刺激响应水凝胶软机器人的四维打印
Summary
这份手稿描述了一种4D打印策略，用于制造智能刺激响应软机器人。这种方法可以为促进智能形状可变形软机器人系统的实现提供基础，包括智能机械手、电子和医疗保健系统。
Abstract
本协议描述了使用三维（3D）生物打印方法创建四维（4D），时间依赖性，形状可变，刺激响应软机器人。最近，4D打印技术被广泛提出作为开发形状可变形软机器人的创新新方法。特别是，4D随时间变化的形状转换是软机器人中的一个重要因素，因为它允许在由外部线索（如热，pH和光）触发时在正确的时间和地点发生有效的功能。根据这一观点，可以打印刺激响应材料，包括水凝胶、聚合物和杂化材料，以实现智能形状可变形的软机器人系统。目前的协议可用于制造由 N-异丙基丙烯酰胺（NIPAM）基水凝胶组成的热响应软夹具，整体尺寸从毫米到厘米不等。预计本研究将为智能机械手（如抓手、执行器和拾取和放置机）、医疗保健系统（如药物胶囊、活检工具和显微手术）和电子（如可穿戴传感器和流体）等各种应用的智能软机器人系统提供新的方向。
Introduction
从技术和智力的角度来看，刺激响应软机器人的开发都很重要。术语刺激响应软机器人通常是指由水凝胶、聚合物、弹性体或混合体组成的设备/系统，这些设备/系统响应外部线索（如热量、pH 值和光）而表现出形状变化1，2，3，4。在众多刺激响应软机器人中，基于N-异丙基丙烯酰胺（NIPAM）水凝胶的软机器人使用自发形状转换5，6，7，8执行所需的任务或相互作用。通常，基于NIPAM的水凝胶表现出低临界溶液温度（LCST），并且在32°C和36°C之间的生理温度附近的水凝胶系统内发生溶胀（亲水性低于LCST）和脱胀（疏水性高于LCST）性能变化9，10。LCST尖锐临界过渡点附近的这种可逆溶胀机制可以产生基于NIPAM的水凝胶软机器人2的形状转变。因此，基于热响应NIPAM的水凝胶软机器人具有改进的操作，例如行走，抓取，爬行和传感，这在多功能机械手，医疗保健系统和智能传感器中非常重要2，3，4，11，12，13，14，15，16，17， 18，19，20，21.
在制造刺激响应软机器人时，三维（3D）打印方法已广泛使用，使用直接逐层加法工艺22。各种材料，如塑料和软水凝胶，可以用3D打印23，24打印。最近，4D打印被广泛强调为一种用于创建形状可编程软机器人25，26，27，28的创新技术。这种4D打印基于3D打印，4D打印的关键特征是3D结构可以随着时间的推移改变其形状和属性。4D打印和刺激响应水凝胶的结合提供了另一种创新途径，以创建智能3D设备，当暴露于适当的外部刺激触发器（如热，pH，光以及磁场和电场）时，这些设备会随着时间的推移而改变形状25，26，27，28.这种使用各种刺激响应水凝胶的4D打印技术的发展为形状可变形的软机器人的出现提供了机会，这些机器人具有更高的响应速度和反馈灵敏度，可以显示多功能性。
本研究描述了3D打印驱动的热响应软夹持器的创建，该夹具显示形状转换和运动。值得注意的是，所描述的特定程序可用于制造各种多功能软机器人，其整体尺寸范围从毫米到厘米长度尺度。最后，预计该协议可以应用于多个领域，包括软机器人（例如，智能执行器和运动机器人），柔性电子（例如，光电传感器和芯片实验室）和医疗保健系统（例如，药物输送胶囊，活检工具和手术设备）。
Protocol
Representative Results
Discussion
在软混合夹持器的材料选择方面，首先制备了由非刺激响应AAm基水凝胶、热响应NIPAM基水凝胶和磁响应铁凝胶组成的多响应材料体系，使软混合夹持器表现出可编程的运动和形状转换。由于其热响应溶胀-溶胀特性，基于NIPAM的水凝胶在用具有不同溶胀特性的水凝胶（例如AAm基水凝胶1）制造为双层或双条结构时表现出弯曲，折叠或起皱。此外，水凝胶可以通过嵌入氧化铁（Fe2</…
Disclosures
The authors have nothing to disclose.
