基於擠壓的3D列印技術，例如直接墨水寫入（Direct ink writing, DIW），是一種新興的技術，用於製造具有先進應用的軟性材料。雖然一些離子凝膠已經成功應用於軟體機器人的人工肌肉製造中，但在沒有支撐材料的情況下，DIW列印複雜幾何形狀仍存在挑戰。此外大多數離子凝膠的機械強度較弱。本研究介紹了一種簡單的策略，用於製備可3D列印且具有韌性的離子凝膠，並可任意重新塑形。
本項目的3D列印的墨水中，是將單寧酸修飾的纖維素奈米晶體分散在聚乙烯醇的水溶液所製成。列印後，墨水經歷冷凍循環，通過聚乙烯醇的結晶形成柔軟而可伸縮的水凝膠。而列印後的平面結構水凝膠，可被重新配置成所需的3D形狀。隨後水凝膠內的水分子被單寧酸-深共熔溶劑交換出來，該溶劑由單寧酸溶解在深共熔溶劑，而深共熔溶劑由氯化膽鹼和甘油組成。這種溶劑交換過程觸發聚乙烯醇的結晶，從而形成具有高機械強度和所需幾何形狀的離子凝膠。此外溶劑交換促進了更多單寧酸與聚乙烯醇/深共熔溶劑之間的相互作用，增強了鍵結作用力和整體韌性的改善。
所開發的方法用於製造軟體機器人的人工肌肉，並使用簡單的氣動技術驅動。本研究提供了一種溶劑輔助鍵合方法，克服了離子凝膠的常見限制，擴展了軟體機器人的人工肌肉設計可能性。

Extrusion-based 3D printing, such as direct ink writing (DIW), is an emerging technique for fabricating soft materials with advanced applications. While some ionogels have been successfully used in soft robots for artificial muscle fabrication, DIW printing of complex geometries without supporting materials poses challenges. Additionally, most ionogels exhibit weak mechanical toughness. This work introduces a simple strategy for preparing 3D printable and tough ionogels that can adapt to arbitrary topographies.
The ink used for 3D printing consists of tannic acid-modified cellulose nanocrystals (TA-CNCs) dispersed in an aqueous solution of polyvinyl alcohol (PVA). After printing, the ink underwent a freeze-thaw process, forming soft yet stretchable hydrogels through PVA crystallization. Planar hydrogels were then reconfigured into desired 3D shapes. Subsequently, the water molecules inside the hydrogel were exchanged with tannic acid-deep eutectic solvent. The solvent was prepared by dissolving tannic acid in a deep eutectic solvent consisting of choline chloride and glycerol. This solvent exchange process triggered PVA crystallization, leading to the formation of ionogels with high mechanical toughness and the desired geometries. Moreover, the solvent exchange promotes more TA to increase interactions PVA/DES, resulting in stronger bonding and improved overall toughness.
The developed method was implemented to fabricate artificial muscles that were driven using simple pneumatic techniques. This work provides a solvent-assisted bonding strategy that overcame common limitations of ionogels and expanded the design possibilities for artificial muscles of soft robots.

(1) Abbott, A. P.; Capper, G.; Davies, D. L.; Rasheed, R. K.; Tambyrajah, V. Novel solvent properties of choline chloride/urea mixtures. Chemical Communications 2003, (1), 70-71.
(2) Zhang, Q.; Vigier, K. D. O.; Royer, S.; Jérôme, F. Deep eutectic solvents: syntheses, properties and applications. Chemical Society Reviews 2012, 41 (21), 7108-7146.
(3) Gurkan, B.; Squire, H.; Pentzer, E. Metal-free deep eutectic solvents: Preparation, physical properties, and significance. The Journal of Physical Chemistry Letters 2019, 10 (24), 7956-7964.
(4) Lomba, L.; García, C. B.; Ribate, M.; Giner, B.; Zuriaga, E. Applications of deep eutectic solvents related to health, synthesis, and extraction of natural based chemicals. Applied Sciences 2021, 11 (21), 10156.
