One-Step, Rapid 3D Printing of Multi-Stimuli-Responsive Bilayer Structures for Microscale Actuators and Sensors

Microscale stimuli-responsive structures play an important role in micromechanical systems as they can serve as sensors or actuators ^1-5. However, the development of simple and rapid methods for their fabrication remains an unsolved challenge^6-8. Here, we present a one-step, bi-material 3D printing method for fabricating multi-stimuli-responsive microactuators⁹. A two-phase femtoliter meniscus formed on a theta micropipette is used to print a freestanding bilayer microstructure with programmed shape and composition, which undergoes an asymmetric volume change upon the adsorption or desorption of water. The printed bilayer structures exhibit reversible, preprogrammed actuation under time-varying humidity and infrared (IR) light stimuli. Furthermore, the method provides unprecedented process simplicity in multi-segmented structuring, configuring useful microscale moves such as gripping micro-objects. In this talk, I will also discuss the potential of our method to afford a diverse class of smart-bilayer devices such as actuators, sensors, and energy harvesters, by diversifying printing materials.<br/><br/>1. M. Li, A. Pal, A. Aghakhani, A. Pena-Francesch and M. Sitti: Soft actuators for real-world applications. <i>Nature Reviews Materials</i> <b>7</b>, 235 (2022).<br/>2. C.S.X. Ng, M.W.M. Tan, C. Xu, Z. Yang, P.S. Lee and G.Z. Lum: Locomotion of Miniature Soft Robots. <i>Advanced Materials</i> <b>33</b>, 2003558 (2021).<br/>3. D. Melling, J.G. Martinez and E.W.H. Jager: Conjugated Polymer Actuators and Devices: Progress and Opportunities. <i>Advanced Materials</i> <b>31</b>, 1808210 (2019).<br/>4. S. Palagi and P. Fischer: Bioinspired microrobots. <i>Nature Reviews Materials</i> <b>3</b>, 113 (2018).<br/>5. X.-Q. Wang and G.W. Ho: Design of untethered soft material micromachine for life-like locomotion. <i>Materials Today</i> <b>53</b>, 197 (2022).<br/>6. X. Le, W. Lu, J. Zhang and T. Chen: Recent Progress in Biomimetic Anisotropic Hydrogel Actuators. <i>Advanced Science</i> <b>6</b>, 1801584 (2019).<br/>7. L. Hu, Y. Wan, Q. Zhang and M.J. Serpe: Harnessing the Power of Stimuli-Responsive Polymers for Actuation. <i>Advanced Functional Materials</i> <b>30</b>, 1903471 (2020).<br/>8. M. Ilami, H. Bagheri, R. Ahmed, E.O. Skowronek and H. Marvi: Materials, Actuators, and Sensors for Soft Bioinspired Robots. <i>Advanced Materials</i> <b>33</b>, 2003139 (2021).<br/>9. X. Huan, S. Lee, H. Lee, Z. Xu, J. Yang, M. Chen, Y. Liu and J.T. Kim: One-Step, Continuous Three-Dimensional Printing of Multi-Stimuli-Responsive Bilayer Microactuators via a Double-Barreled Theta Pipette. <i>ACS Applied Materials & Interfaces</i> <b>13</b>, 43396 (2021).