - a comparative study between 20- and 100-kDa catheters in hepatic microdialysis

BACKGROUND

Microdialysis is a method used to monitor hepatic tissue metabolism. Membranes with a molecular cut-off of 20 kilodalton (kDa) are currently used to measure the small metabolites glucose, glycerol, lactate and pyruvate. Using membranes with higher cut-off such as 100 kDa allows the possibility of measuring larger molecules but may affect results regarding small molecules. The aim was to compare microdialysis catheters with a cut-off of 20 and 100 kDa in the measurement of small molecules in a pig liver model.

METHODS

Four microdialysis catheters were inserted into the liver of each pig used in the experiment (n = 6). Two catheters with cut-off of 20 kDa were perfused with Ringer acetate, and two catheters with cut-off of 100 kDa: one perfused with Ringer acetate and one with hydroxyethyl starch (Voluven) at a flow rate of 0·3 μl min(-1). Dialysate samples were collected at 40-min intervals and analysed for glucose, glycerol, lactate and pyruvate.

RESULTS

Compared to the other catheters, the 100-kDa catheters perfused with Ringer acetate tended to measure higher dialysate concentrations of the small molecules, the difference reaching statistical significance in the case of pyruvate. Concentrations measured by the 100-kDa catheters perfused with Voluven were, however, comparable to the 20-kDa catheters.

CONCLUSIONS

Microdialysis catheters with membrane cut-off of 20 and 100 kDa can be used equally in hepatic microdialysis for the monitoring of glucose, glycerol, lactate and pyruvate, and lactate/pyruvate ratio if a high osmotic solution (Voluven) is used to perfuse the 100-kDa catheters.

Involvement of the monoaminergic system in the antidepressant-like activity of chromium chloride in the forced swim test

Bio-metal chromium(III) is a crucial microelement for the proper functioning of living organisms. Previous preclinical and clinical studies reported its potential antidepressant properties. The aim of the present study was to examine the effect of antidepressants and noradrenergic and dopaminergic receptor antagonists on chromium chloride (CrCl₃) activity in the forced swim test (FST) in mice and rats. Imipramine (5 mg/kg), fluoxetine (5 mg/kg) and reboxetine (5 mg/kg) but not bupropion (1 mg/kg), administered jointly with CrCl₃ at a dose of 6 mg/kg, reduced the immobility time in the FST in mice. The reduction of the immobility time induced by the active dose (12 mg/kg) of CrCl₃ was completely abolished by propranolol (2 mg/kg, β-adrenoceptor antagonist), SCH 23390 (0.5 mg/kg, a dopamine D₁ receptor antagonist), and partially by prazosin (1 mg/kg, an α₁-adrenoceptor antagonist), yohimbine (1 mg/kg, an α₂-adrenoceptor antagonist) and sulpiryd (50 mg/kg, a dopamine D₂/D₃ receptor antagonist) administration. The locomotor activity was significantly reduced by CrCl₃ + reboxetine treatment, which did not influence the reboxetine enhancement of the antidepressant-like effect of CrCl₃ in the FST. Moreover, CrCl₃ at a dose of 32 mg/kg (although not at 12 mg/kg) significantly reduced the immobility and enhanced the climbing (but not swimming) time in the FST in rats, which indicates the involvement of the noradrenergic pathway in this effect. The present study indicates that the antidepressant-like activity of chromium in the FST is dependent (although to a different extent) on the noradrenergic, dopaminergic and serotonin systems.

Hepatocyte transplantation for inherited metabolic diseases of the liver

Inherited metabolic diseases of the liver are characterized by deficiency of a hepatic enzyme or protein often resulting in life-threatening disease. The remaining liver function is usually normal. For most patients, treatment consists of supportive therapy, and the only curative option is liver transplantation. Hepatocyte transplantation is a promising therapy for patients with inherited metabolic liver diseases, which offers a less invasive and fully reversible approach. Procedure-related complications are rare. Here, we review the experience of hepatocyte transplantation for metabolic liver diseases and discuss the major obstacles that need to be overcome to establish hepatocyte transplantation as a reliable treatment option in the clinic.

