using a delicate draw-spinning process such as that of spider silk is challenging. Crosslinking is one of the indispensable structural characteristics contributing to the strength and toughness of fibers. This is because the molecular chains are locked in the crosslinking network, [12] however, making it nonspinnable.Efforts have been made to spin a fiber from a linear polymer or a soluble precursor followed by an additional crosslinking step. [6,7,13] Moreover, novel spinning methods, such as wet spinning, [14,15] dry spinning, [16,17] micro fluidic spinning, [18][19][20] electro-spinning, [21,22] templating, [23] and dynamic crosslinked spinning, [24] have been developed. However, this increases the complexity of the spinning process, and controlling the hierarchical structure of the fiber becomes difficult. Consequently, so far the combination of strength and toughness of the artificial fibers still have a big gap to reach those of the spider dragline silk.The β-sheets in spidroin serve as crosslinking points, and the crosslinking network is localized inside this nanometersized globular protein. Therefore, spidroin is soluble and can be directly draw-spun to produce a hierarchical fiber via selfassembly (Figure 1a). Inspired by the spidroin structure and the spinning process, herein we prepared a soluble nanogel with an internal crosslinked network, which can be drawn-spun to form hierarchical fibers with nanoassemblies (Figure 1b). Theoretical modeling provided understanding of the fiber's spinning capacity as a function of the nanogel size. The introduction of Spider dragline silk is draw-spun from soluble, β-sheet-crosslinked spidroin in aqueous solution. This spider silk has an excellent combination of strength and toughness, which originates from the hierarchical structure containing β-sheet crosslinking points, spiral nanoassemblies, a rigid sheath, and a soft core. Inspired by the spidroin structure and spider spinning process, a soluble and crosslinked nanogel is prepared and crosslinked fibers are drew spun with spider-silk-like hierarchical structures containing cross-links, aligned nanoassemblies, and sheath-core structures. Introducing nucleation seeds in the nanogel solution, and applying prestretch and a spiral architecture in the nanogel fiber, further tunes the alignment and assembly of the polymer chains, and enhances the breaking strength (1.27 GPa) and toughness (383 MJ m −3 ) to approach those of the best dragline silk. Theoretical modeling provides understanding for the dependence of the fiber's spinning capacity on the nanogel size. This work provides a new strategy for the direct spinning of tough fiber materials.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202201843.
A microfluidic manipulation system that can sense a liquid and control its flow is highly desirable. However, conventional sensors and motors have difficulty fitting the limited space in microfluidic devices; moreover, fast sensing and actuation are required because of the fast liquid flow in the hollow fibre. In this study, fast torsional and tensile actuators were developed using hollow fibres employing spiral nonlinear stress, which can sense the fluid temperature and sort the fluid into the desired vessels. The fluid-driven actuation exhibited a highly increased response speed (27 times as fast as that of air-driven actuation) and increased power density (90 times that of an air-driven solid fibre actuator). A 0.5 K fluid temperature fluctuation produced a 20° rotation of the hollow fibre. These high performances originated from increments in both heat transfer and the average bias angle, which was understood through theoretical analysis. This work provides a new design strategy for intelligent microfluidics and inspiration for soft robots and smart devices for biological, optical, or magnetic applications.
Continuous mechanical work output can be generated by using combustion engines and electric motors, as well as actuators, through on/off control via external stimuli. Solar energy has been used to generate electricity and heat in human daily life; however, the direct conversion of solar energy to continuous mechanical work has not been realized. In this work, a solar engine is developed using an oscillating actuator, which is realized through an alternating volume decrease of each side of a polypropylene/carbon black polymer film induced by photothermal-derived solvent evaporation. The anisotropic solvent evaporation and fast gradient diffusion in the polymer film sustains oscillating bending actuation under the illumination of divergent light. This light-driven oscillator shows excellent oscillation performance, excellent loading capability, and high energy conversion efficiency, and it can never stop with solvent supply. The oscillator can cyclically lift up a load and output work, exhibiting a maximum specific work of 30.9 × 10−5 J g−1 and a maximum specific power of 15.4 × 10−5 W g−1 under infrared light. This work can inspire the development of autonomous devices and provide a design strategy for solar engines.
This review summarizes the recent progress in twisted-fiber artificial muscles with different methods for preserving the torque and the inserted twist, and explores the relevant applications.
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