Mechanochemical Regulated Origami with Tough Hydrogels by Ion

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Mechano-chemical regulated origami with tough hydrogels by ion transfer printing Xiaohu Zhou, Tianzhen Li, Jiahui Wang, Fan Chen, Dan Zhou, Qi Liu, Baijia Li, Jingyue Cheng, Xuechang Zhou, and Bo Zheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01610 • Publication Date (Web): 21 Feb 2018 Downloaded from http://pubs.acs.org on February 22, 2018

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ACS Applied Materials & Interfaces

Mechano-chemical regulated origami with tough hydrogels by ion transfer printing Xiaohu Zhou,1,2 Tianzhen Li,1 Jiahui Wang,1 Fan Chen,1 Dan Zhou,1 Qi Liu,2 Baijia Li,1 Jingyue Cheng,1 Xuechang Zhou1,* and Bo Zheng2,* 1

College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen

518060, P. R. China 2

Department of Chemistry, The Chinese University of Hong Kong,Shatin, N.T., Hong

Kong SAR, P. R. China

*Correspondence and requests for materials should be addressed to X. C. Z. (email: [email protected]) or B.Z. (email: [email protected]).

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT:

Stimuli-responsive hydrogels that undergo programmable shape deformation are of great importance for a wide variety of applications spanning from soft robotics and biomedical devices to tissue engineering and drug delivery. To guide the shape morphing, anisotropic elements need to be encoded into the hydrogels during the fabrication yet extremely difficult to alter afterward. This study reports a simple and reliable mechano-chemical regulation strategy to post-engineer the hydrogels by encoding structures of high stiffness locally into pre-stretched tough hydrogels through ion transfer printing with a paper cut. During the printing, trivalent ions (Fe3+) were patterned and diffused into the pre-stretched tough gels, which dramatically increased the local stiffness by forming the second trivalent ionically crosslinked network. By removing the applied stretching force, the stiff anisotropy-encoded pre-stretched tough hydrogels underwent programmable shape morphing into complex three-dimensional (3D) origami structures due to the stiffness mismatch.

KEYWORDS: tough hydrogels, stretch, transfer printing, shape-morphing, origami


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1. INTRODUCTION To survive in nature, living systems change their shapes to respond to the environmental conditions, spanning from the skeletal muscles to the plant tissues.1-4 Artificial shape-morphing materials, such as shape-memory alloys,5 piezoelectric materials,6 and soft actuators,1 typically consist of stimuli-responsive structures or elements, which can induce morphological changes or even movement when exposing to different conditions (i.e., temperatures, humidity, pH, light, etc.). In the past few years, these materials have been insensitively investigated toward a wide variety of applications,7-9

including

microelectronics,10-12

soft

robotics,13-16

sensors,17-19

actuators,20-25 light regulation devices,26-27 biomedical device,28 tissue engineering29 and drug delivery.30 To guide the shape morphing, the general strategy is the encoding of anisotropic elements,7 which can be further classified into two strategies: anisotropy encoding during or after the fabrication (post-engineering).31-38 In the first strategy, anisotropic structures are encoded directly during the fabrication process. For example, mostly reported hydrogel-based shape morphing systems are typically realized by the encoding of architectures with different cross-linked densities, which exhibit different swelling ratio when exposing to solvents.7 Efforts were intensively made in the localized control of the encoding structures of different physical properties in hydrogels in past few years by applying various state-of-the-art techniques. Lewis and coworkers reported a biomimetic 4D printing method to encode composite hydrogels architectures with different swelling behaviors, which lead to the formation of complex 3D morphologies in



