Encoding Smart Microjoints for Microcrawlers with Enhanced Locomotion

Abstract

Usually, it is indispensable for traditional functional robots to use flexible joints that integrate sophisticated machinery and control systems to achieve precise operability and efficient mobility. At the microscale, however, the conventional design of functional joints is generally not suitable due to the limitation of the manufacturing process on such a tiny size. Herein, a strategy for the design of smart microjoints (SMJs) that undergo controllable active deformation by triggering a size‐dependent layer‐by‐layer sequential swelling effect on SMJs in response to external stimuli is developed. The optimal encoding of SMJs that enables microcrawlers to achieve superior crawling speed (0.15 body length s−1) and efficiency (1.1 body length per step), as well as controllable locomotion, is demonstrated, e.g., migration along/against the stimuli source or along a preplanned path. A path toward constructing soft actuators/robots at the microscale with high adaptability and controllability for broad engineering applications is offered.

Intelligent Shape-Morphing Micromachines

“…Honschoten et al [ 51 ] fabricated a microstructure with a silicon nitride layer and then created hinges by photolithography and plasma etching of the layer to a thinner thickness as the crease for folding. Chen et al [ 57 ] and Jin et al [ 54 ] embedded narrow bilayer structures into micromachines for obviously fixed-point folding ( Figure 2(g) ). In general, the folding direction is predesigned, rather than random swings like chaining.…”

“…Though it is a random and unpredictable process in a static fluid, the diffusion path could be artificially controlled when the velocity of the fluid is greater than the diffusion speed. Chen et al [ 57 ] proposed a shape-morphing realization strategy to trigger a series of microcrawlers walking along a predesigned diffusion path ( Figure 3(b) ). Through controlling of injecting directions and rates of the alkaline solution into the acidic solution, the trajectories of neutralization reaction could be manipulated.…”

“…When different regions of intelligent micromachines are triggered by different deformation degrees or stimuli, the whole micromachines realize asymmetric-response shape morphing [ 43 , 47 – 50 , 54 , 57 , 69 ]. For example, Gao et al [ 44 ] reported a synthetic hybrid wire-shaped motor at the microscale.…”

“…Asymmetric triggering time is an effective internal asymmetric factor for the realization of shape morphing. Chen et al [ 57 ] found a sequential deformation effect of pH-response bilayer beams at the microscale. The layer with dense crosslinking density was triggered ahead of the loose one in response to the change in the ambient solution from acidic to alkaline and induced sequential swelling between two layers of the microbeam.…”

“…Here, we list eight types of applications of intelligent micromachines which are divided into motion- and target-based micromachines, as shown in Figure 4 . The motion-based micromachines include microswimmers for swimming in the liquid [ 23 , 30 , 41 – 44 ], microcrawlers for substrate locomotion [ 57 , 64 ], microjumpers for jumping [ 64 , 86 ], and micromotors for marching [ 52 , 53 , 58 , 87 ], while the target-based micromachines include microvalves for valve control of microchannels [ 35 , 36 ], microstents for extending vessels [ 54 , 88 ], microgrippers for drugs catching [ 26 , 47 , 49 , 56 , 66 ], and microcarriers for drug carrying and delivery [ 29 , 89 , 90 ]. Each application is summarized and marked with its common strategies according to the shape-morphing dimension, shape-morphing modes, and realization methods discussed above, together with their advantages and limitations (see Table 1 for details).…”