Diffusion-guided 4D microprinting of soft microactuators.

Four-dimensional (4D) printing has emerged as a powerful strategy for creating reconfigurable soft actuators with applications in biomedical engineering and microrobotics. However, most existing methods, such as inkjet printing or photoalignment, are restricted to film-like or net-like architectures that only enable out-of-plane deformation and cannot be scaled to the microscale. Although two-photon polymerization provides submicron resolution and 3D microfabrication, its voxel-by-voxel laser scanning induces strong liquid crystal diffusion around each printed voxel, which cannot be effectively suppressed by external fields or laser-induced anchoring. Here, we harness this diffusion as a design principle for 4D microprinting of soft liquid crystal network microactuators, enabling hierarchical and volumetric alignment within complex 3D architectures. Diffusion-guided orientation emerges perpendicular to the printed surface profile, allowing programmed molecular alignment through controlled variation of the scanning direction. These microactuators incorporate volumetrically programmable 3D architectures and can be integrated into multi-jointed microarms and microgrippers, executing complex and coordinated actuations for advanced microrobotics.