Many creatures have the ability to traverse challenging environments by using their active muscles with anisotropic structures as the motors in a highly coordinated fashion. However, most artificial robots require multiple independently activated actuators to achieve similar purposes. Here we report a hydrogel-based, biomimetic soft robot capable of multimodal locomotion fueled and steered by light irradiation. A muscle-like poly(N-isopropylacrylamide) nanocomposite hydrogel is prepared by electrical orientation of nanosheets and subsequent gelation. Patterned anisotropic hydrogels are fabricated by multi-step electrical orientation and photolithographic polymerization, affording programmed deformations. Under light irradiation, the gold-nanoparticle-incorporated hydrogels undergo concurrent fast isochoric deformation and rapid increase in friction against a hydrophobic substrate. Versatile motion gaits including crawling, walking, and turning with controllable directions are realized in the soft robots by dynamic synergy of localized shape-changing and friction manipulation under spatiotemporal light stimuli. The principle and strategy should merit designing of continuum soft robots with biomimetic mechanisms.

Forming robust associative interactions has been an effective strategy for the design of tough hydrogels. However, the role of associative interactions in the dynamics of hydrogels still remains elusive. Here, we report a series of poly­(acrylamide-co-methacrylic acid) hydrogels with moderate water contents and excellent mechanical properties that are facilely synthesized by free-radical copolymerization. The mechanical properties of these hydrogels vary with the feeding molar fraction of acrylamide (f am). The gels with f am of 0.2–0.35 exhibit high toughness and good stability in water, which is related to the dense hydrogen bonds and relatively high segment rigidity of the matrix. Dynamic modulus spectra extended by time-temperature superposition and relaxation measurements indicate that the gels undergo glassy-to-rubbery transition with decreased frequency, and the robust hydrogen bonds, whose density is 1–3 times that of entanglements, retard chain disentanglement and contribute to the plateau modulus of the gels at low frequencies. The activation energy for the dissociation of the robust hydrogen bonds is ∼46 kJ mol–1. Furthermore, a decrease in water content results in the shift of dynamic modulus spectra to low frequencies and an increase in transition temperature due to the reduced segment relaxation. To further examine the structure of gel networks, the tensile behaviors of the gels are analyzed using a viscoelastic model. It is found that each partial chain includes 20–30 Kuhn segments, which are stretched after the fracture of intrachain hydrogen bonds to release the hidden length, dissipate energy, and thus toughen the gels. This understanding of the dynamics of the network at different timescales and the contribution of associative interactions to the mechanical properties should be informative for the design of other tough hydrogels.

Circularly polarized luminescence (CPL) is attractive in understanding the excited‐state chirality and developing advanced materials. Herein, we propose a chiral reticular self‐assembly strategy to unite achiral AIEgens, chirality donors, and metal ions to fabricate optically pure AIEgen metal–organic frameworks (MOFs) as efficient CPL materials. We have found that CPL activity of the single‐crystal AIEgen MOF was generated by the framework‐enabled strong emission from AIEgens and through‐space chirality transfer from chirality donors to achiral AIEgens via metal‐ion bridges. For the first time, a dual mechano‐switched blue and red‐shifted CPL activity was achieved via ultrasonication and grinding, which enabled the rotation or stacking change of AIEgen rotors with the intact homochiral framework. This work provided not only an insightful view of the aggregation induced emission (AIE) mechanism, but also an efficient and versatile strategy for the preparation of stimuli‐responsive CPL materials.

Zwitterionic hydrogels have attracted tremendous interest due to their densely charged network, ultralow fouling characteristics, and excellent biocompatibility. However, the unsatisfactory mechanical performance of the zwitterionic gels limits their practical applications. Here, we developed a new class of zwitterionic hydrogels from a structurally ameliorated sulfobetaine monomer, 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl)propane-1sulfonate (VBIPS). The incorporated benzene and imidazole greatly enhance the tensile toughness and fracture toughness of the gel, which are 40 and 60 times higher than those of the conventional zwitterionic hydrogel, respectively. An obvious crack blunting occurs during the crack extension. In situ microscopic observation reveals that the outstanding toughness originates from the formation of a two-phase structure at room temperature, with an obvious contrast of the association energy. The mechanical properties of the gel can be well-tuned by changing the pH, and self-healing is achieved with an acid treatment. The VBIPS gel also possesses excellent short-term antifouling properties and the attached bacteria in a longer timescale can be easily released via salt treatment. To expand the application potentials, a VBIPS ionogel is prepared by soaking the gel in ionic liquids, which is flexible, antifreezing, and can be used as a strain sensor. This work provides a molecular strategy to toughen zwitterionic hydrogels, which should broaden their applications in diverse fields.

No abstract

Tetraphenylethylene and its derivatives are a class of aggregation-induced emission (AIE) compounds that are most extensively and successfully studied. It has been found that the simplest TPE is easy to crystallize into homochiral M crystals or P crystals. However, no research on circularly polarized luminescence (CPL) of TPE solid is documented. In this paper, we report that TPE can grow into big and nonefflorescent single crystals in single helical conformation and has large birefringence that is comparative with commercially available products. The TPE single crystals can emit strong CPL with a very high g lum value up to 0.53. Moreover, the sense and magnitude of CPL signals can be willfully tuned by simple rotation of the single crystal due to anisotropy of the crystals. This simple and promising CPL photonic material integrates emission, chirality, and birefringence together in one single crystal without needing an additional chiral dopant or conjugate polymer that can produce linearly polarized light. After being ground into fine powder and pressed as KBr pellets, the obtained nanocrystals of TPE also emit strong CPL light. Exceptionally, by mixing other achiral luminescent dyes together with TPE powder in KBr pellets, induced CPL signals were obtained, which could give full-color CPL emission. Although there were no interactions between TPE and the dyes in the pellets, induced CPL signals were realized through radiative energy transfer, providing a very simple method for the tuning of CPL emission.

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Chiral covalent organic frameworks (COFs) with circularly polarized luminescence (CPL) are intriguing as advanced chiroptical materials but have not been reported to date.W ec onstructed chiroptical COF materials with CPL activity through the convenient Knoevenagel condensation of formyl-functionalized axially chiral linkers and C3-symmetric 1,3,5-benzenetriacetonitrile.R emarkably,t he as-prepared chiral COFs showed high absorption and luminescent dissymmetric factors up to 0.02 (g abs )a nd 0.04 (g lum ), respectively.I n contrast, the branched chiral polymers from the same starting monomers were CPL silent. Structural and spectral characterization revealed that the reticular frame was indispensable for CPL generation via confined chirality transfer.M oreover, reticular stacking boosted the CPL performance significantly due to the interlayer restriction of frame.T his work demonstrates the first example of aC PL-active COF and provides insight into CPL generation through covalent reticular chemistry,w hich will play ac onstructive role in the future design of high-performance CPL materials.