Mimicking the locomotive abilities of living organisms on the microscale, where the downsizing of rigid parts and circuitry presents inherent problems, is a complex feat. In nature, many soft-bodied organisms (inchworm, leech) have evolved simple, yet efficient locomotion strategies in which reciprocal actuation cycles synchronize with spatiotemporal modulation of friction between their bodies and environment. We developed microscopic (∼100 μm) hydrogel crawlers that move in aqueous environment through spatiotemporal modulation of the friction between their bodies and the substrate. Thermo-responsive poly-n-isopropyl acrylamide hydrogels loaded with gold nanoparticles shrink locally and reversibly when heated photothermally with laser light. The out-of-equilibrium collapse and reswelling of the hydrogel is responsible for asymmetric changes in the friction between the actuating section of the crawler and the substrate. This friction hysteresis, together with off-centered irradiation, results in directional motion of the crawler. We developed a model that predicts the order of magnitude of the crawler motion (within 50%) and agrees with the observed experimental trends. Crawler trajectories can be controlled enabling applications of the crawler as micromanipulator that can push small cargo along a surface.

中文翻译：

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光响应水凝胶微爬行器利用摩擦滞后通过相互驱动进行爬行

在微观尺度上模仿生物体的运动能力是一项复杂的壮举，其中刚性部件和电路的缩小存在固有问题。在自然界中，许多软体生物（尺蠖、水蛭）已经进化出简单而有效的运动策略，其中相互驱动周期与它们身体和环境之间摩擦的时空调制同步。我们开发了微观（~100 μm）水凝胶爬行器，它们通过时空调制它们的身体和基板之间的摩擦力在水环境中移动。负载有金纳米粒子的热响应性聚正异丙基丙烯酰胺水凝胶在用激光光热加热时会局部和可逆地收缩。水凝胶的不平衡塌陷和再膨胀是导致履带驱动部分与基板之间摩擦力不对称变化的原因。这种摩擦滞后与偏心照射一起导致履带的定向运动。我们开发了一个模型，可以预测履带运动的数量级（在 50% 以内），并且与观察到的实验趋势一致。可以控制履带轨迹，从而使履带能够作为微操纵器应用，沿着表面推动小型货物。我们开发了一个模型，可以预测履带运动的数量级（在 50% 以内），并且与观察到的实验趋势一致。可以控制履带轨迹，从而使履带能够作为微操纵器应用，沿着表面推动小型货物。我们开发了一个模型，可以预测履带运动的数量级（在 50% 以内），并且与观察到的实验趋势一致。可以控制履带轨迹，从而使履带能够作为微操纵器应用，沿着表面推动小型货物。