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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