(5) Hansen, F. A.; Pedersen-Bjergaard, S. Emerging extraction strategies in analytical chemistry. Analytical Chemistry 2019, 92 (1), 2-15.
(6) Yu, D.; Xue, Z.; Mu, T. Deep eutectic solvents as a green toolbox for synthesis. Cell Reports Physical Science 2022, 100809.
(7) Abbott, A. P.; Barron, J. C.; Ryder, K. S.; Wilson, D. Eutectic‐based ionic liquids with metal‐containing anions and cations. Chemistry–A European Journal 2007, 13 (22), 6495-6501.
(8) Mannu, A.; Blangetti, M.; Baldino, S.; Prandi, C. Promising technological and industrial applications of deep eutectic systems. Materials 2021, 14 (10), 2494.
(9) Abranches, D. O.; Martins, M. A.; Silva, L. P.; Schaeffer, N.; Pinho, S. P.; Coutinho, J. A. Phenolic hydrogen bond donors in the formation of non-ionic deep eutectic solvents: the quest for type V DES. Chemical Communications 2019, 55 (69), 10253-10256.
(10) Liu, Y.; Friesen, J. B.; McAlpine, J. B.; Lankin, D. C.; Chen, S.-N.; Pauli, G. F. Natural deep eutectic solvents: properties, applications, and perspectives. Journal of Natural Products 2018, 81 (3), 679-690.
(11) Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep eutectic solvents (DESs) and their applications. Chemical Reviews 2014, 114 (21), 11060-11082.
(12) Tomé, L. C.; Mecerreyes, D. Emerging ionic soft materials based on deep eutectic solvents. The Journal of Physical Chemistry B 2020, 124 (39), 8465-8478.
(13) Pettersson, F.; Remonen, T.; Adekanye, D.; Zhang, Y.; Wilén, C. E.; Österbacka, R. Environmentally friendly transistors and circuits on paper. ChemPhysChem 2015, 16 (6), 1286-1294.
(14) Zainal-Abidin, M. H.; Hayyan, M.; Ngoh, G. C.; Wong, W. F.; Looi, C. Y. Emerging frontiers of deep eutectic solvents in drug discovery and drug delivery systems. Journal of Controlled Release 2019, 316, 168-195.
(15) Li, T.; Song, Y.; Xu, J.; Fan, J. A hydrophobic deep eutectic solvent mediated sol-gel coating of solid phase microextraction fiber for determination of toluene, ethylbenzene and o-xylene in water coupled with GC-FID. Talanta 2019, 195, 298-305.
(16) Fan, H.; Wang, L.; Feng, X.; Bu, Y.; Wu, D.; Jin, Z. Supramolecular hydrogel formation based on tannic acid. Macromolecules 2017, 50 (2), 666-676.
(17) Kumar, N.; Goel, N. Phenolic acids: Natural versatile molecules with promising therapeutic applications. Biotechnology Reports 2019, 24, e00370.
(18) Wang, H.; Wang, C.; Zou, Y.; Hu, J.; Li, Y.; Cheng, Y. Natural polyphenols in drug delivery systems: Current status and future challenges. Giant 2020, 3, 100022.
(19) Liu, X.; Ma, Y.; Zhang, X.; Huang, J. Cellulose nanocrystal reinforced conductive nanocomposite hydrogel with fast self-healing and self-adhesive properties for human motion sensing. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2021, 613, 126076.
(20) Zhang, Z.; Xie, L.; Ju, Y.; Dai, Y. Recent advances in metal‐phenolic networks for cancer theranostics. Small 2021, 17 (43), 2100314.
(21) Bigham, A.; Rahimkhoei, V.; Abasian, P.; Delfi, M.; Naderi, J.; Ghomi, M.; Moghaddam, F. D.; Waqar, T.; Ertas, Y. N.; Sharifi, S. Advances in tannic acid-incorporated biomaterials: Infection treatment, regenerative medicine, cancer therapy, and biosensing. Chemical Engineering Journal 2022, 432, 134146.