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the presence of water.31 Huang et al. reported a similar method to obtain shape-morphing materials by the fine control of exposure time.32 Zhao et al. reported a frontal polymerization method to fabricate shape change materials, of which the anisotropy was generated by polymerization.33 The second strategy, however, anisotropic architectures with

different

properties

are

encoded

after

the

fabrication

or

so-called

post-engineering.34-38 Wu et al. reported a two-step photolithographic method to guide the shape transformation of the hydrogel sheet with periodic strips.35 Wang et al. reported site-specific pre-swelling-directed shape-morphing system to fabricate patterned hydrogels.36 In addition to photolithography, various chemical printing methods were applied to post-engineering the anisotropic elements to the pre-fabricated hydrogels. For example, Dicky and coworkers reported an electrically assisted ionoprinting method to reversibly actuate the hydrogels into complex structures.34 Recently, Peng et al reported the direct ion inkjet printing37 and paper-based transfer printing38 to guide the folding according to different swelling behaviors. Despite these fruitful advances, hydrogel-based shape morphing systems are still at the beginning of the development as compared with their natural analogs. For instance, most existing hydrogels are too weak and brittle for many applications that require being functioning in the presence of stress.7 These hydrogel-based shape-morphing structures are typically fragile with limited choices of applications. Tough hydrogels,39-55 one emerging type of hydrogels with ultrahigh mechanical toughness, are one of the ideal candidates for shape-morphing systems.37-38, 56-60. Tough


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hydrogels consist of single,61 double,40 or even multiple networks.62 For instance, the highly stretchable double network tough hydrogels of ionically (Ca2+) crosslinked alginate and covalently crosslinked polyacrylamide (PAAm) is one of the double network tough gels with a fracture energy as high as ~ 9000 J·m-2.42 Importantly, the strength of this double network tough gel of alginate and PAAm can be further tuned with various multivalent cations.63 With the outstanding properties of stretchability and toughness, this tough hydrogel has been successfully applied to various areas, spanning from optical fiber to biomedical devices.64-67 Recently, we reported that the Ca-alginate/PAAm tough gels could be locked by patterning of the trivalent ions Fe3+.68 The applied ferric ions would diffuse into the tough gel matrix to extremely enhance the local stiffness by forming the second ionically crosslinked network. These early attempts have shown the possibility in the development of tough hydrogel-based shape-morphing systems through the combination of state-of-the-art ion patterning technique. To advance this field, herein, we report a simple and reliable mechano-chemical regulation strategy to post-engineer the hydrogels by encoding structures of high stiffness locally into pre-stretched tough hydrogels through ion transfer printing with a paper cut. In this method, tough gels were mechanically pre-stretched to a certain stretch ratio, and then the paper-cut with the programmed pattern was put on the gel surface for chemical patterning by ion transfer printing. This paper cut was pre-dyed with the ferric solution and maintained with proper wetness before the transfer printing. During the printing, trivalent ions were patterned and diffused into the pre-stretched tough gel, which



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dramatically increased the local stiffness by forming the second trivalent ionically crosslinked

network.

By

removing

the

applied

stretching

force,

the

stiff

anisotropy-encoded pre-stretched tough hydrogels underwent programmable shape morphing into complex three-dimensional (3D) origami structures due to the stiffness mismatch. To the best of our knowledge, it is the first time to report the mechano-chemical regulation with ion transfer printing to create tough gel origami structures. Compared to the existing method for hydrogel-based shape-morphing systems, there are three important features of our mechano-chemical regulation strategy. First, no solvent is required. The common strategy for hydrogel-based shape-morphing is caused by the uneven swelling/deswelling of the different part of a gel sample,7-8 which requires the gel immersion in the proper solvent (e.g. water for swelling, and ethanol for deswelling). Our method is based on the stiffness mismatch of the locked and unlocked parts of the pre-stretched tough gel. Second, the ion transfer printing with filter paper cut is convenient and versatile, and various patterns could be easily transferred to the tough gel, hence forming various origami structures. Finally, extremely high bending angle (more than 1800 degree) can be achieved through appropriate mechano-chemical regulation due to the highly stretchable tough gel. 2. EXPERIMENTAL SECTION: 2.1 Materials: Sodium alginate was purchased from Aladdin. Acrylamide and ammonium persulfate (APS) and calcium sulfate dihydrate (CaSO4·2H2O) were purchased

from

Macklin.

