The development of a multimaterial extrusion bioprinting platform is reported. This platform is capable of depositing multiple coded bioinks in a continuous manner with fast and smooth switching among different reservoirs for rapid fabrication of complex constructs, through digitally controlled extrusion of bioinks from a single printhead consisting of bundled capillaries synergized with programmed movement of the motorized stage.

The emerging properties of noble metal nanoparticles are attracting huge interest from the translational scientific community. In this feature article, we highlight recent advances in the adaptation of noble metal nanomaterials and their biomedical applications in therapeutics, diagnostics and sensing.

Self-healing materials are an emerging class of modern materials gaining importance due to environmental and energy concerns. Materials based on the complexation of oppositely charged polyelectrolytes, usually in the form of coatings and films, have been shown to have water activated self-healing properties. In this work, the self-healing of bulk branched poly(ethylene imine) and poly(acrylic acid) (BPEI/PAA) complex is studied as a function of the aqueous solutions used to activate the self-healing. Specifically, exposure to different salt solutions and solutions of different pH was examined including sodium and copper ion containing solutions as well as acidic and basic solutions. By applying NaCl treatment, especially followed by exposure to DI water, the self-healing ability of the BPEI/PAA complex was enhanced. In contrast, after treated by CuCl, the BPEI/PAA complex lost its self-healing ability, showing an ability to modulate the ability to self-heal as a function of external stimulus. In addition to improving the ability to self-heal using salt as compared to using DI water alone, acidic and basic solutions can also improve the ability to self-heal. The self-healing is caused by chain mobility at the cut interface of the polyelectrolyte complex material which is controlled by charge density along the polyelectrolyte backbone as well as ionic cross-link density, and correlation between this mobility to rheological behavior is made. Tensile testing and determination of fracture toughness were used to characterize self-healing.

2,2'-Bipyridine (bpy), 1,10-phenanthroline (phen) and related bidentate ligands often inhibit homogeneous Pd-catalyzed aerobic oxidation reactions; however, certain derivatives, such as 4,5-diazafluoren-9-one (DAF), can promote catalysis. In order to gain insight into this divergent ligand behavior, eight different bpy- and phen-derived chelating ligands have been evaluated in Pd(OAc)2-catalyzed oxidative cyclization of (E)-4-hexenyltosylamide. Two of the ligands, DAF and 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me2bpy), support efficient catalytic turnover, while the others strongly inhibit the reaction. DAF is especially effective and is the only ligand that exhibits “ligand-accelerated catalysis”. Evidence suggests that the utility of DAF and 6,6'-Me2bpy originates from the ability of these ligands to access κ1-coordination modes via dissociation of one of the pyridyl rings. This hemilabile character is directly observed by NMR spectroscopy upon adding one equivalent of pyridine to solutions of 1:1 L/Pd(OAc)2 (L = DAF and 6,6'-Me2bpy), and is further supported by an X-ray crystal structure of Pd(py)(κ1-DAF)OAc2. DFT computational studies illuminate the influence of three different chelating ligands [DAF, 6,6'-Me2bpy, and 2,9-dimethyl-1,10-phenanthroline (2,9-Me2phen)] on the energetics of the aza-Wacker reaction pathway. The results show that DAF and 6,6'-Me2bpy destabilize the corresponding ground-state Pd(N~N)(OAc)2 complexes, while stabilizing the rate-limiting transition state for alkene insertion into a Pd–N bond. Interconversion between κ2- and κ1-coordination modes facilitate access to open coordination sites at the PdII center. The insights from these studies introduce new ligand concepts that could promote numerous other classes of Pd-catalyzed aerobic oxidation reaction.

Slippery liquid-infused porous surfaces (SLIPS) have potential impact on a wide range of industries, including healthcare, food packaging, and automobile. A tremendouseffort has been focused on developing novel fabrication methods for making SLIPS. However, current fabrication methods usually involve harsh conditions and complicated postfabrication modifications or are limited to specific substrates. Presented here is a novel method for the fast and facile fabrication of SLIPS. Layer-by-layer (LBL) assembly of branched polyethylenimine and Nafion, a perfluorinated polyelectrolyte, is performed with methanol as the solvent. Hierarchically rough and superhydrophobic surface is obtained directly without further modification on various substrates. The surface properties are shown to highly depend on the LBL assembly parameters, including deposition cycles, dipping time, rinsing time, and drying time between baths. The polyelectrolyte multilayers obtained with this method are infused with Krytox 100 to form SLIPS surfaces, which show excellent omniphobic, antifouling, self-cleaning, flexible, and optical properties. The result of this study not only simplifies the fabrication of SLIPS surfaces, but also provides great insight for making LBL films with specific morphologies.

A novel extrusion bioprinting system capable of individually and/or simultaneously depositing multiple different materials through a digitally tunable pneumatic system is developed by Y. S. Zhang, A. Khademhosseini, and co‐workers as described in article 1604630. The integration of a single‐printhead setup eliminates the need of physical nozzle switches, allowing for rapid and continuous fabrication of multicomponent structures.

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