(22) Meyabadi, T. F.; Dadashian, F.; Sadeghi, G. M. M.; Asl, H. E. Z. Spherical cellulose nanoparticles preparation from waste cotton using a green method. Powder Technology 2014, 261, 232-240.
(23) Du, H.; Liu, W.; Zhang, M.; Si, C.; Zhang, X.; Li, B. Cellulose nanocrystals and cellulose nanofibrils based hydrogels for biomedical applications. Carbohydrate Polymers 2019, 209, 130-144.
(24) Ratajczak, K.; Stobiecka, M. High-performance modified cellulose paper-based biosensors for medical diagnostics and early cancer screening: A concise review. Carbohydrate Polymers 2020, 229, 115463.
(25) Foroughi, F.; Rezvani Ghomi, E.; Morshedi Dehaghi, F.; Borayek, R.; Ramakrishna, S. A review on the life cycle assessment of cellulose: From properties to the potential of making it a low carbon material. Materials 2021, 14 (4), 714.
(26) Moon, R. J.; Martini, A.; Nairn, J.; Simonsen, J.; Youngblood, J. Cellulose nanomaterials review: structure, properties and nanocomposites. Chemical Society Reviews 2011, 40 (7), 3941-3994.
(27) Siqueira, G.; Kokkinis, D.; Libanori, R.; Hausmann, M. K.; Gladman, A. S.; Neels, A.; Tingaut, P.; Zimmermann, T.; Lewis, J. A.; Studart, A. R. Cellulose nanocrystal inks for 3D printing of textured cellular architectures. Advanced Functional Materials 2017, 27 (12), 1604619.
(28) Bangar, S. P.; Harussani, M.; Ilyas, R.; Ashogbon, A. O.; Singh, A.; Trif, M.; Jafari, S. M. Surface modifications of cellulose nanocrystals: Processes, properties, and applications. Food Hydrocolloids 2022, 107689.
(29) Macke, N.; Hemmingsen, C. M.; Rowan, S. J. The effect of polymer grafting on the mechanical properties of PEG‐grafted cellulose nanocrystals in poly (lactic acid). Journal of Polymer Science 2022.
(30) Kedzior, S. A.; Zoppe, J. O.; Berry, R. M.; Cranston, E. D. Recent advances and an industrial perspective of cellulose nanocrystal functionalization through polymer grafting. Current Opinion in Solid State and Materials Science 2019, 23 (2), 74-91.
(31) Araki, J.; Wada, M.; Kuga, S. Steric stabilization of a cellulose microcrystal suspension by poly (ethylene glycol) grafting. Langmuir 2001, 17 (1), 21-27.
(32) Vakili, M. R.; Mohammed-Saeid, W.; Aljasser, A.; Hopwood-Raja, J.; Ahvazi, B.; Hrynets, Y.; Betti, M.; Lavasanifar, A. Development of mucoadhesive hydrogels based on polyacrylic acid grafted cellulose nanocrystals for local cisplatin delivery. Carbohydrate Polymers 2021, 255, 117332.
(33) Hu, Z.; Berry, R. M.; Pelton, R.; Cranston, E. D. One-pot water-based hydrophobic surface modification of cellulose nanocrystals using plant polyphenols. ACS Sustainable Chemistry & Engineering 2017, 5 (6), 5018-5026.
(34) DeMerlis, C.; Schoneker, D. Review of the oral toxicity of polyvinyl alcohol (PVA). Food and Chemical Toxicology 2003, 41 (3), 319-326.
(35) Maria, T. M.; De Carvalho, R. A.; Sobral, P. J.; Habitante, A. M. B.; Solorza-Feria, J. The effect of the degree of hydrolysis of the PVA and the plasticizer concentration on the color, opacity, and thermal and mechanical properties of films based on PVA and gelatin blends. Journal of Food Engineering 2008, 87 (2), 191-199.
