4D-printed soft microrobots: manufacturing, materials, actuation and applications

4D printing couples additive manufacturing with stimuli-responsive materials to create soft microrobots that can be programmed to change their shape, properties, and functions in response to external cues. This review synthesizes the core blueprint for 4D-printed soft microrobots, encompassing printing technologies, smart materials, and stimulus modalities. We explore how these elements collectively design locomotion, manipulation, and sensing at the microscale, and investigate application frontiers including targeted drug delivery, tissue engineering, stents, sensing, and other applications. Despite rapid progress, key obstacles remain, such as resolution-throughput-multimaterial trade-offs, interlayer adhesion, long-term fidelity, limited force density, biocompatibility, near-body-temperature triggers, and closed-loop imaging and navigation. Our conclusion is that 4D printing provides a unifying platform for adaptive, reconfigurable soft microrobots, and coordinated advances in materials, manufacturing, modeling, and regulation are essential for unlocking reliable clinical and industry-relevant systems.