The circulating platelet count is not dictated by the liver, but may be determined in part by the bone marrow: analyses from human liver and stem cell transplantations

BACKGROUND

The platelet count varies considerably between individuals, but within an individual the platelet count is remarkably stable over time. Mechanisms controlling the platelet count are not yet established.

OBJECTIVE

In the present study, we tested the hypothesis that the liver is important in controlling the circulating platelet count, as the liver is the main producer of thrombopoietin.

METHODS

We compared the platelet count prior to and after liver transplantation in >250 patients transplanted for familial amyloidotic polyneuropathy (FAP). In contrast to most patients undergoing liver transplantation, patients with FAP have normal liver function before transplantation. Furthermore, we compared platelet counts in 89 living liver donors with the platelet count in the recipients of these grafts. Finally we compared platelet counts in donor-recipient pairs of hematopoietic stem cells.

RESULTS AND CONCLUSIONS

The platelet count prior to transplantation correlated with the platelet count at 3 or 12 months after transplantation in patients with FAP (r=0.48, P<0.0001 at 3 months, r=0.39, P<0.0001 at 12 months), whereas the platelet count in a living liver donor did not correlate with the platelet count in the recipient at 3 or 12 months after transplantation (r=0.16, P=0.26 at 3 months, r=0.11, P=0.30 at 12 months). The platelet count of related donors of hematopoietic stem cells correlated with the platelet count in the recipient after transplantation (r=0.25, P=0.011).

CONCLUSIONS

These results suggest that the liver, in spite of being the prime producer of thrombopoietin, does not dictate the circulating platelet count, whereas the bone marrow does appear to play a role.

Oxygen-charged HTK-F6H8 emulsion reduces ischemia-reperfusion injury in kidneys from brain-dead pigs

BACKGROUND

Prolonged cold ischemia is frequently associated with a greater risk of delayed graft function and enhanced graft failure. We hypothesized that media, combining a high oxygen-dissolving capacity with specific qualities of organ preservation solutions, would be more efficient in reducing immediate ischemia-reperfusion injury from organs stored long term compared with standard preservation media.

METHODS

Kidneys retrieved from brain-dead pigs were flushed using either cold histidine-tryptophan-ketoglutarate (HTK) or oxygen-precharged emulsion composed of 75% HTK and 25% perfluorohexyloctane. After 18 h of cold ischemia the kidneys were transplanted into allogeneic recipients and assessed for adenosine triphosphate content, morphology, and expression of genes related to hypoxia, environmental stress, inflammation, and apoptosis.

RESULTS

Compared with HTK-flushed kidneys, organs preserved using oxygen-precharged HTK-perfluorohexyloctane emulsion had increased elevated adenosine triphosphate content and a significantly lower gene expression of hypoxia inducible factor-1α, vascular endothelial growth factor, interleukin-1α, tumor necrosis factor-α, interferon-α, JNK-1, p38, cytochrome-c, Bax, caspase-8, and caspase-3 at all time points assessed. In contrast, the mRNA expression of Bcl-2 was significantly increased.

CONCLUSIONS

The present study has demonstrated that in brain-dead pigs the perfusion of kidneys with oxygen-precharged HTK-perfluorohexyloctane emulsion results in significantly reduced inflammation, hypoxic injury, and apoptosis and cellular integrity and energy content are well maintained. Histologic examination revealed less tubular, vascular, and glomerular changes in the emulsion-perfused tissue compared with the HTK-perfused counterparts. The concept of perfusing organs with oxygen-precharged emulsion based on organ preservation media represents an efficient alternative for improved organ preservation.

Fabrication of corrugated Ge-doped silica fibers

We present a method of fabricating Ge-doped SiO2 fibers with corrugations around their full circumference for a desired length in the longitudinal direction. The procedure comprises three steps: hydrogenation of Ge-doped SiO2 fibers to increase photosensitivity, recording of Bragg gratings with ultraviolet light to achieve modulation of refractive index, and chemical etching. Finite-length, radially corrugated fibers may be used as couplers. Corrugated tapered fibers are used as high energy throughput probes in scanning near-field optical microscopy.

