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BIT makes progress in knittable hydrogel fiber for soft robots

  Recently, Zhao Yang, a special researcher and collaborator from the School of Chemistry and Chemical Engineering, Beijing Institute of Technology, has made important progress in knittable hydrogel fiber for soft robotics. The research results are titled "Large-Scale Spinning Approach to Engineering Knittable Hydrogel Fiber for Soft Robots", which was published online in ACS Nano on October 19, and the link to the paper is https://pubs.acs.org/doi/10.1021/acsnano .0c04382. Duan Xiangyu and Yu Jingyi, undergraduates from the School of Chemistry and Chemical Engineering, Beijing Institute of Technology, are the co-first authors, and Zhao Yang, a special researcher from the School of Chemistry and Chemical Engineering, Beijing Institute of Technology, is the corresponding author. Beijing Institute of Technology is the first communication institute.

  The processing and molding of functional materials is one of the difficulties in the research of new stimulus-responsive soft robots. At the same time, fiber processing and molding technology has been widely studied and applied in the textile industry. If the hydrogel fiber is processed into a soft robot, the rapid stimulus response and flexibility of the hydrogel fiber will effectively improve the performance of the soft robot. However, the current development of stimulus-responsive gel fibers faces two main difficulties: First, the compatibility of the existing hydrogel fiber production process is poor. The existing methods such as microfluidic spinning, electrospinning, melt spinning, and ink direct-writing spinning all affect the physical properties of the fiber monomer solution. The properties have additional requirements or require a fast curing process; Second, due to its high water content and poor mechanical strength, hydrogel fibers will break under low stress and cannot be processed in a complex or automated manner. Therefore, the existing reports of hydrogel weaving are limited to simple structures, and there are no reports of soft robots woven made from stimulus-responsive hydrogels.

Figure 2. Self-lubricating spinning method and hydrogel fiber characterization

  Based on this, the author of this article proposes a spinning method that uses the free movement of linear polymers during the solution polymerization of hydrogel precursors to produce a lubricating layer (self-lubricating phenomenon). And the drying and plasticizing effects of triethylene glycol are used to effectively increase the strength of the prepared fiber. The hydrogel precursor solution is composed of linear polymer poly(2-acrylamide-2-methylpropanesulfonic acid) (PAMPS) and monomer acrylamide (AAm). During the polymerization process, AAm gradually forms a three-dimensional polymer network through free radical polymerization, while PAMPS does not participate in the reaction and moves randomly in the precursor solution. Inevitably, part of PAMPS will be partially/fully discharged out of the network formed by PAAm , and it can move relatively freely. The PAMPS on the surface of this layer and solvent water molecules form a lubricating layer, which separates the hydrogel network from the container and lubricates the movement of the hydrogel network. Based on this, the researchers proposed a self-lubricating spinning process (Figure 2).

Figure 3. Characterization of electrical response and tensile strength of gel fiber

  However, the mechanical strength of this fiber is still insufficient to support further processing and application. Therefore, the author put the hydrogel fiber in the triethylene glycol to carry out solvent replacement, in this process, the water molecules in the hydrogel fiber are removed, which brings about the improvement of the mechanical strength. At the same time, a small amount of triethylene glycol enters the gel network. Compared with the simple and dry glue fiber, the gel network obtained by the substitution of triethylene glycol can maintain a certain degree of flexibility.

Figure 4. Gel fiber woven structure

  The fibers were then made into crochet flowers, woven fabrics, stacked cylinders and five-pointed stars, braids, hollow cages and other shapes using different weaving methods.

Figure 5. Gel fiber soft robot

  Finally, the author uses COMSOL finite element simulation to assist in the design of the electrode, combining the electrode with the woven structure, and creating a series of underwater bionic soft robots.

  Personal profile:

  Zhao Yang is a special researcher and doctoral supervisor of the School of Chemistry and Chemical Engineering, Beijing Institute of Technology. He has published 38 SCI papers as the first or corresponding author, including JACS, Angew.Chem.Int.Ed., Adv.Mater., Energy Environ.Sci., ACS Nano, etc. He has published a total of more than 90 SCI papers, 4 ESI highly cited papers, with more than 8,000 citations, and 4 authorized patents, of which 1 result has been industrialized. One paper won the 2012 "China's 100 Most Influential International Academic Papers". He presided over a number of National Natural Science Foundation and Beijing Natural Science Foundation projects, and participated in a number of major national basic research and development (973) projects, key research and development projects, and military pre-research projects, and was selected as an outstanding young talent of Beijing Natural Science Foundation.

  Duan Xiangyu: a 2015 undergraduate of the School of Chemistry and Chemical Engineering. From 2019 to 2020, he entered the research group of Professor Qu Liangti and carry out this research under the guidance of researcher Zhao Yang; From 2017 to 2019, he entered the research group of Professor Wang Bo of the School of Chemistry and Chemical Engineering to engage in MOF material research and published a paper in Angew.Chem.Int.Ed. as the third author; from 2015 to 2017, as the first and second eco-shop owners of the sub-management branch of entrepreneurship base for college students, he conducted certain scientific research and won 3 municipal competition awards.

  Yu Jingyi: a 2016 undergraduate of the School of Chemistry and Chemical Engineering. In 2017, she entered the research group of Professor Qu Liangti of the School of Chemistry and Chemical Engineering to carry out subjects related to cathode materials for lithium-sulfur batteries, and published a paper in Carbon as the second author; In 2019, she started to carry out the research on this subject under the guidance of researcher Zhao Yang; from 2017 to 2018, as the third eco-shop owners of the sub-management branch of entrepreneurship base for college students, she conducted certain scientific research and won 1 municipal competition award and 1 national competition award.