Cephalopods use chromatophores distributed on their soft skin to change skin color and its pattern. Each chromatophore consists of a central sac containing pigment granules and radial muscles surrounding the sac. The contraction of the radial muscle causes the central sac to expand in area, making the color of the pigment more visible. With the chromatophores actuating individually, cephalopods can create extremely complex skin color patterns, which they utilize for exquisite functions including camouflage and communication. Inspired by this mechanism, we present an artificial chromatophore that can modulate its color pattern in response to light. Multimaterial projection microstereolithography is used to integrate three functional components including a photoactive hydrogel composite with polydopamine nanoparticles (PDA-NPs), acrylic acid hydrogel, and poly(ethylene glycol) diacrylate. In order to generate light-driven actuation of the artificial chromatophore, the photothermal effect of the PDA-NPs, light-responsive deformation of the photoactive hydrogel composite, and the produced mechanical stresses are studied. Mechanical properties and interfacial bonding strengths between different materials are also investigated to ensure structural integrity during actuation. We demonstrate pattern modulation of the light-responsive artificial chromatophores (LACs) with the projection of different light patterns. The LAC may suggest a new concept for various engineering applications such as the camouflage interface, biophotonic device, and flexible display. 

3D cell cultures are rapidly emerging as a promising tool to model various human physiologies and pathologies by closely recapitulating key characteristics and functions of in vivo microenvironment. While high-throughput 3D culture is readily available using multi-well plates, assessing the internal microstructure of 3D cell cultures still remains extremely slow because of the manual, laborious, and time-consuming histological procedures. Here, a 4D-printed transformable tube array (TTA) using a shape-memory polymer that enables massively parallel histological analysis of 3D cultures is presented. The interconnected TTA can be programmed to be expanded by 3.6 times of its printed dimension to match the size of a multi-well plate, with the ability to restore its original dimension for transferring all cultures to a histology cassette in order. Being compatible with microtome sectioning, the TTA allows for parallel histology processing for the entire samples cultured in a multi-well plate. The test result with human neural progenitor cell spheroids suggests a remarkable reduction in histology processing time by an order of magnitude. High-throughput analysis of 3D cultures enabled by this TTA has great potential to further accelerate innovations in various 3D culture applications such as high-throughput/content screening, drug discovery, disease modeling, and personalized medicine. 

 Microneedle (MN), a miniaturized needle with a length-scale of hundreds of micrometers, has received a great deal of attention because of its minimally invasive, pain-free, and easy-to-use nature. However, a major challenge for controlled long-term drug delivery or biosensing using MN is its low tissue adhesion. Although microscopic structures with high tissue adhesion are found from living creatures in nature (e.g., microhooks of parasites, barbed stingers of honeybees, quills of porcupines), creating MNs with such complex microscopic features is still challenging with traditional fabrication methods. Here, a MN with bioinspired backward-facing curved barbs for enhanced tissue adhesion, manufactured by a digital light processing 3D printing technique, is presented. Backward-facing barbs on a MN are created by desolvation-induced deformation utilizing cross-linking density gradient in a photocurable polymer. Barb thickness and bending curvature are controlled by printing parameters and material composition. It is demonstrated that tissue adhesion of a backward-facing barbed MN is 18 times stronger than that of barbless MN. Also demonstrated is sustained drug release with barbed MNs in tissue. Improved tissue adhesion of the bioinspired MN allows for more stable and robust performance for drug delivery, biofluid collection, and biosensing.

 The exotic properties of mechanical metamaterials emerge from the topology of micro-structural elements. Once manufactured, however, the metamaterials have fixed properties without the ability to adapt and adjust. Here, we present geometrically reconfigurable, functionally deployable, and mechanically tunable lightweight metamaterials created through four-dimensional (4D) printing. Using digital micro 3D printing with a shape memory polymer, dramatic and reversible changes in the stiffness, geometry, and functions of the metamaterials are achieved.

 Electroactive hydrogels (EAH) that exhibit large deformation in response to an electric field have received great attention as a potential actuating material for soft robots and artificial muscle. However, their application has been limited due to the use of traditional two-dimensional (2D) fabrication methods. Here we present soft robotic manipulation and locomotion with 3D printed EAH microstructures. Through 3D design and precise dimensional control enabled by a digital light processing (DLP) based micro 3D printing technique, complex 3D actuations of EAH are achieved. We demonstrate soft robotic actuations including gripping and transporting an object and a bidirectional locomotion.