An acoustically actuated hydrogel shape-morphing micromachine

Bioinspired by the transformations of animals and plants such as pangolins and mimosas, many biomimetic shape-morphing systems have been developed. However, due to scale effect, microscale interactions become the dominant force, which may make the traditional shape-morphing systems ineffective. Acoustic actuation is expected to overcome this challenge. Here, we have developed an acoustically actuated hydrogel shape-morphing micromachine (AHSMM). It has a variable stiffness design, with the lower stiffness part serving as a flexible hinge to achieve transformation. Under the excitation of acoustic field, the flexible hinge produces strong oscillation and quickly provides the force and torque required for the transformation of AHSMM (generally less than 500 ms). In addition, we have developed a preprogrammed design for the transformation of micromachine to predict its transformation morphology. Furthermore, through the AHSMM, we have separately designed morphing transformations between Chinese characters (e.g., “夫” (fu) to “央” (yang)) and English letters (e.g., “k” to “x”). Finally, we developed a shape-morphing microrobot (width: 174.33 μm) utilizing this flexible hinge, which can pass through a narrow channel through its own shape-morphing, providing great potential in targeted drug delivery (the shape-morphing time is less than 100 ms, the forward speed can reach about 800 μm/s). Our work not only provides innovative ideas for shape-morphing design at the microscale, but also expands the coupling applications of acoustics, soft matter, and microrobots.