N,N’-methylenebisacrylamide


(MBAA)

and

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N,N,N’,N’-tetramethylethylenediamine (TEMED) were purchased from Sigma-Aldrich. Ferric chloride hexahydrate (FeCl3·6H2O) was purchased from Fisher chemical. Advantec No.2 filter paper was used for ion transfer printing. 2.2 Synthesis of Ca-alginate/PAAmtough hydrogels: Sodium alginate (0.25 g) and acrylamide (2.00 g) were dissolved in 12.5 mL deionized water. After degassing for 2 hours, 60 µL0.10 g/mL APS aqueous solution as photo-thermal-initiator, 96µL 0.025 g/mL MBAA aqueous solution as crosslinking agent, and 10 µL TEMED as crosslinking accelerator were added to the former solution. Subsequently, 4 mL calcium sulfate (CaSO4·2H2O, 0.0221 g) aqueous slurry was added as anionic crosslinker for alginate. The resulting solution was poured into a plastic container and cured with UV light at a wavelength of 254 nm (25 W, ZF-5, Shanghai Jiapeng) at 55 oC for 1.5 h. Subsequently, the cured mixture was left in a humid box for several hours to stabilize the reactions. 2.3 Mechanically stretching: The as-prepared tough gels were cut into strips (length: ~ 24 mm, width: ~ 2 mm). The tough gel strip was clamped at both ends (~ 2 mm) by the binder clips before stretch. Then, the gel strip was mechanically stretched to certain times its initial length and hold at the optical table for ion transfer printing. 2.4 Ion transfer printing with paper-cut: To obtain the best bending efficiency, 1 M ferric chloride solution was used. Filter papers cut into different patterns were first immersed in the ferric solution for dyeing for seconds, then the towel tissue was placed on the paper slightly to absorb the free water in the paper. After depleted the free water,



the transfer paper dyed with ferric ions could be put on the tough gel for transfer printing immediately. 2.5 Penetration depth and bending angle measurements: The patterned gels were observed under the microscope (Leica MZ 16, Germany) equipped with a CCD camera (SPOT Insight, Diagnostic Instruments). The penetration depths and bending angles of the gel were measured with the photographs by ImageJ (NIH). As the ferric ion patterned part of the gel was brown, we measured the penetration depth by color analysis. Because the ferric ion concentration in the gel was continuously and dynamically changing due to diffusion, and the boundary of the patterned and unpatterned parts was not sharp, the penetration depth was roughly measured. 2.6 Energy-Dispersive X-ray Spectroscopy (EDS) investigation: Patterned tough gel samples were plunged into liquid nitrogen for about 5 min, and then freeze-dried in a vacuum freeze-dryer (SCIENTZ-12N, Ningbo Scientz Biotechnology Co. Ltd) for about 20 h to remove water. The ferric ion distribution analysis was performed with the energy-dispersive X-ray spectrometer (Oxford instrument) attached to the scanning electron microscopy (SEM) (JSM-7800F, JEOL, Japan). The gel samples would have some shrinkage during the freeze-drying, and the locked and unlocked part had a little (~10%) different in shrinkage ratio, which would cause the sample surface uneven. The uneven surface of the sample would generate some unusual peaks. 3. RESULTS AND DISCUSSION:


