Liquid crystal elastomers (LCEs), which are composed of liquid crystal mesogens and polymer networks, exhibit excellent actuation performance and tailorable energy dissipation behavior. They have shown great potential in practical applications in artificial muscles, soft robotics, and wearable devices. However, it is challenging to fabricate LCE samples in arbitrary three-dimensional (3D) shapes and desired alignment patterns with traditional manufacturing methods. Recently, 3D printing techniques have been introduced in combination with alignment methods of LCEs to meet this challenge. In this Review, we highlight recent advances in the 3D printing techniques of LCEs. Two kinds of printing techniques, materials extrusion and vat photopolymerization, are discussed in detail. We compare the differences and key parameters in the printing techniques, such as director fields, resolutions, and printing speeds. The applications of the printed LCE structures in soft robots, reconfigurable surfaces, and haptic devices are also introduced.

Mechanochromic hydrogels, which can switch their color in response to the applied external force, have shown great potential in stress visualization and damage indication. However, the kinds of colors in the reported mechanochromic hydrogels are limited. It is challenging to develop mechanochromic hydrogels with new kinds of color changes. Herein, a kind of mechanochromic double network (DN) hydrogel is reported based on the hybrid phenol-rhodamine mechanophore. The hydrogels turn into orange color with an emission wavelength of around 566/574 nm in response to tensile and compressive stress. The DN hydrogels show great reversibility. The color of DN hydrogels vanishes slowly after releasing the stress. The stress sensitivity can be tailored by the crosslinking density and the mechanophore concentration of the first network. In addition, the influence of the pH on the mechanochromic properties of DN hydrogels is also studied. This study provides an insightful study in tuning the stress sensitivity in the mechanochromic hydrogel, which will be beneficial for the development of mechanochromic materials.

Cephalopods can change their color and patterns by activating the skin chromatophores for camouflage. However, in the man-made soft material systems, it is greatly challenging to fabricate the color-change structure in the desired patterns and shapes. Herein, we employ a multi-material microgel direct ink writing (DIW) printing method to make mechanochromic double network hydrogels in arbitrary shapes. We prepare the microparticles by grinding the freeze-dried polyelectrolyte hydrogel and immobilize the microparticles in the precursor solution to produce the printing ink. The polyelectrolyte microgels contain mechanophores as the cross-linkers. We adjust the rheological and printing properties of the microgel ink by tailoring the grinding time of freeze-dried hydrogels and microgel concentration. The multi-material DIW 3D printing technique is utilized to fabricate various 3D hydrogel structures which could change into a colorful pattern in response to applied force. The microgel printing strategy shows great potential in the fabrication of the mechanochromic device with arbitrary patterns and shapes.

Herein, we report a novel aminobenzopyranoxanthene (ABPX) mechanophore featuring double spiro rings. ABPXs were introduced into a series of poly(methyl acrylate)s (PMA) with different molecular weights to experience gradient forces...

The design of new aggregation-induced emission luminogens (AIEgens) has aroused continuous attention. The relationship between structure and performance plays an important role in guiding such efforts. In this contribution, two R−D−A-and R−D−π−A-type AIEgens were facilely designed and synthesized, that is, DPE-PTZ-CN and DPE-PTZ-PCN, with diphenylethylene as the twisted rotor structure (R), phenothiazine as electron-donor (D), and the (aryl) cyano group as electron-acceptor (A) fragments. Both luminophores were endowed with typical AIE properties, while their α AIE (PL intensity ratio of AIEgen in a mixed solution with water fraction (f w ) = 90 vol % to that with f w = 0) were quite different. The α AIE for DPE-PTZ-CN was as high as 41, but it was only 3 for DPE-PTZ-PCN, in which the π-bridge (aryl linker) was introduced between its D and A groups. In addition, the push−pull electronic effect endowed both molecules with the feature of intramolecular charge transfer (ICT). The solvatochromism effect observed in solutions with different polarities confirmed the existence of the ICT process. The theoretical calculation and single crystal structure analysis revealed that the electronic structure and molecular conformation characteristics had a decisive influence on the differences in photophysical behaviors.