Multi-stimuli-responsive programmable biomimetic actuator

Abstract

Untethered small actuators have various applications in multiple fields. However, existing small-scale actuators are very limited in their intractability with their surroundings, respond to only a single type of stimulus and are unable to achieve programmable structural changes under different stimuli. Here, we present a multiresponsive patternable actuator that can respond to humidity, temperature and light, via programmable structural changes. This capability is uniquely achieved by a fast and facile method that was used to fabricate a smart actuator with precise patterning on a graphene oxide film by hydrogel microstamping. The programmable actuator can mimic the claw of a hawk to grab a block, crawl like an inchworm, and twine around and grab the rachis of a flower based on their geometry. Similar to the large- and small-scale robots that are used to study locomotion mechanics, these small-scale actuators can be employed to study movement and biological and living organisms.

Fig. 1

Fabrication and programmable structure changes of actuator. a Schematic diagram of precise PPy patterning on a GO film for the fabrication of a programmed GO/PPy actuator; b optical image of precise PPy patterning on a GO film (Scale bar: 100 μm); c working mechanism of GO/PPy bilayer actuator and the structural changes of actuators with regular triangle, square, regular pentagon, regular hexagon, and H-, U-, S-, and T-shape patterns under the stimuli of humidity and IR light; d schematic diagram of a programmable GO/PPy actuator

Fig. 2

Structural characterization of GO/PPy actuator. SEM image of a the GO film side and b the PPy side; cross-sectional SEM image of GO/PPy actuators fabricated on the basis of GO films with different thicknesses of c 12.8 μm, d 25.2 μm and e 37.1 μm; f XPS spectra of GO and GO/PPy; g XRD pattern of GO and GO/PPy; h Raman spectra of GO and GO/PPy; i FT-IR spectra of pure GO and GO/PPy

Fig. 3

Actuating performance of GO/PPy actuator. a Actuating performance of GO/PPy actuators under the stimulus of humidity, (GO/PPy (a), GO/PPy (b) and GO/PPy (c) represent GO/PPy actuators with different GO thicknesses of 12.8, 25.2 and 37.1 μm, respectively) (the insets are photographs of the bending GO/PPy ribbon under different RH values); b Actuating performance of GO/PPy actuators under the stimulus of humidity, (GO/PPy (d), GO/PPy (e) and GO/PPy (b) represent GO/PPy actuators with increasing PPy thicknesses and same GO thickness of 25.2 μm; c switching from the bent to the straight state of GO/PPy (b) by changing the corresponding RH from 50 to 68%, and vice versa; d cyclic stability of the curvature of a GO/PPy actuator over 100 cycles (50–68% RH); e durable behavior of GO/PPy (b) after exposure to 57% or 67% RH for 600 s; f actuating performance of GO/PPy (b) under the stimulus of temperature (the insets are photographs of the bending GO/PPy ribbon at temperatures of 25, 50 and 100 °C); g actuating performance of GO/PPy (b) under the stimulus of IR light (the insets are photographs of the bending GO/PPy (b) at different times); h the bending force of GO/PPy (b) actuator recorded during the process of turning on/off the humidifier; i the contractile force of GO/PPy (b) actuator recorded during the process of turning on/off IR light with power densities of 0.0423, 0.0831 and 0.126 W cm⁻² (from left to right)

Fig. 4

Biomimetic gripper with cross and helical structure. a Schematic illustration of a smart GO/PPy gripper with a cross structure inspired by the claw of a hawk (middle image). It exhibits a straight state at room humidity (≈50% RH, left images) and a bent state at high humidity (≈80% RH, right images). b The process of a foam being picked up and released by a smart GO/PPy gripper; c schematic illustration of a smart GO/PPy tendril-inspired by a tendril climber plant (right images). The tendril curves at room humidity (≈50% RH, left images) and curls to a helical structure under high humidity (≈80% RH, middle images); d a flower can be removed from a homemade vase by the helical GO/PPy gripper

Fig. 5

Biomimetic soft walking robot. a the movement process of the inchworm; b the schematic diagram of soft walking robot and its movement; c the movement process of the soft walking robot under the interval stimulus of IR light