Acknowledgements
作者非常感谢韩国政府（MSIT）资助的韩国国家研究基金会（NRF）资助的支持（No.2022R1F1A1074266）。
Materials
| 2-Hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone | Sigma Aldrich | 410896-50G | Irgacure 2959, photoinitiator |
| 3D WOX 2X | sindoh | n/a | 3D printer for fabricating a maze |
| Acrylamide | Sigma-Aldrich | 29-007 | ≥99% |
| Airbrush compressor | WilTec | AF18-2 | |
| Ammonium persulfate | Sigma Aldrich | A4418 | |
| Auto CAD | Autodesk | n/a | software for computer-aided-design file |
| BLX UV crosslinker | BIO-LINK | U01-133-565 | |
| Cartridge | CELLINK | CSC010300102 | |
| Digital stirring Hot Plates | Corning | 6798-420D | |
| Fluorescein O-methacrylate | Sigma Aldrich | 568864 | dye of AAm gel |
| INKREDIBLE+ bioprinter | CELLINK | n/a | |
| Iron(III) Oxide red | DUKSAN general science | I0231 | |
| Laponite RD | BYK | n/a | nanoclay |
| Microcentrifuge tube | SPL | 60615 | |
| Micro stirrer bar | Cowie | 27-00360-08 | Φ3× 0 |
| N, N, N', N'-tetramethylethylenediamine | Sigma Aldrich | T7024-100ML | |
| N, N'-methylenebisacrylamide | Sigma Aldrich | M7279 | ≥99.5% |
| N-isopropylacrylamide | Sigma-Aldrich | 415324-50G | |
| Poly(N-isopropylacrylamide) | Sigma-Aldrich | 535311 | |
| Rhodamine 6G | Sigma Aldrich | R4127 | dye of NIPAM gel |
| Slic3r software (v1.2.9) | Slic3r | n/a | open-source software to convert .stl file to gcode |
| Sodium hydroxide beads | Sigma Aldrich | S5881 | |
| Sterile high-precision conical bioprinting nozzles | CELLINK | NZ3270005001 | 22 G, 25 G |
| Syringe | Korea vaccine | K07415389 | 10 CC 21 G (1-1/4 INCH) |
| Vortex mixer | DAIHAN | DH.WVM00030 |
References
- Gracias, D. H. Stimuli responsive self-folding using thin polymer films. Current Opinion in Chemical Engineering. 2 (1), 112-119 (2013).
- Zhang, Y. S., Khademhosseini, A. Advances in engineering hydrogels. Science. 356 (6337), (2017).
- Erol, O., Pantula, A., Liu, W., Gracias, D. H. Transformer hydrogels: A review. Advanced Materials Technologies. 4 (4), 1900043 (2019).
- Liu, X., Liu, J., Lin, S., Zhao, X. Hydrogel machines. Materials Today. 36, 102-124 (2020).
- Hu, Z., Zhang, X., Li, Y. Synthesis and application of modulated polymer gels. Science. 269 (5223), 525-527 (1995).
- Klein, Y., Efrati, E., Sharon, E. Shaping of elastic sheets by prescription of non-Euclidean metrics. Science. 315 (5815), 1116-1120 (2007).
- Kim, J., Hanna, J. A., Byun, M., Santangelo, C. D., Hayward, R. C. Design responsive buckled surfaces by halftone gel lithography. Science. 335 (6073), 1201-1205 (2012).
- Breger, J. C., et al. Self-folding thermo-magnetically responsive soft microgrippers. ACS Applied Materials & Interfaces. 7 (5), 3398-3405 (2015).
- Schild, H. G. Poly (N-isopropylacrylamide): Experiment, theory and application. Progress in Polymer Science. 17 (2), 163-249 (1992).
