The time required to re-establish a functioning endothelial cell layer after vascular implant placement is critical to the success of the respective cardiologic or surgical intervention. Topographic modifications of implant surfaces promise to expedite endothelial regeneration by triggering the activation of cellular machineries that facilitate cell spreading. Exploiting nanoimprint lithography techniques on cyclic olefin copolymer foils, we engineered biocompatible submicron-and micro-structured gratings with groove and ridge width of 1 or 5 mm and groove depth ranging from 0.1 to 2 mm. Our results reveal that both the onset of endothelial spreading and subsequent texture-guided cell polarization critically depend on the feature size of the underlying topography, yet are independently modulated by the surface texture. Specifically, we demonstrate that on gratings with ridge and groove width of 1 mm and groove depth of 1 mm or deeper, the onset of endothelial spreading is 40% faster than on flat substrates, and that the cells align within ten degrees to the gratings. On this topography, we identify two independently regulated phases: acceleration of the onset of spreading supported by the rapid activation of integrin signaling proceeding via Focal Adhesion Kinase, and contact guidance which requires ROCK1/2 and myosin-II dependent cell contractility and focal adhesion maturation.
Aims. The Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter is a hard X-ray imaging spectrometer, which covers the energy range from 4 to 150 keV. STIX observes hard X-ray bremsstrahlung emissions from solar flares and therefore provides diagnostics of the hottest (⪆10 MK) flare plasma while quantifying the location, spectrum, and energy content of flare-accelerated nonthermal electrons.
Methods. To accomplish this, STIX applies an indirect bigrid Fourier imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated CdTe detectors to provide information on angular scales from 7 to 180 arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of STIX has intrinsically low telemetry and it is therefore well-suited to the limited resources available to the Solar Orbiter payload. To further reduce the downlinked data volume, STIX data are binned on board into 32 selectable energy bins and dynamically-adjusted time bins with a typical duration of 1 s during flares.
Results. Through hard X-ray diagnostics, STIX provides critical information for understanding the acceleration of electrons at the Sun and their transport into interplanetary space and for determining the magnetic connection of Solar Orbiter back to the Sun. In this way, STIX serves to link Solar Orbiter’s remote and in-situ measurements.
Phase-contrast imaging at laboratory-based x-ray sources using grating interferometers has been developed over the last few years for x-ray energies of up to 28 keV. Here, we show first phase-contrast projection and tomographic images recorded at significantly higher x-ray energies, produced by an x-ray tube source operated at 100 kV acceleration voltage. We find our measured tomographic phase images in good agreement with tabulated data. The extension of phase-contrast imaging to this significantly higher x-ray energy opens up many applications of the technique in medicine and industrial nondestructive testing.
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