Department of Chemistry, Northwestern University, Evanston, IL, 60208, USA.
Simpson Querrey Institute, Northwestern University, Chicago, IL, 60611, USA.
Nat Commun. 2018 Jun 19;9(1):2395. doi: 10.1038/s41467-018-04800-w.
Skeletal muscle provides inspiration on how to achieve reversible, macroscopic, anisotropic motion in soft materials. Here we report on the bottom-up design of macroscopic tubes that exhibit anisotropic actuation driven by a thermal stimulus. The tube is built from a hydrogel in which extremely long supramolecular nanofibers are aligned using weak shear forces, followed by radial growth of thermoresponsive polymers from their surfaces. The hierarchically ordered tube exhibits reversible anisotropic actuation with changes in temperature, with much greater contraction perpendicular to the direction of nanofiber alignment. We identify two critical factors for the anisotropic actuation, macroscopic alignment of the supramolecular scaffold and its covalent bonding to polymer chains. Using finite element analysis and molecular calculations, we conclude polymer chain confinement and mechanical reinforcement by rigid supramolecular nanofibers are responsible for the anisotropic actuation. The work reported suggests strategies to create soft active matter with molecularly encoded capacity to perform complex tasks.
骨骼肌为如何在软物质中实现可逆转的、宏观的、各向异性的运动提供了启示。在这里，我们报告了基于自下而上的设计，得到了宏观管状结构，该管状结构在热刺激下表现出各向异性的驱动。该管状结构是由水凝胶组成的，其中超长的超分子纳米纤维通过弱剪切力进行排列，然后从其表面径向生长出对温度响应的聚合物。具有层次有序结构的管状结构表现出可随温度变化的可逆各向异性驱动，垂直于纳米纤维排列方向的收缩程度更大。我们确定了各向异性驱动的两个关键因素，即超分子支架的宏观排列及其与聚合物链的共价键合。通过有限元分析和分子计算，我们得出结论，聚合物链的限制和由刚性超分子纳米纤维提供的机械增强是各向异性驱动的原因。这项工作提出了一些策略，可以创造出具有分子编码能力以执行复杂任务的软活性物质。