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3.1 Mechano-chemical regulated origami bending Normally, as the tough gel is mechanically stretched without fracture, the strain energy will be stored in the gel by the stretching. The tough gel will shrink back to its initial shape with the stored strain energy upon release, due to the high stretchability and toughness.42 However, when ferric ions are asymmetrically printed in the pre-stretched tough gel to partially lock the gel, the locked part of the gel will only shrink very little for the high stiffness (Supplementary Fig.S1).68 Therefore, this shrinkage mismatch of the ferric ion patterned (locked) and the unpatterned (unlocked) pre-stretched tough gel will induce the folding and bending of the stretched tough gel (Fig. 1). For simple qualitative analysis, the stored strain energy density (u) is positively related to the stretch ratio (λ). The larger stretch will generate higher stored strain energy density. The stored strain energy (U) is the product of the strain energy density and the volume (V).69 Since the Ca-alginate/PAAm gel has high toughness, the stored strain energy is high, and the folding and bending force is large. However, not all the stored strain energy would be used for the origami bending, while only the strain energy stored by the unlocked part of the asymmetric patterned areas would contribute to the bending (Fig. 1c). The unlocked part would like to shrink back while the locked part was resistant to shrinkage. This competition between the locked and the unlocked parts would induce the bending. The unpatterned areas would not be affected, which would shrink back to the initial shape when the gel was released (Fig. 1c).



For a simple analysis, the asymmetric patterned area could be viewed as layer concept, though the concentration of the ferric ions in the gel matrix was continuously and dynamically changing due to diffusion. Therefore, the effective strain energy (Ue) for the origami bending depends on the strain energy density (u) and the volume of the unlocked part (Vu). The strain energy density (u) is the function of the stretch ratio (λ): = (), while the volume of the unlocked part (Vu) depends on the pattern length (l) and the thickness of the unlocked part (du). Therefore, we have the following relationship: ≈ ∙ ~ ∙ ∙ (). Given a constant thickness of the tough hydrogels, the bending angle of the tough gel is determined by varying the length (l) and the thickness (d) of chemical patterning with the constant stretch ratio (λ). As shown in Fig. 1d, with the same thickness of the unlocked part (α,β), the longer patterned part has the larger bending angle (β>α), while with the same patterned length (α, γ), the thicker unlocked part has the larger bending angle (γ>α). Note that the transferred ferric ions would continuously diffuse in the tough gel matrix until it reached the equilibrium in concentration, but the bending angle would not change after the bending structure formed because the strain energy has already been released. To reduce the effect of the internal damage after each loading,42 all the bending experiments in this work were done within the first 2 loadings.


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Figure 1. The schematic illustration of the mechano-chemical strategy to create origami structures. The tough hydrogel (a) was first mechanically stretched, then the chemical patterning was applied by the ion transfer printing with paper-cuts (b). The patterned Fe3+ ions could extremely enhance the local stiffness of the tough gel. (c, d) The bending angles of the tough gel were controlled by the patterning lengths (l) and ion penetration depths (d).

3.2 Ion transfer printing with paper-cut



Owing to the easiness to adjust the deformation level and transfer large complex patterns, the convenient and versatile paper transfer printing method was used to pattern the tough gel surface with the ferric ions to create origami structures.38Filter papers with various patterns by cutting were first dip-dying with a ferric solution, then they were put on the tough gel for ion transfer printing (Fig. 2a). The ion penetration velocity in the gel was related to the wetness (the amount of water) of the transfer paper. If the transfer paper contained more water, the ion penetration velocity was faster due to the faster swelling of the tough gel. However, it is difficult to maintain a consistent wetness of the papers when they contain some free water. To precisely control the ion penetration depth, the wetness of the filter paper for the transfer printing should be well controlled and kept consistent. The transfer paper was first immersed in the ferric solution for dying for a few seconds, then the towel tissue was placed on the transfer paper to absorb the free water from the paper surface. After removing the free water, we immediately placed the transfer paper dyed with ferric ions on the tough gel for transfer printing. With this method, we could precisely control the ion penetration depth by controlling the transfer time (Fig. 2b and 2c). To create bending and origami structures, the tough gels should be pre-stretched to a certain stretch ratio. We also showed that the penetration depth was independent of the stretch ratio of the tough gel (Fig. 2b and 2c), though the thickness of the gel would decrease as the gel was stretched (Supplementary Fig. S2). Because the thickness of the unlocked part (du) was


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controlled by the penetration depth, we could precisely control the bending force with this ion transfer printing. We also investigated the concentration distribution of the ferric ion in the tough gel with the EDS experiments. The results confirmed that the concentration of the ferric ion in the gel was continuously and decreased from the transfer printing side to the other side (Supplementary Fig. S3). The thickness of ferric layer showed good consistency with our measurements with optical microscope.



