Biomedical subjects
Publications and source records attributed to U Dahmen.
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.
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.
: 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.
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.
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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.
A two-stage jet polishing technique is described which, utilising the effects of the characteristic current-voltage behaviour of electropolishing solutions, can produce excellent TEM foils of relatively coarse two-phase materials.
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Spontaneous orthotopic liver allograft acceptance associated with microchimerism in mice induces tolerance to subsequent skin or heart transplants from the donor but not third-party animals. Despite in vivo hyporesponsiveness, in vitro MLC and CTL assays showed continuing antidonor reactivity. Cells isolated from recipients' spleens and grafted livers, when tested in MLC and CTL assays, were antidonor reactive out to 3 months to the same degree as splenocytes obtained from either naive or presensitized (with skin or heart) mice. Nevertheless, passive transfer of splenocytes or liver lymphocytes from liver tolerant mice, but not naive or sensitized donor strain mice, were able to prolong skin graft survival significantly in naive irradiated recipients. By using a strain combination in which the donor but not the recipient expressed the stimulatory endogenous super-Ag (Mlsf), it was possible to determine whether super-Ag-reactive T cells bearing V beta 5 and V beta 11 were deleted or anergic. Phenotypic analysis of cells isolated from recipients' spleens and grafted livers (up to 90 days after transplant), when compared with naive animals, showed no significant difference in V beta 5 and V beta 11 TCR expression. Additionally, when these isolated spleen cells were tested for antibody-mediated stimulation, both anti-V beta 5 and V beta 11 TCR mAb led to marked proliferation of cells obtained from naive and liver-transplanted recipients, but as expected, proliferation was very low in cells from naive donors. These results suggest that liver transplantation induces donor-specific tolerance in vivo, which may not be reflected in in vitro proliferative and cytotoxicity assays (split tolerance). Furthermore, this tolerance does not seem to be induced by clonal deletion or anergy of minor-lymphocyte-stimulating-antigen-reactive T cells in the recipients.
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After a 5 years' experience of cerebral sonography (about 4,500 recordings) in infants we are trying to establish correlations between alterations of anatomical structures and the further clinical development. Obviously there is no constant connexion between a simple subependymal haemorrhage and the further neurological symptoms. At the age of two and more years, about 30% had a normal state, the other part had very different clinical signs. Even an uncomplicated ventricular haemorrhage had no definite influence on the child's development in most cases. Ischemic infarctions seem to have a better prognosis than borderline-infarctions. Real intracranial cysts and slight brain atrophy seem to have only distinct neurological symptoms. Porencephalic defects or brain necrosis, e.g. after parenchymatous haemorrhages and infarctions as well as generalized hypoxic encephalopathies with increased echogenicy and progressive brain atrophy nearly always showed neurological defects, though the dimension of the brain's alteration does not clearly correlate to the clinical symptoms and the child's development. It is not possible to make a prognostic evaluation by cerebral sonography in hypoxic-ischemic brain-lesions within the first 3 weeks post partum. A more exact judgement will be given after further regular sonographic observations in all high-risk infants within the first year. Beyond this, technical and organisation-improvements will probably allow a more exact statement in future.