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Biomedical subjects

U Dahmen

Publications and source records attributed to U Dahmen.

At least 19 recordsLinked to original sources
PubMed2006

Self-assembled nanofold network formation on layered crystal surfaces during metal intercalation.

We study the formation of planar network nanostructures, which develop during metal deposition on initially smooth surfaces of layered compounds. Using in situ low-energy electron microscopy for dynamic observation and high-resolution transmission electron microscopy for structure analysis, we have observed the rapid formation of hexagonal networks of linear "nanofolds" with prismatic cavities on top of layered VSe2 crystals. Their formation results from relaxation of compressive strains which build up during Cu intercalation into a thin surface layer.

Journal Article↗
PubMed2006

The "territorial belonging" of the middle hepatic vein: a troublesome dilemma in adult live donor liver transplantation--anatomical evidence based on virtual 3-dimensional-computed tomography-imaging reconstructions.

BACKGROUND: The venous drainage of the liver plays an essential role in securing viability of both graft and remnant in live donor liver transplantation (LDLT). There is still controversy on whether the middle hepatic vein (MHV) should be routinely included as part of the graft or retained with the remnant liver. The purpose of this study was to analyze hepatic venous drainage patterns based on information obtained by 3-dimensional CT-imaging reconstructions. METHODOLOGY: Fifty five potential live liver donors were evaluated between January 2003 and May 2004 at our Institution. We analyzed two anatomical definitions of liver dominance: total liver dominance (TLD) and hemiliver dominance (HLD). The following concepts were addressed: 1) Hepatic vein territories, 2) Hepatic vein dominance relationship, 3) Territorial belonging- patterns of the MHV to the right and left hemilivers, additionally an analysis of venous outflow in the central liver sectors was performed. RESULTS: Our results showed that: 1) The definitions of dominance: TLD vs. HLD overlap, displaying the MHV belonging, by taking into account the individual right hepatic vein (RHV) variability; 2) A dominant RHV for the whole liver indicates that the RHV is also dominant in the right hemiliver; 3) The MHV belongs predominantly to the left hemiliver (LHL); 4) The left hepatic vein (LHV) is dominant in the LHL. CONCLUSION: Both dominance definitions provide independent mappings of the liver and offer helpful insight into venous dominance relationship.

Adult↗
PubMed2005

Fluctuation of the cytokine expression in the liver during the chronic woodchuck hepatitis virus (WHV) infection is not related to viral load.

The woodchuck together with the woodchuck hepatitis virus (WHV) is an excellent model to study the pathogenesis of hepadnaviral infections. Chronic WHV infection causes severe liver disease and hepatocellular carcinoma in woodchucks. The mechanism of viral clearance is not fully understood, interferons seem to play a major role in down-regulating viral replication prior to elimination of infected hepatocytes. We investigated on the pattern of cytokine and T-cell-marker expression in livers of woodchucks chronically infected with WHV. RNase-protection-assay (RPA) was used to determine mRNA of woodchuck specific genes (TNF-alpha, IFN-gamma, IL-15, CD3, CD4, CD8). Serial liver biopsies were performed daily or weekly in eight chronic WHV-carrier woodchucks. Cytokine/T-cell-marker expression differed significantly between the time points up to +/-50% within each woodchuck. The different expression patterns of cytokines or T-cell-markers did not correlate to the (weak) fluctuations in the viremia but may explain the observed fluctuations in the WHV/HBV-load in chronically infected individuals. Furthermore, we observed associations between cytokine and T-cell-marker expression. The marginal fluctuations in viremia during the chronic infection may indicate, that, once the chronic hepadnaviral infection is established, cytokines/interferons expressed endogenously (i.e. not vector-borne or injected) play only a minor role.

Animals↗
PubMed2004

Carbon nanotubes as nanoscale mass conveyors.

The development of manipulation tools that are not too 'fat' or too 'sticky' for atomic scale assembly is an important challenge facing nanotechnology. Impressive nanofabrication capabilities have been demonstrated with scanning probe manipulation of atoms and molecules on clean surfaces. However, as fabrication tools, both scanning tunnelling and atomic force microscopes suffer from a loading deficiency: although they can manipulate atoms already present, they cannot efficiently deliver atoms to the work area. Carbon nanotubes, with their hollow cores and large aspect ratios, have been suggested as possible conduits for nanoscale amounts of material. Already much effort has been devoted to the filling of nanotubes and the application of such techniques. Furthermore, carbon nanotubes have been used as probes in scanning probe microscopy. If the atomic placement and manipulation capability already demonstrated by scanning probe microscopy could be combined with a nanotube delivery system, a formidable nanoassembly tool would result. Here we report the achievement of controllable, reversible atomic scale mass transport along carbon nanotubes, using indium metal as the prototype transport species. This transport process has similarities to conventional electromigration, a phenomenon of critical importance to the semiconductor industry.

