Near‐Infrared Light‐Driven Shape‐Morphing of Programmable Anisotropic Hydrogels Enabled by MXene Nanosheets

DNA Cryogels with Anisotropic Mechanical and Responsive Properties for Specific Cell Capture and Release

Due to their programmable stimuli-responsiveness, excellent biocompatibility, and water-rich and soft structures similar to biological tissues, smart DNA hydrogels hold great promise for biosensing and biomedical applications. However, most DNA hydrogels developed to date are composed of randomly oriented and isotropic polymer networks, and the resulting slow response to biotargets and lack of anisotropic properties similar to those of biological tissues have limited their extensive applications. Herein, anisotropic DNA hydrogels consisting of unidirectional void channels internally oriented up to macroscopic length scales were constructed by a directional cryopolymerization method, as exemplified by a DNA-incorporated covalently cross-linked DNA cryogel and a DNA duplex structure noncovalently cross-linked DNA cryogel. Results showed that the formation of unidirectional channels significantly improved the responsiveness of the gel matrix to biomacromolecular substances and further endowed the DNA cryogels with anisotropic properties, including anisotropic mechanical properties, anisotropic swelling/shrinking behaviors, and anisotropic responsiveness to specific biotargets. Moreover, the abundant oriented and long macroporous channels in the gel matrix facilitated the migration of cells, and through the introduction of aptamer structures and thermosensitive polymers, an anisotropic DNA cryogel-based platform was further constructed to achieve the highly efficient capture and release of specific cells. These anisotropic DNA hydrogels may provide new opportunities for the development of anisotropic separation and biosensing systems.

Mechanical Training Enabled Reinforcement of Polyrotaxane-Containing Hydrogel

Many strategies have been developed for constructing anisotropic hydrogels, however, it remains a challenge to fabricate hydrogels with anisotropic nanocrystalline domains from intrinsically soft networks. Here, we report a naphthotube-based polyrotaxane-containing hydrogel that can be reinforced via mechanical training. During the training process, the hydrogel can adopt reorientation of polymer chains to form anisotropic structures driven by external uniaxial force. Due to the multiple hydrogen bonding sites and movable feature of naphthotube, the sliding of naphthotube on PEG chains simultaneously inducing the zipping of adjacent polymer chains to form densely anisotropic nanocrystalline domains through hydrogen bonded networks. Thus, the trained hydrogel exhibits an enhanced tension stress of ≈110 kPa, which realize a remarkable enhancement of ≈10 times compare to initial state. This study provides a new tactic for improving the mechanical performance of soft materials.

Magneto-Orientation of Magnetic Double Stacks for Patterned Anisotropic Hydrogels with Multiple Responses and Modulable Motions

Reported here is a multi-response anisotropic poly(N-isopropylacrylamide) hydrogel developed by using a rotating magnetic field to align magnetic double stacks (MDSs) that are fixed by polymerization. The magneto-orientation of MDSs originates from the unique structure with γ-Fe₂ O₃ nanoparticles sandwiched by two silicate nanosheets. The resultant gels not only exhibit anisotropic optical and mechanical properties but also show anisotropic responses to temperature and light. Gels with complex ordered structures of MDSs are further devised by multi-step magnetic orientation and photolithographic polymerization. These gels show varied birefringence patterns with potentials as information materials, and can deform into specific configurations upon stimulations. Multi-gait motions are further realized in the patterned gel through dynamic deformation under spatiotemporal light and friction regulation by imposed magnetic force. The magneto-orientation assisted fabrication of hydrogels with anisotropic structures and additional functions should bring opportunities for gel materials in biomedical devices, soft actuators/robots, etc.

Mechanochromic, Shape-Programmable and Self-Healable Cholesteric Liquid Crystal Elastomers Enabled by Dynamic Covalent Boronic Ester Bonds

Endowing a cholesteric liquid crystal elastomer (CLCE) exhibiting helicoidal nanostructure with dynamically tailorable functionalities is of paramount significance for its emerging applications in diverse fields such as adaptive optics and soft robotics. Here, a mechanochromic, shape-programmable and self-healable CLCE is judiciously designed and synthesized through integrating dynamic covalent boronic ester bonds into the main-chain CLCE polymer network. The circularly polarized reflection of CLCEs can be reversibly and dynamically tuned across the entire visible spectrum by mechanical stretching. Thanks to the introduction of dynamic boronic ester bonds, the CLCEs were found to show robust reprogrammable and self-healing capabilities. The research disclosed herein can provide new insights into the development of 4D (color and 3D shape) programmable photonic actuators towards bioinspired camouflage, adaptive optical systems, and next-generation intelligent machines.

Remotely Controlling Drug Release by Light-Responsive Cholesteric Liquid Crystal Microcapsules Triggered by Molecular Motors

Stimuli-responsive smart nanocarriers are an emerging class of materials applicable in fields including drug delivery and tissue engineering. Instead of constructing responsive polymer shells to control the release and delivery of drugs, in this work, we put forward a novel strategy to endow the internal drugs with light responsivity. The microcapsule consisted of molecular motor (MM)-doped cholesteric liquid crystals (CLCs) and drugs. The drug in gelatin-gum arabic microcapsules can protect the carried drugs for a long time with a low release speed totally resulting from drug diffusion. Under UV light, the MM isomerizes and the chirality changes, inducing the alteration of the superstructure of the CLCs. In this process, the cooperative molecular disturbance accelerates the diffusion of the drugs from the microcapsule core to the outside. As a result, thanks to the cooperative effect of liquid crystalline mesogens, molecular-scale geometric changes of motors could be amplified to the microscale disturbance of the self-organized superstructure of the CLCs, resulting in the acceleration of the drug release. This method is hoped to provide opportunities in the design and fabrication of novel functional drug delivery systems.

Light-Driven Self-Oscillating Actuators with Phototactic Locomotion Based on Black Phosphorus Heterostructure

Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.

Healable and Rearrangeable Networks of Liquid Crystal Elastomers Enabled by Diselenide Bonds

Based on liquid crystal elastomer (LCE) materials, hierarchically structured soft actuators can meet some requirements for "human-friendly" working mode and execute complex tasks with intelligent adaptation to environmental changes. However, few researchers have paid much attention to the preparation methods of multicomponent/hierarchical LCE actuators. In this communication, we demonstrate the successful integration of an exchangeable diselenide chain extender for the preparation of dynamic LCEs, which could be reprogrammed on heating or under visible light illumination. Moreover, the rearrangeable polydiselenide networks could be applied to develop the self-welding technology toward fabricating hierarchically structured LCE actuators with sophisticated deformability without using any auxiliary reagent (adhesive, tape, catalysts or initiator) during the assembling process.