pH-responsive microgrippers with reversible actuation Yekaterina Tskhe , Srikanth Kolagatla, Alex J. Thompson, Colm Delaney, Larisa Florea 1 AMBER Centre and CRANN, School of Chemistry, Trinity College Dublin, College Green, Dublin 2, Ireland 2 Department of Surgery & Cancer, St Mary’s Hospital, Imperial College London, South Wharf Road, London, W2 1NY, UK 3 The Hamlyn Centre, Institute of Global Health Innovation (IGHI), Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, UK The application of additive manufacturing to the soft-robotics field has gained increasing attention in the recent years, in particular for the application of stimuli-responsive to garner actuation. This holds the potential for nano/ microscale tools to be manipulated with considerable control and dexterity, which proves particularly important in interaction with living matter. In this work, we highlight the use of direct laser writing via two photon polymerisation (2PP) for the fabrication of multi-material functional microgrippers. This allows for the creation of complex 3D microstructures with tuneable mechanical and chemical properties that can be actuated in response to chemical changes in their intimate environment. For instance, previously reported work on sugar-responsive polymers proved the application of such materials in the various 4D actuating microsystems. 1 We present a new adaptable pH-responsive photoresist for 2PP, which we characterise using optical microscopy, AFM, and SEM. Inspired by artificial musculoskeletal systems, which can mimic the contraction and expansion mechanism of our muscles using responsive polymer materials. 2 We then exploit this responsive hydrogel material as hinges in a microgripper. This work showcases arrays of microgrippers which demonstrate fast and reversible actuation in response to pH change. We will document the effect of photoresist composition, structure design, and fabrication parameters on the degree and speed of reversible actuation and opening/closing of the microgripper arrays. The potential application of such microgrippers can be found in cell manipulation, minimally invasive surgeries and sensing. 2PP-fabricated microgripper on optical fiber has already demonstrated the grasping of micro-objects and force sensing abilities, while it requires the application of external force. 3 In this work, we demonstrate how to fabricate and control novel programmable 4D micro-tools integrated with stimuli-responsive materials without the need of applied force. References 1. Ennis, A., Nicdao, D., Kolagatla, S., Dowling, L., Tskhe, Y., Thompson, A. J., Daniel Trimble, Colm Delaney & Florea, L. (2023). 2. Two-Photon Polymerization of Sugar Responsive 4D Microstructures. Advanced Functional Materials , 2213947.Ma, Z. C., Zhang, Y. L., Han, B., Hu, X. Y., Li, C. H., Chen, Q. D., & Sun, H. B. (2020). 3. Femtosecond laser programmed artificial musculoskeletal systems. Nature communications ,11(1), 4536.Power, M., Thompson, A. J., Anastasova, S., & Yang, G. Z. (2018). 4. A monolithic force-sensitive 3D microgripper fabricated on the tip of an optical fiber using 2‐photon polymerization. Small ,14(16), 1703964.
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