(36) Wang, L.; Periyasami, G.; Aldalbahi, A.; Fogliano, V. The antimicrobial activity of silver nanoparticles biocomposite films depends on the silver ions release behaviour. Food Chemistry 2021, 359, 129859.
(37) Halima, N. B. Poly (vinyl alcohol): review of its promising applications and insights into biodegradation. RSC Advances 2016, 6 (46), 39823-39832.
(38) Wang, Y.; Wang, J.; Ma, Z.; Yan, L. A highly conductive, self-recoverable, and strong eutectogel of a deep eutectic solvent with polymer crystalline domain regulation. ACS Applied Materials & Interfaces 2021, 13 (45), 54409-54416.
(39) Ricciardi, R.; Auriemma, F.; De Rosa, C.; Lauprêtre, F. X-ray diffraction analysis of poly (vinyl alcohol) hydrogels, obtained by freezing and thawing techniques. Macromolecules 2004, 37 (5), 1921-1927.
(40) Peppas, N. A.; Mongia, N. K. Ultrapure poly (vinyl alcohol) hydrogels with mucoadhesive drug delivery characteristics. European Journal of Pharmaceutics and Biopharmaceutics 1997, 43 (1), 51-58.
(41) Wahab, A. H. A.; Saad, A. P. M.; Harun, M. N.; Syahrom, A.; Ramlee, M. H.; Sulong, M. A.; Kadir, M. R. A. Developing functionally graded PVA hydrogel using simple freeze-thaw method for artificial glenoid labrum. Journal of the mechanical behavior of biomedical materials 2019, 91, 406-415.
(42) Waresindo, W. X.; Luthfianti, H. R.; Priyanto, A.; Hapidin, D. A.; Edikresnha, D.; Aimon, A. H.; Suciati, T.; Khairurrijal, K. Freeze–thaw hydrogel fabrication method: basic principles, synthesis parameters, properties, and biomedical applications. Materials Research Express 2023.
(43) Jiang, S.; Liu, S.; Feng, W. PVA hydrogel properties for biomedical application. Journal of the mechanical behavior of biomedical materials 2011, 4 (7), 1228-1233.
(44) Adelnia, H.; Ensandoost, R.; Moonshi, S. S.; Gavgani, J. N.; Vasafi, E. I.; Ta, H. T. Freeze/thawed polyvinyl alcohol hydrogels: Present, past and future. European Polymer Journal 2022, 164, 110974.
(45) Chen, J.; Yang, Z.; Shi, D.; Zhou, T.; Kaneko, D.; Chen, M. High strength and toughness of double physically cross‐linked hydrogels composed of polyvinyl alcohol and calcium alginate. Journal of Applied Polymer Science 2021, 138 (10), 49987.
(46) Zhang, H.; Tang, N.; Yu, X.; Li, M. H.; Hu, J. Strong and tough physical eutectogels regulated by the spatiotemporal expression of non‐covalent interactions. Advanced Functional Materials 2022, 32 (41), 2206305.
(47) Wang, Y.; Liu, Y.; Plamthottam, R.; Tebyetekerwa, M.; Xu, J.; Zhu, J.; Zhang, C.; Liu, T. Highly stretchable and reconfigurable ionogels with unprecedented thermoplasticity and ultrafast self-healability enabled by gradient-responsive networks. Macromolecules 2021, 54 (8), 3832-3844.
(48) Campbell, T. Could 3D printing change the world?: Technologies, potential, and implications of additive manufacturing. 2011.
(49) Melchels, F. P.; Feijen, J.; Grijpma, D. W. A review on stereolithography and its applications in biomedical engineering. Biomaterials 2010, 31 (24), 6121-6130.
(50) Yilmaz, B.; Al Rashid, A.; Mou, Y. A.; Evis, Z.; Koç, M. Bioprinting: A review of processes, materials and applications. Bioprinting 2021, 23, e00148.