- Ahn, S., Kasi, R. M., Kim, S. -. C., Sharma, N., Zhou, Y. Stimuli-responsive polymer gels. Soft Matter. 4, 1151-1157 (2008).
- Stuart, M. A., et al. Emerging applications of stimuli-responsive polymer materials. Nature Materials. 9, 101-113 (2010).
- Ionov, L. Biomimetic hydrogel-based actuating systems. Advanced Functional Materials. 23 (36), 4555-4570 (2013).
- Ghosh, A., et al. Stimuli-responsive soft untethered grippers for drug delivery and robotic surgery. Frontiers in Mechanical Engineering. 3, 7 (2017).
- Kirillova, A., Ionov, L. Shape-changing polymers for biomedical applications. Journal of Materials Chemistry B. 7, 1597-1624 (2019).
- Le, X., Lu, W., Zhang, J., Chen, T. Recent progress in biomimetic anisotropic hydrogel actuators. Advanced Science. 6 (5), 1801584 (2019).
- Xu, W., Gracias, D. H. Soft three-dimensional robots with hard two-dimensional materials. ACS Nano. 13 (5), 4883-4892 (2019).
- Yoon, C. K. Advances in biomimetic stimuli responsive soft grippers. Nano Convergence. 6, 20 (2019).
- Lee, Y., Song, W. J., Sun, J. Y. Hydrogel soft robotics. Materials Today Physics. 15, 100258 (2020).
- Shen, Z., Chen, F., Zhu, X., Yong, K. T., Gu, G. Stimuli-responsive functional materials for soft robotics. Journal of Materials Chemistry B. 8, 8972-8991 (2020).
- Kim, H., et al. Shape morphing smart 3D actuator materials for micro soft robot. Materials Today. 41, 243-269 (2020).
- Ding, M., et al. Multifunctional soft machines based on stimuli-responsive hydrogels: From freestanding hydrogels to smart integrated systems. Materials Today Advances. 8, 100088 (2020).
- Wang, X., Jiang, M., Zhou, Z., Gou, J., Hui, D. 3D printing of polymer matrix composites: A review and prospective. Composites Part B: Engineering. 110, 442-458 (2017).
- Bartlett, N. W., et al. A 3D-printed, functionally graded soft robot powered by combustion. Science. 349 (6244), 161-165 (2015).
- Wehner, M., et al. An integrated design and fabrication strategy for entirely soft, autonomous robots. Nature. 536, 451-455 (2016).
- Tibbits, S. 4D printing: Multi-material shape change. Architectural Design. 84 (1), 116-121 (2014).
- Gladman, A. S., Matsumoto, E. A., Nuzzo, R. G., Mahadevan, L., Lewis, J. A. Biomimetic 4D printing. Nature Materials. 15, 413-418 (2016).
- Momeni, F., Hassani, S. M., Liu, X., Ni, J. A review of 4D printing. Materials & Design. 125, 42-79 (2017).
- Ionov, L. 4D biofabrication: Materials, methods, and applications. Advanced Healthcare Materials. 7 (17), 1800412 (2018).
- Liu, J., et al. Dual-gel 4D printing of bioinspired tubes. ACS Applied Materials & Interfaces. 11 (8), 8492-8498 (2019).
- Son, H., et al. Untethered actuation of hybrid hydrogel gripper via ultrasound. ACS Macro Letters. 9 (12), 1766-1772 (2020).
- Ding, Z., Salim, A., Ziaie, B. Squeeze-film hydrogel deposition and dry micropatterning. Analytical Chemistry. 82 (8), 3377-3382 (2010).
- Ongaro, F., et al. Autonomous planning and control of soft untethered grippers in unstructured environments. Journal of Micro-Bio Robotics. 12, 45-52 (2017).
- Scheggi, S., et al. Magnetic motion control and planning of untethered soft grippers using ultrasound image feedback. 2017 IEEE International Conference on Robotics and Automation (ICRA). IEEE. , 6156-6161 (2017).
