Light-driven lattice soft microrobot with multimodal locomotion

Abstract

Untethered microrobots hold significant promise in fields such as bionics, biomedicine, and micromechanics. However, replicating the diverse movements of natural microorganisms in artificial microrobots presents a considerable challenge. This paper introduces a laser-based approach that utilizes lattice metamaterials to enhance the deformability of hydrogel-based microrobots, resulting in untethered light-driven lattice soft microrobots (LSMR). Constructed from poly(N-isopropylacrylamide)-single-walled carbon nanotubes (PNIPAM-SWNT) hydrogels and a truncated octahedron lattice structure, the LSMR benefits from reduced relative density, which increases flexibility and accelerates light-driven deformation. By employing sequential laser scanning, the LSMR achieves various locomotion modes, including linear peristalsis, in situ rotation, and hopping, through adjustments in scanning frequency, trajectory, and laser power. The LSMR achieves a continuous in situ rotation speed of 29.38°/s, nearly 30 times faster than previous studies, and exhibits a peristaltic locomotion speed of 15.15 μm/s (0.14 body lengths per second). The LSMR can autonomously perform programmed motions under closed-loop feedback control and navigate through narrow openings as small as 75% of its resting width by actively deforming. Compared to a solid microrobot, the lattice microrobot requires only one-sixth of the laser energy to achieve three times the motion speed, under otherwise identical conditions. These advancements mark a significant leap forward in the design and functionality of light-driven soft microrobots, offering promising avenues for future research in biomedicine, bionics, and micromechanical engineering.

Fig. 1. Design and manufacturing of LSMR.

a Schematic illustrating the system of the lattice microstructure LDW fabrication and vision-based closed-loop feedback system. b Schematic diagram of the process of releasing the microrobot after LDW fabrication. c The schematic diagram illustrates the LSMR in the application scenario of multimodal locomotion. d 3D model and SEM image of truncated octahedral lattice structures (rod length L of 8 μm, rod diameter D of 8 μm) arrays and image of individual microstructures. e Optical micrograph, 3D model, and SEM image of truncated octahedrons (rod length L of 4 μm, rod diameter D of 4 μm) composed of bionic fish shapes in LSMR.

Fig. 2. Design and light response of LSMR.

a Schematic illustrating the truncated octahedral lattice metamaterial microstructure array model and the monolithic model. b Optical microscopy images and finite element simulations of the lattice structure (L2D2) in the swollen and light-driven shrinking states. Scale bar: 50 μm. c Optical microscopy images and finite element simulations of the solid structure in the swollen and light-driven shrinking states. Scale bar: 50 μm. d Shrinkage ratios for lattice structures with different parameters. Data points with the same color and symbol represent unit microstructures with the same rod length L. Specifically, red squares, green circles, cyan downward triangles, and dark blue diamonds correspond to rod lengths of 2 μm, 4 μm, 6 μm, and 8 μm, respectively. Error bars represent standard deviation. e Comparison of light-driven deformation speed between lattice and solid structures. The blue background means the laser is off, and the yellow background means the laser is on. f Force-displacement curves for lattice and solid structures with the rod length of 6 μm.

Fig. 3. Linear peristalsis of LSMR under laser scanning frequency modulation.

a Optical microscopy images of scanning light-driven LSMR linear peristalsis (top view) and schematic illustrating the relative position of the laser (side view). b Front and end displacements in four laser scanning cycles. The blue background and yellow background in the figure represent one laser scanning cycle each. c Displacement of the front and end of the LSMR within a single laser scanning cycle. d, e Experimental images of light-driven linear peristalsis of the solid robot (300 mW) and lattice robot (50 mW). f Displacement of solid microrobot and lattice microrobot. g The average speed of solid microrobot and lattice microrobot. The initial 2 s is excluded from the analysis due to the jitter.

Fig. 4. Planar composite movement of LSMR modulated by laser trajectory.

a Schematic of the linear peristalsis. Gradual color change of the light path (from white to red) represents the laser scanning trajectory. The yellow arrow represents the direction of laser scanning. b Superimposed images of continuous linear peristalsis. c Displacement of continuous linear peristalsis at different time points. d Schematic of laser-actuated region for in situ rotation. e Sequential optical images of clockwise rotation processes. f Rotation angle over time and center-point offset in X and Y directions during rotation. g Schematic of squeezing through the slit. The red fluorescent line represents the scanning path of the laser. h Sequential optical images of the LSMR squeezing through the slit by active body deformation.

Fig. 5. Closed-loop control of the peristalsis.

a Schematic of manual and closed-loop control. b Microscopy image sequences of H-path motion under manual control, with red trace indicating laser scanning path. c Microscopy image sequences of pentagram path motion under closed-loop control. The white line represents the LSMR trajectory. Blue dots represent target points, and the numbers represent target point sequences. d Microscopy image sequences of maze path motion under closed-loop control. The area of the maze is marked in yellow. Scale bar: 200 μm.

Fig. 6. High-power laser-driven LSMR continuous hopping.

a Schematic illustration of the laser-driven LSMR performing linear continuous hopping. b Superimposed images of continuous linear hopping and (c) displacement with respect to time. d Schematic of laser action region for right-turn continuous hopping. e Superimposed images of right-turn hopping and (f) displacement with respect to time. g The stitched movement path of the fish-shaped LSMR maneuvering through the maze driven by continuous hopping. h Summary of reported robots plotted as the ratio of locomotion speed to body length as a function of length.