(51) Ngo, T. D.; Kashani, A.; Imbalzano, G.; Nguyen, K. T.; Hui, D. Additive manufacturing (3D printing): A review of materials, methods, applications and challenges. Composites Part B: Engineering 2018, 143, 172-196.
(52) Wang, X.; Jiang, M.; Zhou, Z.; Gou, J.; Hui, D. 3D printing of polymer matrix composites: A review and prospective. Composites Part B: Engineering 2017, 110, 442-458.
(53) Kim, G. B.; Lee, S.; Kim, H.; Yang, D. H.; Kim, Y.-H.; Kyung, Y. S.; Kim, C.-S.; Choi, S. H.; Kim, B. J.; Ha, H. Three-dimensional printing: basic principles and applications in medicine and radiology. Korean Journal of Radiology 2016, 17 (2), 182-197.
(54) Masood, S.; Song, W. Development of new metal/polymer materials for rapid tooling using fused deposition modelling. Materials & Design 2004, 25 (7), 587-594.
(55) Sood, A. K.; Ohdar, R. K.; Mahapatra, S. S. Parametric appraisal of mechanical property of fused deposition modelling processed parts. Materials & Design 2010, 31 (1), 287-295.
(56) Fu, K.; Wang, Y.; Yan, C.; Yao, Y.; Chen, Y.; Dai, J.; Lacey, S.; Wang, Y.; Wan, J.; Li, T. Graphene oxide‐based electrode inks for 3D‐printed lithium‐ion batteries. Advanced Materials 2016, 28 (13), 2587-2594.
(57) Solís Pinargote, N. W.; Smirnov, A.; Peretyagin, N.; Seleznev, A.; Peretyagin, P. Direct ink writing technology (3d printing) of graphene-based ceramic nanocomposites: A review. Nanomaterials 2020, 10 (7), 1300.
(58) Wan, X.; Luo, L.; Liu, Y.; Leng, J. Direct ink writing based 4D printing of materials and their applications. Advanced Science 2020, 7 (16), 2001000.
(59) Eqtesadi, S.; Motealleh, A.; Miranda, P.; Lemos, A.; Rebelo, A.; Ferreira, J. M. A simple recipe for direct writing complex 45S5 Bioglass® 3D scaffolds. Materials Letters 2013, 93, 68-71.
(60) Shiva, A.; Stilli, A.; Noh, Y.; Faragasso, A.; De Falco, I.; Gerboni, G.; Cianchetti, M.; Menciassi, A.; Althoefer, K.; Wurdemann, H. A. Tendon-based stiffening for a pneumatically actuated soft manipulator. IEEE Robotics and Automation Letters 2016, 1 (2), 632-637.
(61) Pawlowski, B.; Sun, J.; Xu, J.; Liu, Y.; Zhao, J. Modeling of soft robots actuated by twisted-and-coiled actuators. IEEE/ASME Transactions on Mechatronics 2018, 24 (1), 5-15.
(62) Rus, D.; Tolley, M. T. Design, fabrication and control of soft robots. Nature 2015, 521 (7553), 467-475.
(63) Skorina, E. H.; Luo, M.; Oo, W. Y.; Tao, W.; Chen, F.; Youssefian, S.; Rahbar, N.; Onal, C. D. Reverse pneumatic artificial muscles (rPAMs): Modeling, integration, and control. PloS one 2018, 13 (10), e0204637.
(64) Zhao, H.; Li, Y.; Elsamadisi, A.; Shepherd, R. Scalable manufacturing of high force wearable soft actuators. Extreme Mechanics Letters 2015, 3, 89-104.
(65) Laschi, C.; Cianchetti, M.; Mazzolai, B.; Margheri, L.; Follador, M.; Dario, P. Soft robot arm inspired by the octopus. Advanced robotics 2012, 26 (7), 709-727.
