Programmable Microscale Actuation of Hydrogels with Tunable Response via Printing on Particles

Two-photon polymerization (2PP) enables high-resolution additive manufacturing of hydrogel-based microscale actuators, advancing soft robotics, microfluidics, and biomedical engineering. However, achieving precise and programmable deformations at this length scale remains challenging. Existing routes to fabricate hydrogel systems exhibit limited design flexibility to incorporate multiple materials with tailored responses. Here, we introduce a versatile microscale printing approach combining 2PP with capillarity-assisted particle assembly (CAPA) to create particle-templated hydrogels exhibiting systematically tunable volume phase transition temperatures (VPTTs) ranging from 23 °C to 60 °C. This tunability, achieved through controlled polymer hydrophilicity-hydrophobicity balance, allows precise thermal actuation. We further integrate rigid resins alongside responsive hydrogels in the 2PP process, achieving spatially defined mechanical heterogeneity and localized multi-stage actuation. Finally, we demonstrate that by adding pH-dependent charge modulation, we can induce hysteresis during swelling-deswelling actuation cycles and thus enable anisotropic deformation in response to environmental cues. Our multi-material printing strategy significantly expands the capabilities of microscale actuation, promising advanced applications in soft robotics, adaptive biomedical devices, dynamic microfluidics, and responsive photonics.