Acousto-Photolithography for Programmable Shape Deformation of Composite Hydrogel Sheets

Stimuli-responsive hydrogels with programmable shapes produced by defined patterns of particles are of great interest for the fabrication of small-scale soft actuators and robots. Patterning the particles in the hydrogels generally requires external magnetic or electric fields, thus limiting the material choice for the particles. However, acoustically driven particle manipulation depends on the acoustic impedance difference between the particles and the surrounding fluid, making it a more versatile method to spatially control particles. Here, we introduce the combination of acoustic force to align photothermal particles and photolithography to spatially immobilize these alignments within a temperature-responsive poly(N-isopropylacrylamide) hydrogel to trigger shape deformation under temperature change and light exposure. The spatial distribution of particles can be tuned by the power and frequency of the acoustic waves. Specifically, changing the spacing between the particle patterns and position alters the bending curvature and direction of this composite hydrogel sheet, respectively. Further, this acousto-photolithography provides a means of spatiotemporal programming of the internal heterogeneity of composite polymeric systems.