Aligned Magnetic Nanocomposites for Modularized and Recyclable Soft Microrobots

Abstract

Creating reconfigurable and recyclable soft microrobots that can execute multimodal locomotion has been a challenge due to the difficulties in material processing and structure engineering at a small scale. Here, we propose a facile technique to manufacture diverse soft microrobots (∼100 μm in all dimensions) by mechanically assembling modular magnetic microactuators into different three-dimensional (3D) configurations. The module is composed of a cubic micropillar supported on a square substrate, both made of elastomer matrix embedded with prealigned magnetic nanoparticle chains. By directionally bonding the sides or backs of identical modules together, we demonstrate that assemblies from only two and four modules can execute a wide range of locomotion, including gripping microscale objects, crawling and crossing solid obstacles, swimming within narrow and tortuous microchannels, and rolling along flat and inclined surfaces, upon applying proper magnetic fields. The assembled microrobots can additionally perform pick–transfer–place and cargo-release tasks at the microscale. More importantly, like the game of block-building, the microrobots can be disassembled back to separate modules and then reassembled to other configurations as demanded. The present study not only provides a versatile and economic manufacturing technique for reconfigurable and recyclable soft microrobots, enabling unlimited design space for diverse robotic locomotion from limited materials and module structures, but also extends the functionality and dexterity of existing soft robots to microscale that should facilitate practical applications at such small scale.

Recent Progress on the Development of Magnetically‐Responsive Micropillars: Actuation, Fabrication, and Applications

“…The deformation of the micropillar in a uniform magnetic field is driven by magnetic torque. [ 60,66,76,86 ] Upon applying a uniform field before curing, each magnetic nanoparticle dispersed within the liquid matrix suffers a magnetic torque moment [ 87 ] $$\[\begin{array}{*{20}{c}}{{{{\bf T}}_{mag}} = {{\bf m}} \times {{\bf B}}}\end{array}\]$$ where m is the magnetic dipolar moment of a single particle and B is the magnetic induction intensity of the uniform magnetic field. The particle is rotated by such a torque moment to align the magnetic polarization to the direction of the external magnetic field.…”

“…In a recent study, a concept of “modular assembly” for miniature soft robots was presented. [ 66 ] A single modular microactuator consisted of a cubic magnetic micropillar supported on a square substrate. Various micro‐robots with different functions could be fabricated by mechanically assembling the modules into different 3D configurations and subsequently the robots could be disassembled back to separate modules for next round of reassembly.…”

“…Magnetic micropillars refer to stimuli-responsive pillar-shaped microstructures that can undergo mechanical deformations upon applying external magnetic fields. The gradient magnetic fields [64,65] can apply magnetic forces on the magnetic materials to induce the deformations of the magnetic micropillars while the uniform magnetic fields [56,66] align the dipoles of the magnetic media within the pillars along the field directions to exert magnetic torques on the pillars. Metal micropillars serve as magnets that can bend toward the field direction upon applying a gradient magnetic field.…”

“…The deformation of the micropillar in a uniform magnetic field is driven by magnetic torque. [60,66,76,86] Upon applying a uniform field before curing, each magnetic…”

“…The biological cilia not only play a significant role in the transport processes within organisms, but also serve as feet for some microorganisms and arthropods, such as paramecium and millipedes for crawling, swimming, grasping, and climbing. [48,66,76,138] Magnetic swimming microrobots can perform various biomedical operations in the fluidic environment of biological systems due to their remote controllability and biocompatibility. The beating motion of the pillar legs in the fluid is shown in Figure 11A(i) and according to the calculation results of a simplified model, the maximum force during the power stroke was far greater than the maximum force during the recovery stroke.…”