Anke Aretz

Ultrastructural Analysis of Vascular Calcifications in Uremia

Accelerated intimal and medial calcification and sclerosis accompany the increased cardiovascular mortality of dialysis patients, but the pathomechanisms initiating microcalcifications of the media are largely unknown. In this study, we systematically investigated the ultrastructural properties of medial calcifications from patients with uremia. We collected iliac artery segments from 30 dialysis patients before kidney transplantation and studied them by radiography, microcomputed tomography, light microscopy, and transmission electron microscopy including electron energy loss spectrometry, energy dispersive spectroscopy, and electron diffraction. In addition, we performed synchrotron x-ray analyses and immunogold labeling to detect inhibitors of calcification. Von Kossa staining revealed calcification of 53% of the arteries. The diameter of these microcalcifications ranged from 20 to 500 nm, with a core-shell structure consisting of up to three layers (subshells). Many of the calcifications consisted of 2- to 10-nm nanocrystals and showed a hydroxyapatite and whitlockite crystalline structure and mineral phase. Immunogold labeling of calcification foci revealed the calcification inhibitors fetuin-A, osteopontin, and matrix gla protein. These observations suggest that uremic microcalcifications originate from nanocrystals, are chemically diverse, and intimately associate with proteinaceous inhibitors of calcification. Furthermore, considering the core-shell structure of the calcifications, apoptotic bodies or matrix vesicles may serve as a calcification nidus.

Analysis of Calcifications in Patients with Coral Reef Aorta

BACKGROUND Coral reef aorta is a rare vascular disease with intraluminal calcifications of the dorsal part of the visceral aorta. The pathogenesis of this disease with its topographic and morphologic characteristics is unknown. The aim of our study was to investigate calcification inhibitors and the ultrastructure of calcifications in patients with coral reef aorta. METHODS Ten patients with coral reef aorta were examined. Calcified specimens were investigated by immunohistochemical techniques for the expression of the calcification inhibitors matrix gla protein (MGP) and fetuin-A. Vessel walls were also assessed by electron microscopic techniques including electron energy-lost spectroscopy, electron dispersive spectroscopy, and electron diffraction. Sera of patients were analyzed for fetuin-A, uncarboxylated MGP (ucMGP), and osteoprotegerin. RESULTS As assessed by immunohistochemistry, most MGP was detected in the vicinity of calcified regions. Serum levels of the calcification inhibitors ucMGP, fetuin-A, and osteoprotegerin were 370+/-107 nmol/L, 0.57+/-0.03 g/L, and 5.64+/-0.79 pmol/L, respectively. Ultrastructural analysis of calcified specimens showed a core-shell structure with multiple calcification nuclei. Calcifications displayed a fine-crystalline character, and elemental analysis revealed hydroxyl apatite as the chemical compound. CONCLUSION The coral reef aorta represents an extreme exophytic growth of vascular calcification with multiple nuclei which resemble typical media calcification. Positive vascular immunostaining and low serum levels of both fetuin-A and ucMGP suggest a pathophysiologic role of these calcification inhibitors in the development of coral reef aorta.

Failure Initiation in Dual-Phase Steel

This research work aims to model the failure initiation in dual-phase (DP) steel. A microstructure based approach by means of representative volume elements (RVE) is employed to evaluate the microstructure deformation and the failure initiation on the mesoscale. In order to determine cohesive parameters for martensite cracking, a two level approach has been performed experimentally. First, in-situ bending test in SEM with EBSD measurements before and after the test showed that the crack initiation occurs in martensite islands. Then, mini tensile tests with DIC technique were carried out to identify macroscopic failure initiation strain values. RVE modeling combined with extended finite element method (XFEM) was utilized to model martensite cracking on mesoscale. The identified parameters were validated by comparing the predictions with the experimental results.

Application of sputter-assisted EPMA to depth profile analysis

Abstract. A common problem in depth profile measurement is the calibration of the depth scale. The new technique of sputter assisted electron probe microanalysis offers the possibility of calculating the composition as well as the depth scale solely from the acquired X-ray intensity data without further information, e.g. sputter rates. To achieve a depth resolution that is smaller than the depth of information of the electron probe, i.e. 0.1–1 μm, special deconvolution algorithms must be applied to the acquired data.To assess the capabilities of this new technique it was applied to a Ti/Al/Ti multilayer on Si under different measurement conditions. Quantitative depth profiles were obtained by application of a deconvolution algorithm based on maximum entropy analysis. By comparison of these profiles with AES depth profiles and AFM roughness measurements, it was shown that the limiting factor to the achievable depth resolution is the occurrence of surface roughening induced by the sputtering process rather than the relatively large depth of information of the electron probe.We conclude that for certain applications sputter-assisted EPMA can be regarded as a valid depth profiling technique with a depth resolution in the nm range.

Nanomechanical and analytical investigations of tribological layers for wear protection in slow-running roller bearings

In a tribological system consisting of roller thrust bearings and various lubricants, we investigated reaction layers formed in the presence of lubricants with low wear protection, high wear and fatigue protection as well as high wear but low fatigue protection. The bearings were tested under heavy-duty conditions in an FE-8 test rig in order to rapidly asses the efficiency of different reaction layer systems. Chemical composition and microstructure analysis of the layers was subsequently carried out by transmission electron microscopy on thin cross-sections prepared by the focused ion beam technique. The nanomechanical properties of the different tribological layers were analyzed by nanoindentation. The formation and structure of the layered system, and thus the ability to protect against wear and fatigue, depends on the lubricants and additives, respectively. Our results indicate that wear protection not only relies on the reaction layer itself but also on the properties of the combined system of the reaction layer and an underlying tribomutation layer.