Four-dimensional direct laser writing of reconfigurable compound micromachines

TLDR

Reconfigurable micromachines hold promise for biomedical uses, yet building small‑scale 3D structures with high shape‑morphing freedom remains difficult due to limited materials and fabrication methods. The study introduces a four‑dimensional microprinting approach that builds 3D‑to‑3D shape‑morphing micromachines in a single‑material, single‑step process. Using direct laser writing, stimulus‑responsive hydrogels are spatially patterned into sub‑micrometer 3D shapes, with crosslinking density, stiffness, and swelling tuned by femtosecond laser dosage and modeled by finite‑element analysis to predict morphing behavior. The resulting micromachines exhibit rapid, precise, reversible 3D‑to‑3D shape changes with high deformation‑amplifying effectiveness, making them promising multifunctional devices for engineering applications.

Abstract

Reconfigurable micromachines that are highly conscious of changing environments have significant potential for use in biomedical applications, such as minimally invasive surgery, cell manipulation, and tissue engineering. Current nanofabrication approaches with sophisticated designs appear to enhance the controllability of shape transformations, such as bending, folding, and twisting, while minimizing the response time. However, the construction of three-dimensional (3D) structures at a small scale with a high shape-morphing freedom poses challenges because of the lack of applicable materials and effective fabrication techniques. Here, we develop an advanced four-dimensional microprinting strategy for constructing 3D-to-3D shape-morphing micromachines in a single-material-single-step mode. Using direct laser writing, heterogeneous stimulus-responsive hydrogels can be distributed spatially into arbitrary 3D shapes with sub-micrometer features. The material crosslinking densities, stiffnesses, and swelling/shrinking degrees can be modulated by programming the exposure dosage of femtosecond laser pulses and characterized to predict the shape-morphing behaviors via finite-element methods. With our proposed approach, complex 3D reconfigurable compound micromachines with mechanical advantages, which exhibit an excellent deformation-amplifying effectiveness, can be constructed to achieve a rapid, precise, and reversible 3D-to-3D shape transformation in response to multiple external stimuli, and they emerge as promising smart and multifunctional micromachine candidates for various engineering applications.