Journal Article↗
PubMed2004

Media remodeling--the result of stent induced media necrosis and repair.

BACKGROUND: Stents have been introduced clinically to help maintaining the patency of the vascular lumen after balloon angioplasty. To ensure a sufficient lumen of the stented vessel, oversized stents are frequently used. However especially deployment of oversized stents may lead to mechanical injury of the intima and media of the vessel wall. The aim of the study was to characterize the vascular lesions and repair processes within the first 4 weeks after implantation of oversized stents in the rabbit carotid artery and thereby contribute to the understanding of vascular remodeling during stent implantation. METHODS: Oversized stents were implanted in the carotid artery of Chinchilla rabbits. Rabbits were sacrificed 3, 7, 14, and 28 days after stent implantation and a detailed histologic and immunohistochemical analysis was performed. RESULTS: The carotid artery was expanded by a factor of 1.3-1.5, leading to a constant dilatation of the vessel. The struts were deeply impressed in the vessel wall, resulting in a disruption of the intima, thrombus formation, media compression and segmental media necrosis. The necrotic media was repopulated by smooth muscle cells by day 7. In contrast to the intima lesions, necrotic areas of the media were not invaded by an inflammatory infiltrate. Formation of neointima, characterized by a confluent layer of endothelial cells and deposition collagenfibers started in close vicinity of the struts. CONCLUSIONS: Being part of a high-pressure system, the arterial vessel apparently adapts to constant dilatation. Deployment of oversized stents caused intima disruption, media necrosis of varying degree and constant dilatation of the vessel wall. Necrosis and repopulation of smooth muscle cells of the media took place within the first 4 weeks, leading to the speculation whether the repopulating SMC are more resistant to the constant pressure.

Animals↗
PubMed2003

Adoptive transfer of donor-derived immunity by liver transplantation: a potential avenue to prevent hepatitis B virus reinfection.

Immunity to hepatitis B has been successfully transferred by bone marrow transplantation, but has also occurred after liver transplantation (LTx). This study was designed to analyse the influence of alloreactivity and immunosuppression, on the efficacy of adoptive immune transfer to hepatitis B by liver transplantation. Orthotopic LTx (n = 34) were performed in three rat strain combinations representing different genetic constellations. Donors had been vaccinated twice with recombinant hepatitis B surface antigen while recipients were unimmunized. Half of the allogeneic recipients were immunosuppressed with cyclosporin A. All animals were monitored weekly for the presence of anti-hepatitis B surface antibodies (anti-HBs). Effective anti-HBs titres were detected in 85% (29/34) of liver recipients and lasted from 2 to 10 weeks. Donor titre above >15 000 mIU/mL ensured a 100% seroconversion rate in the recipients. The maximal anti-HBs titre in recipients represented 0.06% approximately 0.76% of the donor titre. Rejection reduced the adoptive immune transfer, which was protected by immunosuppression. These observations suggest that transfer of functionally active donor lymphocytes, deriving from the graft, contributed to the donor-derived immune response in the recipient. Further studies to augment the donor-derived immune response are warranted to ensure a therapeutic effect for the recipient at risk of reinfection.

Animals↗
PubMed2002

Chevron defect at the intersection of grain boundaries with free surfaces in Au.

We have identified a new defect at the intersection between grain boundaries and surfaces in Au using atomic resolution transmission electron microscopy. At the junction line of 90 degrees <110> tilt grain boundaries of (110)-(001) orientation with the free surface, a small segment of the grain boundary, about 1 nm in length, dissociates into a triangular region with a chevronlike stacking disorder and a distorted hcp structure. The structure and stability of these defects are confirmed by atomistic simulations, and we point out the relationship with the one-dimensional incommensurate structure of the grain boundary.

Journal Article↗
PubMed2002

Electron microscopy observations on the role of twinning in the evolution of microstructures.

Twinning plays an important role in phase transformations and can have significant effects on microstructural evolution. Different roles of twinning in the development of microstructures during precipitation and phase transformations are reviewed and illustrated with examples from investigations by high-resolution electron microscopy, including the effect of multiple twinning on the development of Ge precipitates in Al-Ge and Ag-Ge alloys, the twin dissociation of grain boundaries in Au, the formation of hexagonal Si at twin intersections and the effect of twin boundaries on the equilibrium shape of Pb inclusions in Al.

