Photodeformable Azobenzene‐Containing Liquid Crystal Polymers and Soft Actuators

Photodeformable liquid crystal polymers (LCPs) that adapt their shapes in response to light have aroused a dramatic growth of interest in the past decades, since light as a stimulus enables the remote control and diverse deformations of materials. This review focuses on the growing research on photodeformable LCPs, including their basic actuation mechanisms, the various deformation modes, the newly designed molecular structures, and the improvement of processing techniques. Special attention is devoted to the novel molecular structures of LCPs, which allow for easy processing and alignment. The soft actuators with various deformation modes such as bending, twisting, and rolling in response to light are also covered with the emphasis on their photo‐induced bionic functions. Potential applications in energy harvesting, self‐cleaning surfaces, sensors, and photo‐controlled microfluidics are further illustrated. The existing challenges and future directions are discussed at the end of this review.     

Light‐Mediated Manufacture and Manipulation of Actuators

Recent years have seen a considerable growth of research interests in developing novel technologies that permit designable manufacture and controllable manipulation of actuators. Among various fabrication and driving strategies, light has emerged as an enabler to reach this end, contributing to the development of actuators. Several accessible light‐mediated manufacturing technologies, such as ultraviolet (UV) lithography and direct laser writing (DLW), are summarized. A series of light‐driven strategies including optical trapping, photochemical actuation, and photothermal actuation for controllable manipulation of actuators is introduced. Current challenges and future perspectives of this field are discussed. To generalize, light holds great promise for the development of actuators.     

Soft Actuators for Small‐Scale Robotics

This review comprises a detailed survey of ongoing methodologies for soft actuators, highlighting approaches suitable for nanometer‐ to centimeter‐scale robotic applications. Soft robots present a special design challenge in that their actuation and sensing mechanisms are often highly integrated with the robot body and overall functionality. When less than a centimeter, they belong to an even more special subcategory of robots or devices, in that they often lack on‐board power, sensing, computation, and control. Soft, active materials are particularly well suited for this task, with a wide range of stimulants and a number of impressive examples, demonstrating large deformations, high motion complexities, and varied multifunctionality. Recent research includes both the development of new materials and composites, as well as novel implementations leveraging the unique properties of soft materials.     

Advanced Materials for Use in Soft Self‐Healing Devices

Devices integrated with self‐healing ability can benefit from long‐term use as well as enhanced reliability, maintenance and durability. This progress report reviews the developments in the field of self‐healing polymers/composites and wearable devices thereof. One part of the progress report presents and discusses several aspects of the self‐healing materials chemistry (from non‐covalent to reversible covalent‐based mechanisms), as well as the required main approaches used for functionalizing the composites to enhance their electrical conductivity, magnetic, dielectric, electroactive and/or photoactive properties. The second and complementary part of the progress report links the self‐healing materials with partially or fully self‐healing device technologies, including wearable sensors, supercapacitors, solar cells and fabrics. Some of the strong and weak points in the development of each self‐healing device are clearly highlighted and criticized, respectively. Several ideas regarding further improvement of soft self‐healing devices are proposed.     

Nanodroplet‐Containing Polymers for Efficient Low‐Power Light Upconversion

Sensitized triplet–triplet‐annihilation‐based photon upconversion (TTA‐UC) permits the conversion of light into radiation of higher energy and involves a sequence of photophysical processes between two dyes. In contrast to other upconversion schemes, TTA‐UC allows the frequency shifting of low‐intensity light, which makes it particularly suitable for solar‐energy harvesting technologies. High upconversion yields can be observed for low viscosity solutions of dyes; but, in solid materials, which are better suited for integration in devices, the process is usually less efficient. Here, it is shown that this problem can be solved by using transparent nanodroplet‐containing polymers that consist of a continuous polymer matrix and a dispersed liquid phase containing the upconverting dyes. These materials can be accessed by a simple one‐step procedure that involves the free‐radical polymerization of a microemulsion of hydrophilic monomers, a lipophilic solvent, the upconverting dyes, and a surfactant. Several glassy and rubbery materials are explored and a range of dyes that enable TTA‐UC in different spectral regions are utilized. The materials display upconversion efficiencies of up to ≈15%, approaching the performance of optimized oxygen‐free reference solutions. The data suggest that the matrix not only serves as mechanically coherent carrier for the upconverting liquid phase, but also provides good protection from atmospheric oxygen.     

Bio‐Hybrid Cell‐Based Actuators for Microsystems

As we move towards the miniaturization of devices to perform tasks at the nano and microscale, it has become increasingly important to develop new methods for actuation, sensing, and control. Over the past decade, bio‐hybrid methods have been investigated as a promising new approach to overcome the challenges of scaling down robotic and other functional devices. These methods integrate biological cells with artificial components and therefore, can take advantage of the intrinsic actuation and sensing functionalities of biological cells. Here, the recent advancements in bio‐hybrid actuation are reviewed, and the challenges associated with the design, fabrication, and control of bio‐hybrid microsystems are discussed. As a case study, focus is put on the development of bacteria‐driven microswimmers, which has been investigated as a targeted drug delivery carrier. Finally, a future outlook for the development of these systems is provided. The continued integration of biological and artificial components is envisioned to enable the performance of tasks at a smaller and smaller scale in the future, leading to the parallel and distributed operation of functional systems at the microscale.     

Self‐Assembled Biomimetic Capsules for Self‐Preservation

The inorganic semiconductor is an attractive material in sewage disposal and solar power generation. The main challenges associated with environment‐sensitive semiconductors are structural degradation and deactivation caused by the unfavorable environment. Here, inspired by the pomegranate, a self‐protection strategy based on the self‐assembly of silver chloride (AgCl) particles is reported. The distributed photosensitive AgCl particles can be encapsulated by themselves through mixing aqueous silver nitrate and protic ionic liquids (PILs). A probable assembling mechanism is proposed based on the electrostatic potential investigation of PILs cations. The AgCl particles inside the shell maintain their morphology and structure well after 6 months light‐treatment. Moreover, they exhibit excellent photocatalytic activity, same as newly prepared AgCl particles, for degradation of methyl orange (MO), neutral red (NR), bromocresol green (BG), rhodamine B (RhB), Congo red (CR), and crystal violet (CV).