Three-dimensional (3D) printing is a promising technology to develop customized biomaterials in regenerative medicine. However, for the majority of printable biomaterials (bioinks) there is always a compromise between excellent printability of fluids and good mechanical properties of solids. Three-dimensional printing of soft materials based on the transition from a fluid to gel state is challenging because of the difficulties to control such transition as well as to maintain uniform conditions three-dimensionally. To solve these challenges, a facile chemical strategy for the development of a novel hydrogel bioink with shear-thinning and self-healing properties based on dynamic metal–ligand coordination bonds is presented. The noncovalent cross-linking allows easy extrusion of the bioink from a reservoir without changing of its bulk mechanical properties. The soft hydrogel can avoid deformation and collapse using omnidirectional embedding of the printable hydrogel into a support gel bath sharing the same cross-linking chemistry. After combination with photoinitiated covalent cross-linking, it enables manufacturing of hydrogel structures with complex shapes and precise location of chemically attached ligands. Living cells can be entrapped in the new printable hydrogel and survive the following in situ photo-cross-linking. The presented printable hydrogel material expands the existing tool-box of bioinks for generation of in vitro 3D tissue-like structures and direct in vivo 3D printing.

Applying in situ combination of angle-resolved photoemission and inverse photoemission to cleaved III-V compound semiconductor (110) surfaces, we have determined the surface band gaps between the filled anion-derived dangling-bound state A5 and the empty cation-derived state C3 at the I, X ', X, and M points of the surface Brillouin zone. The values of the surface band gaps of the six compounds under study are found to increase in this sequence and seem to be correlated with the fundamental bulk energy gaps. The results are compared with optical surface excitations as well as electron-energy-loss experiments. The low-lying transition energies agree well with our surface band gaps at the X ' and X points.

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Self-assembly is one of the most fascinating phenomena in nature and is one key component in the formation of hierarchical structures. The formation of structures depends critically on the interaction between the different constituents, and therefore the link between these interactions and the resulting structure is fundamental for the understanding of materials. We have realized a two-dimensional system of colloidal particles with tunable magnetic dipole forces. The phase formation is studied by transmission optical microscopy and a phase diagram is constructed. We report a phase transition from hexagonal to random and square arrangements when the magnetic interaction between the individual particles is tuned from antiferromagnetic to ferrimagnetic.

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We report on a normal incidence grating spectrometer for angle-resolved inverse photoemission spectroscopy covering a photon energy range from 10 to 40 eV. Following diffraction from a spherical grating with 201.4 mm radius and 3600 lines/mm the photons are recorded by a position sensitive detector. The compact mounting of the grating and detector on a single 150 mm CF flange is established by displacing detector and sample from the Rowland circle. The performance of the spectrometer concerning energy calibration, spectral efficiency, optical resolution, and count rates was experimentally investigated and found to match the design goals well. Operated together with a low energy electron gun using a low temperature BaO cathode a typical total energy resolution of 360 meV at hν=15 eV is obtained in inverse photoemission spectroscopy. It is shown that due to its compactness the spectrometer unit can be effectively combined with other components for surface analysis.

Low-energy electron diff'raction (LEED) and angle-resolved inverse photoemission spectroscopy (ARIPES) have been applied to the cleaved surface of Bi2Sr2CaCuzOs single crystals. The LEED pattern shows a surface lattice which is identical to the superlattice found in the bulk structure.ARIPES along the I A(a ) direction yields nondispersive unoccupied electronic states at 2.9 and -5 eV above the Fermi energy attributed to Bi-0 derived conduction bands. At about 2 I"X the experimental density of states at the Fermi level increases. This may be due to the crossing of the O(1) band through EF, derived from oxygen atoms in the Cu-0 planes.The recently discovered 83-K superconductor Bi2Sr2-CaCu20s (Ref. 1) has been the subject of many investigations concerning both geometrical ' and electronic " ' structure. While x-ray diffraction and transmission electron diffraction have been used to study the crystal structure of the bulk, the electronic structure has been probed by photoemission spectroscopy (PES), " 's inverse photoemission spectroscopy (IPES), ' x-ray absorption spectroscopy (XAS), ' and electron energy-loss spectroscopy (EELS). ' ' With the exception of EELS these techniques are surface-sensitive spectroscopies. The goal of this study is to investigate the relationship between the bulk and surface structure of single-crystalline Bi2Sr2CaCuz08 using Laue diffraction and low-energy electron diffraction (LEED). We are able to identify the observed LEED spots with highly symmetric directions in the Brillouin zone using a face-centered unit cell in line with recent band-structure calculations. ' The unoccupied part of the band structure has been measured by angle-resolved inverse photoemission spectroscopy (ARIPES) up to 9 eV above the Fermi level along the high-symmetry directions of the Brillouin zone. The preparation of the Bi2Sr2CaCu208 single crystals is described elsewhere.From ac magnetic susceptibility a T, of 83 K is determined. From x-ray diffraction it is concluded that the samples consist dominantly of the n=2 phase.The good chemical stability of the samples is demonstrated by the fact that we did not observe any time dependence of the ARIPES spectra as may be due to, e.g. , oxygen loss. The samples were introduced into an ultrahigh vacuum chamber and cleaved in situ after moderate baking (T 100'C) at a base pressure in the low 10 ' Torr range. The samples had a size of typically 2& 3 mm . Details of the angle-resolved inverse photoemission spectrometer can be found in Refs. 26 and 27.. The photon detector operates at an energy of 9.9 eV, the overall energy resolution of the spectrometer is 640 meV. Wave-vector resolution is estimated to be smaller than 0.1 A '. The Fermi edge of a sputtered polycrystalline gold Alm is used as energy reference. Both LEED and ARIPES measurements have been carried out at room temperatures.Figure 1 (a) shows a Laue photograph obtained by xray back reAection using a Phillips PW 1720 x-ray generator with a tungsten anode at 35 kV. The sample was oriented with the macroscopi...