Femtosecond Laser Writing of Stepwise Detachable and Biodegradable Microrobots for Adjustable Locomotion and Drug Delivery.

Inspired by natural organisms' controllable detachment, various detachable robots have been engineered toward targeted cargo delivery and environmental sensing. However, creating stepwise detachable and degradable robots at the microscale remains challenging. Herein, we report stepwise detachable and degradable microrobots (∼50 µm) fabricated from a single hydrogel using spatially graded direct laser writing (SGDLW), much smaller than previously reported detachable robots. SGDLW precisely controls local laser exposure dose, thereby programming microstructure crosslinking density, resulting in controllable cross-sectional porosity ranging from 17.6% to 37.2%, and ultimately adjusting the degradation time (from 2 min to 44 min). By encoding different local crosslinking densities, microstructures capable of single-step detachment are designed, including artificial microflowers, microdandelions, and microfish eggs. Moreover, multi-step detachment of microtrees and microdandelions can be achieved with minute-scale temporal programmability. Finally, bioinspired microrobots demonstrate promising functionalities of adjustable locomotion and drug delivery, underscoring their potential in microrobotics and targeted drug delivery.