Alloys↗
PubMed1998

In situ measurement of dihedral angles at liquid grain boundary inclusions.

This work describes experimental aspects of the measurement of relative interfacial energies from the equilibrium dihedral angles of small liquid inclusions or precipitates at interfaces in solids using in situ transmission electron microscopy. We demonstrate how limitations such as faceting, free surfaces, and projection errors can be handled to minimize experimental errors.

Alloys↗
PubMed1998

An in situ nanoindentation specimen holder for a high voltage transmission electron microscope.

We describe in detail, the design, construction, and testing of a specimen holder that allows for the nanoindentation of surfaces while viewing in cross-section in a high voltage transmission electron microscope (TEM). This nanoindentation specimen holder, having three-axis position control of a diamond indenter in combination with micromachined specimens, allows for the first time the dynamic observation of subsurface microstructure evolution under an indenter tip. Additionally, the sample design techniques that have been developed for these procedures may eliminate the need for TEM specimen preparation for additional ex situ nanoindentation experiments. Initial experimental results from in situ indentation of Si samples in the high voltage electron microscope are reported here to demonstrate the capability of this new specimen holder.

Crystallization↗
PubMed1998

In Situ Observations of the Interaction of Liquid Lead Inclusions with Grain Boundaries in Aluminum.

: The evolution of liquid lead (Pb) inclusions at grain boundaries in aluminum (Al) was investigated by direct in situ TEM observation in the temperature range from 330 degrees-643 degreesC. In agreement with earlier reports on quenched alloys, the characteristic contact angle of the lens-shaped grain boundary inclusions was found to be near 120 degrees. This angle remained approximately constant over the entire temperature range, ruling out the possibility of a wetting transition. Coarsening of grain boundary inclusions was observed to proceed mainly by Ostwald ripening, although coalescence could also be observed. Inclusions at grain boundaries, at triple junctions, and at the intersection of grain boundaries with the foil surfaces adopted characteristic shapes that were shown to be equilibrium forms. At the highest temperatures, the grain boundaries were observed to detach from the inclusions and the interaction of a migrating grain boundary with inclusions could be observed.

Journal Article↗
PubMed1998

[Pancreatico-bronchial fistula with communication to a pseudoaneurysm of the arteria lienalis as a rare complication in chronic pancreatitis].

Thoracic manifestations of internal pancreatic fistulas caused by chronic pancreatitis are rare conditions. The three main types of these manifestations are mediastinal pseudocysts, pancreatico pleural fistulas and pancreaticobronchial fistulas. We report on one patient with the clinical presentation of all three thoracic internal pancreatic fistulas with a communication to a pseudoaneurysm of the splenic artery caused by chronic alcohol-related pancreatitis. Conservative therapy over four weeks was not successful. Resection of the pseudoaneurysm, debridement of the mediastinal pseudocyst and duodenum preserving resection of the pancreas treated all complications and prevents recurrence in this patient with chronic pancreatitis.

Adult↗
PubMed1995

Patterns of inflammatory vascular endothelial changes in murine liver grafts.

We have investigated the vascular endothelial phenotypes found at various times posttransplant in murine B10-->C3H liver grafts. In this model, liver allografts are spontaneously accepted, and survive indefinitely unless the recipient is first allosensitized with a skin allograft, in which case the liver allografts are rejected within five days. In our previous studies, allograft inflammation was associated with the development of vascular endothelial reactivity with the mAbs MECA-32 and M/K-2 (anti-VCAM-1). We observed that vascular endothelia in both liver isografts and allografts develop reactivity with MECA-32 mAb within two days of transplantation, indicating endothelial activation in both situations. In contrast, only the endothelia in liver allografts develop VCAM-1 expression, as detected with M/K-2 mAb. VCAM-1 was expressed in both rejecting and accepting liver allografts, demonstrating that endothelial VCAM-1 expression is indicative of ongoing graft inflammation but not necessarily graft rejection. Liver parenchymal cells did not appear to develop reactivity with either antibody under any of the conditions tested. In contrast, bile duct epithelia developed M/K-2 reactivity (VCAM-1 expression), but not MECA-32 reactivity in liver allografts, but not isografts. These data demonstrate alloantigen-dependent and alloantigen-independent patterns of endothelial behavior in murine liver grafts that are quite similar to those found in murine cardiac grafts. Further, they demonstrate that the expression of VCAM-1 by graft endothelia is not diagnostic for acute rejection of liver allografts.

Animals↗