(66) Shih, B.; Christianson, C.; Gillespie, K.; Lee, S.; Mayeda, J.; Huo, Z.; Tolley, M. T. Design considerations for 3D printed, soft, multimaterial resistive sensors for soft robotics. Frontiers in Robotics and AI 2019, 6, 30.
(67) Walker, J.; Zidek, T.; Harbel, C.; Yoon, S.; Strickland, F. S.; Kumar, S.; Shin, M. Soft robotics: A review of recent developments of pneumatic soft actuators. In Actuators, 2020; MDPI: Vol. 9, p 3.
(68) Drotman, D.; Jadhav, S.; Sharp, D.; Chan, C.; Tolley, M. T. Electronics-free pneumatic circuits for controlling soft-legged robots. Science Robotics 2021, 6 (51), eaay2627.
(69) Zhang, P.; Zhang, C.; Wang, S.; Chen, Z. Motion characteristic and analysis of bionic jellyfish with fluid-driven soft actuator. In 2020 15th IEEE Conference on Industrial Electronics and Applications (ICIEA), 2020; Cai, Z., Ed.; IEEE: pp 1684-1689.
(70) Wang, J.; Gao, D.; Lee, P. S. Recent progress in artificial muscles for interactive soft robotics. Advanced Materials 2021, 33 (19), 2003088.
(71) Li, S.; Vogt, D. M.; Rus, D.; Wood, R. J. Fluid-driven origami-inspired artificial muscles. Proceedings of the National academy of Sciences 2017, 114 (50), 13132-13137.
(72) Daerden, F.; Lefeber, D. Pneumatic artificial muscles: actuators for robotics and automation. European Journal of Mechanical and Enviromental Engineering 2002, 47 (1), 11-22.
(73) Yang, D.; Verma, M. S.; So, J. H.; Mosadegh, B.; Keplinger, C.; Lee, B.; Khashai, F.; Lossner, E.; Suo, Z.; Whitesides, G. M. Buckling pneumatic linear actuators inspired by muscle. Advanced Materials Technologies 2016, 1 (3), 1600055.
(74) Schenk, M.; Guest, S. D. Geometry of Miura-folded metamaterials. Proceedings of the National Academy of Sciences 2013, 110 (9), 3276-3281.
(75) Hanif, Z.; Khan, Z. A.; Tariq, M. Z.; Choi, D.; Park, S. J. Coatable tannic acid-deposited cellulose nanocrystals for Fe (III) sensing and its application to a facile, scalable and portable sensing platform. Dyes and Pigments 2021, 196, 109732.
(76) Peng, E.; Zhang, D.; Ding, J. Ceramic robocasting: recent achievements, potential, and future developments. Advanced Materials 2018, 30 (47), 1802404.
(77) Chen, Y.-N.; Jiao, C.; Zhao, Y.; Zhang, J.; Wang, H. Self-assembled polyvinyl alcohol–tannic acid hydrogels with diverse microstructures and good mechanical properties. ACS Omega 2018, 3 (9), 11788-11795.
(78) Kandhola, G.; Djioleu, A.; Rajan, K.; Labbé, N.; Sakon, J.; Carrier, D. J.; Kim, J.-W. Maximizing production of cellulose nanocrystals and nanofibers from pre-extracted loblolly pine kraft pulp: a response surface approach. Bioresources and Bioprocessing 2020, 7 (1), 1-16.
(79) Yang, S.; Wu, W.; Jiao, Y.; Cai, Z.; Fan, H. Preparation of NBR/Tannic acid composites by assembling a weak IPN structure. Composites Science and Technology 2017, 153, 40-47.
(80) Peng, M.; Xiao, G.; Tang, X.; Zhou, Y. Hydrogen-bonding assembly of rigid-rod poly (p-sulfophenylene terephthalamide) and flexible-chain poly (vinyl alcohol) for transparent, strong, and tough molecular composites. Macromolecules 2014, 47 (23), 8411-8419.