Improving the techniques for human hepatocyte transplantation: report from a consensus meeting in London

On September 6 and 7, 2009 a meeting was held in London to identify and discuss what are perceived to be current roadblocks to effective hepatocyte transplantation as it is currently practiced in the clinics and, where possible, to offer suggestions to overcome the blocks and improve the outcomes for this cellular therapy. Present were representatives of most of the active clinical hepatocyte transplant programs along with other scientists who have contributed substantial basic research to this field. Over the 2-day sessions based on the experience of the participants, numerous roadblocks or challenges were identified, including the source of cells for the transplants and problems with tracking cells following transplantation. Much of the discussion was focused on methods to improve engraftment and proliferation of donor cells posttransplantation. The group concluded that, for now, parenchymal hepatocytes isolated from donor livers remain the best cell source for transplantation. It was reported that investigations with other cell sources, including stem cells, were at the preclinical and early clinical stages. Numerous methods to modulate the immune reaction and vascular changes that accompany hepatocyte transplantation were proposed. It was agreed that, to obtain sufficient levels of repopulation of liver with donor cells in patients with metabolic liver disease, some form of liver preconditioning would likely be required to enhance the engraftment and/or proliferation of donor cells. It was reported that clinical protocols for preconditioning by hepatic irradiation, portal vein embolization, and surgical resection had been developed and that clinical studies using these protocols would be initiated in the near future. Participants concluded that sharing information between the groups, including standard information concerning the quality and function of the transplanted cells prior to transplantation, clinical information on outcomes, and standard preconditioning protocols, would help move the field forward and was encouraged.

Structural and Optical Properties of Homoepitaxial GaN Layers

The review of structural and optical properties of homoepitaxial layers grown by MOVCD on single crystals GaN substrates is presented. The TEM technique is used to characterise the structural properties of epi-layers. It is found that the structural properties of GaN homoepitaxial layers are determined by the polarity of the substrate surface on which the growth takes place. It is shown that threading dislocations are present only in the layers grown on the [0001] “smooth” surface. On the other hand the layers grown on the [0001] “rough” surface are free from vertical defects. The characteristic feature of the growth on the “rough” surface are pinholes. The optical properties of homoepitaxial layers are predominantly determined by the growth polarity as well. It is shown also that the reflectivity measurement is the most precise way to determine the exciton energies and that emissions due to free excitons are strongly affected by polariton effects.

Fine-tuning of the spin-density-wave state in Cr/V heterostructures via hydrogen uptake

We show that the magnetic state in rather thick Cr films can be finely tuned via hydrogen uptake into adjacent vanadium layers at rather low hydrogen pressures. By changing the hydrogen concentration and, hence, the electronic structure in the V layers, it is possible to affect the global properties of spin-density waves (SDWs) in Cr layers, including the SDW period and the Néel temperature. We provide direct experimental evidence that hydrogen uptake into V layers can be used to switch between incommensurate and commensurate SDW states in a reproducible way.

[New anticoagulants for secondary haemostasis--anti IIa inhibitors]

In contrast to heparins and oral anticoagulants, anti IIa inhibitors (thrombin inhibitors) are able to directly inhibit the protease activity of thrombin and can thereby precisely control the blood coagulation process. Direct thrombin inhibitors are either biosimilars (r-hirudin) or synthetically produced substances (bivalirudin, argatroban, dabigatran). In 1997 r-hirudin was introduced into clinical practice, however due to its narrow therapeutic range and the necessity of drug monitoring it has not gained widespread clinical use by now. Since 2004 and 2005 the synthetic thrombin inhibitors bivalirudin and argatroban, respectively, are available. With dabigatran the first oral synthetic thrombin inhibitor followed in 2008. These four drugs can inhibit even clot bound thrombin and show low plasma protein binding. They differ in respect to route and duration of application as well as elimination from the body, thereby offering a precise inhibition of blood coagulation adjusted to the individual case and without danger of HIT II. These advantages shall be used and advanced by the development of further direct thrombin inhibitors.