Rapid 4D printing of hydrogel microactuators by single-exposure of femtosecond structured beams

Femtosecond laser direct writing (FLDW) method enables the flexible three-dimensional (3D) molding of intelligent microactuators with submicron resolution, which are capable of adaptive deformation when exposed to external stimuli. However, their mass production is still limited by complicated, multi-material composites or time-consuming programmed point-by-point scanning strategies to date. Here, a novel four-dimensional (4D) printing method based on two-photon polymerization is proposed to achieve the rapid molding of hydrogel microactuators. Wavefront and amplitude co-modulation based on a spatial light modulator is introduced into the architecture of 4D printing, thus endowing the hydrogel material with adaptive shape morphing function with a single exposure. The processing efficiency is improved by  2 orders of magnitude, providing higher throughput and large-area manufacturing capability. This approach allows for the efficient prototyping of microgrippers with controllable bending properties for in-situ capture of polystyrene microspheres. Moreover, the microtube arrays can serve as 3D cell culture scaffolds, enabling the rapid construction of large-scale cell growth environment. Altogether, this flexible, customizable, and high-throughput 4D printing strategy paves the way for the construction of intelligent microactuators with promising applications in particle manipulation, biomedicine, tissue engineering, and other fields.