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.

4D bioprinting is promising to build cell‐laden constructs (bioconstructs) with complex geometries and functions for tissue/organ regeneration applications. The development of hydrogel‐based 4D bioinks, especially those allowing living cell printing, with easy preparation, defined composition, and controlled physical properties is critically important for 4D bioprinting. Here, a single‐component jammed micro‐flake hydrogel (MFH) system with heterogeneous size distribution, which differs from the conventional granular microgel, has been developed as a new cell‐laden bioink for 4D bioprinting. This jammed cytocompatible MFH features scalable production and straightforward composition with shear‐thinning, shear‐yielding, and rapid self‐healing properties. As such, it can be smoothly printed into stable 3D bioconstructs, which can be further cross‐linked to form a gradient in cross‐linking density when a photoinitiator and a UV absorber are incorporated. After being subject to shape morphing, a variety of complex bioconstructs with well‐defined configurations and high cell viability are obtained. Based on this system, 4D cartilage‐like tissue formation is demonstrated as a proof‐of‐concept. The establishment of this versatile new 4D bioink system may open up a number of applications in tissue engineering.

Four [12]aneN3 modified tetraphenylethene (TPE) compounds with different numbers of polyamine units and structure configurations, namely 1, 2, 3, and 4, were designed and synthesized. All compounds showed strong aggregation-induced emission (AIE) features. Compounds 2 and 4 showed significant emission enhancement after the addition of ssDNAs and dsDNAs of different lengths as well as calf thymus DNA (ctDNA). Compounds 1 and 3 showed very poor fluorescent responses toward DNAs. Gel electrophoresis demonstrated the abilities of 1-4 to condense DNA effectively. Complete retardation of plasmid DNA can be achieved at a concentration of 25 μM (1), 8 μM (for 2 and 3) and 4 μM (4). Experiments including fluorescent contrastive titrations, scanning electron microscopy, dynamic laser scattering, EB displacement, and gel electrophoresis demonstrated that the four compounds were able to integrate with DNA through electrostatic interactions and supramolecular stacking. A vicinal configuration around TPE (2) and more triazole-[12]aneN3 recognition sites (4) evidently enhanced the sensing capability toward oligonucleotides, and the TPE unit played an important role in the plasmid DNA condensation process because of its strong binding. With the advantages of low cytotoxicity, effective DNA sensing, and DNA condensing properties, compound 4 was successfully applied as a nonviral DNA vector and fluorescent tracer for label-free gene delivery, which is the first example of a nonviral gene vector with AIE activity.

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.