4D printed multi-material soft actuators for spatiotemporal control Kun Zhou 1 , Rujie Sun 1 , Jonathan P. Wojciechowski 1 , Richard Wang 1 , Jonathan Yeow 1 , Yuyang Zuo 1 , Xin Song 1 , Chunliang Wang 1 , Yue Shao 1 , Molly M. Stevens 1,2,3* 1 Department of Materials, Imperial College London, UK, 2 Department of Bioengineering, Imperial College London, UK, 3 Institute of Biomedical Engineering, Imperial College London, UK Soft actuators (SAs) can spatiotemporally interact with delicate objects through optimised designs of materials and geometric configurations. Although various advanced fabrication techniques are used to fabricate SAs, 3D printing is the most popular method due to its diverse material compatibility and flexibility in structural designs to allow optimised configurations with sophisticated actuation patterns. However, existing 3D printed SAs have limited spatiotemporal control, and it is essential to integrate multiple functional materials with distinctive properties into one system to improve the robustness of the actuation mechanics. Herein, we present a 4D printed multi-material soft actuator (MMSA) that integrates movement, system switch, sensor, and actuator modalities in a single device to achieve controlled movement that is responsive to different environmental conditions. An interface design between hydrophobic and hydrophilic surfaces was first developed based on hydrophobic interaction and thiol-ene reaction. We next developed two types of material systems (a hydrophobic shape- memory polymer and a pH-responsive hydrogel) that form the basis of the MMSA. The hydrogel acted as a sensor and actuator that responded to surrounding pH changes by swelling or shrinking, whilst the shape memory polymer acted as the switch of the hydrogel to stabilise the hydrogel deformation on-demand via temperature or light triggers. The advantages of the proposed MMSA system were highlighted via a series of cargo capture- release demonstrations, validating its fabrication fidelity and active spatiotemporal control. The MMSA platform provides a promising research avenue for developing multifunctional SAs with potential applications in biomedical engineering and environmental engineering. References 1. M. Li, A. Pal, A. Aghakhani, A. Pena-Francesch, M. Sitti, Nat Rev Mater 2022 , 7, 235. 2. M. Cianchetti, C. Laschi, A. Menciassi, P. Dario, Nat Rev Mater 2018 , 3, 143. 3. Y. Kim, X. H. Zhao, Chem Rev 2022 , 122, 5317. 4. D. D. Jin, Q. Y. Chen, T. Y. Huang, J. Y. Huang, L. Zhang, H. L. Duan, Mater Today 2020 , 32, 19. 5. J. A. C. Liu, J. H. Gillen, S. R. Mishra, B. A. Evans, J. B. Tracy, Sci Adv 2019 , 5. 6. C. Y. Lo, Y. S. Zhao, C. Kim, Y. Alsaid, R. Khodambashi, M. Peet, R. Fisher, H. Marvi, S. Berman, D. Aukes, X. M. He, Mater Today 2021 , 50, 35. 7. D. Pan, D. Wu, P. J. Li, S. Y. Ji, X. Nie, S. Y. Fan, G. Y. Chen, C. C. Zhang, C. Xin, B. Xu, S. W. Zhu, Z. Cai, Y. L. Hu, J. W. Li, J. R. Chu, Adv Funct Mater 2021 , 31. 8. M. T. Li, X. Wang, B. Dong, M. Sitti, Nature Communications 2020 , 11.
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