Formation of graded biomaterials to render shape-morphing scaffolds for 4D biofabrication holds great promise in fabrication of complex structures and the recapitulation of critical dynamics for tissue/organ regeneration. Here we describe a facile generation of an adjustable and robust gradient using a single- or multi-material one-step fabrication strategy for 4D biofabrication. By simply photocrosslinking a mixed solution of a photocrosslinkable polymer macromer, photoinitiator (PI), UV absorber and live cells, a cell-laden gradient hydrogel with pre-programmable deformation can be generated. Gradient formation was demonstrated in various polymers including poly(ethylene glycol) (PEG), alginate, and gelatin derivatives using various UV absorbers that present overlap in UV spectrum with that of the PI UV absorbance spectrum. Moreover, this simple and effective method was used as a universal platform to integrate with other hydrogel-engineering techniques such as photomask-aided microfabrication, photo-patterning, ion-transfer printing, and 3D bioprinting to fabricate more advanced cell-laden scaffold structures. Lastly, proof-of-concept 4D tissue engineering was demonstrated in a study of 4D bone-like tissue formation. The strategy's simplicity along with its versatility paves a new way in solving the hurdle of achieving temporal shape changes in cell-laden single-component hydrogel scaffolds and may expedite the development of 4D biofabricated constructs for biological applications.

Two α-cyanostilbene derivatives exhibiting bright emission in both well-dissolved solutions (Φ > 49%) and the solid state (Φ > 95%) have been synthesized as novel DSEgens for high-contrast mechanofluorochromism (>50 nm) and live cell imaging.

Shape‐morphing hydrogels bear promising prospects as soft actuators and for robotics. However, they are mostly restricted to applications in the abiotic domain due to the harsh physicochemical conditions typically necessary to induce shape morphing. Here, multilayer hydrogel actuator systems are developed using biocompatible and photocrosslinkable oxidized, methacrylated alginate and methacrylated gelatin that permit encapsulation and maintenance of living cells within the hydrogel actuators and implement programmed and controlled actuations with multiple shape changes. The hydrogel actuators encapsulating cells enable defined self‐folding and/or user‐regulated, on‐demand‐folding into specific 3D architectures under physiological conditions, with the capability to partially bioemulate complex developmental processes such as branching morphogenesis. The hydrogel actuator systems can be utilized as novel platforms for investigating the effect of programmed multiple‐step and reversible shape morphing on cellular behaviors in 3D extracellular matrix and the role of recapitulating developmental and healing morphogenic processes on promoting new complex tissue formation.

Leveraging dual-state emitters (DSEgens) to achieve intense emission in both dilute solutions and the solid state is rapidly emerging as a trending research spot in the field of luminescent materials as these materials have found wide applications in dual states. Despite the advance in materials and applications, it is still challenging to obtain a DSEgen through a rational molecule design. Herein, we propose a molecular engineering strategy to afford two arylimidazole emitters, NIFBCZ and NIBBCZ, as DSEgens with highly twisting conformation by fusing multiple rigid, planar units into a molecule. NIFBCZ and NIBBCZ have high emission quantum yields (QYs) of 52.3% and 62.7% in THF solution and 42.5% and 62.4% in the solid state. Single crystal X-ray diffraction study and theoretical calculation reveal that the highly twisting conformation, the presence of multi-intramolecular weak interactions, and effective intramolecular charge transfer (ICT) play key roles in the dual-state emission. With the two DSEgens, clear mechanochromism, specific recognition of picric acid (PA) over various nitroaromatic compounds (NACs), and trace water detection in organic solvents were demonstrated. The detection limits are 97 nM (PA) and 0.0010% (water) for NIFBCZ and 180 nM (PA) and 0.0027% (water) for NIBBCZ. Of particular note, the higher QY of NIFBCZ in comparison with that of NIBBCZ could stem from its enhanced local rigidity and planarity by the coupling of the two phenyl pendants in the arylimidazole core, suggesting the active role of local rigidification in improving the photophysical properties. The new molecular engineering strategy in this study provides a new paradigm for the design of DSEgens.