Figure 2. Ion transfer printing with filter paper-cut. a) The process of the ion transfer printing with filter paper-cut. b) The process of the mechano-chemical regulation to create bending structures. The tough gel was stretched to 2 times its original length, then the paper-cuts with ferric ions were put on the stretched gel surface for transfer printing at different transfer time. Upon release, the mechano-chemical regulated gel would bend with different angles immediately. c) The penetration depth could be controlled by the ion transfer printing time. The penetration velocity was independent of the stretch of the tough gel.

3.3 Controlled bending angles According to the previous analysis, the bending angle of the mechano-chemical regulated tough gel was dependent on the volume ratio of the locked and unlocked parts at a certain stretch (Fig. 1). For the simple bending model of the gel strip with the constant thickness, the bending angle was controlled by the ion patterning length (l) and thickness (d). Since we could control the penetration ratio with the ion transfer printing method, we could control the bending angle of the tough gel. Firstly, we used the 10 mm paper strips to transfer the ferric ions with different penetration ratios, and the tough gels were pre-stretched to 2 times its initial length. As the penetration ratio increased, the bending angle decreased (Fig. 3a and 3c). Then, we used the paper strips with different length (from 5 to 40 mm) for ion transfer printing, while kept the penetration ratio at the same (~ 0.6). The tough gels were still pre-stretched to 2 times. The results showed that


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the longer patterns, or more specifically the larger ratio of the patterning length to the thickness of the gel, would induce the larger bending angles (Fig. 3b and 3d). More interestingly, we also could find that though the bending angle increased with the patterning length increased, the bending curvature did not change much (~ 8 mm-1), because of the same ferric penetration ratio. These results show that the local bending curvature of the gel was determined by the local ferric penetration ratio, while the bending angle of the whole gel strip was controlled by the both of the ferric penetration ratio and the patterning length.

Figure 3. Bending angles were controlled by the patterning length and ion penetration ratio. a) and c) Bending angle decreased as the ion penetration ratio increased. The



thickness of the tough gel strips was 3.0 mm and 3.9 mm. b) and d) Bending angle increased as the ratio of the chemical patterning length to the gel thickness increased.

According to the analysis, the bending angle was also dependent on the stretch ratio of the tough gel. We mechanically stretched the tough gel to 2 to 10 times its original length and locked half of the stretched gel. The results showed that the larger stretch would induce the larger bending (Fig. 4).

Figure 4 a) Plot of bending angles versus the stretching ratio (λ). b) Digital images of the folded structure of tough hydrogels at different stretching ratio.

3.4 Origami structures


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Structures presented in the previous section were simple bending structures with one single side. In this section, we show that the complex origami structures could be created with the mechano-chemical regulation strategy (Fig. 5). The helix structures and the Chinese Ding-like structure were created by patterning the stretched gel sheets with one side (Fig. 5a and 5b), while the saddle structure was created by orthogonally patterning the gel with two-side (Fig. 5c). We also showed that our method could create kirigami structure (Fig. 5d). The tough gel sheet was first orthogonally stretched, then the flower pattern was transferred to the gel surface for two minutes. We would get the flower structure by cutting off the unpatterned areas (Fig. 5d).

Figure 5. Fabrication of various origami structures. a) Helix structures with uniaxially stretched gel sheets. b) Chinese Ding-like structure with biaxially stretched gel sheet. c)



Saddle surface structure by orthogonally patterning two-side of the biaxially stretched gel sheet. d) Flower kirigami structure by stretching, patterning, and cutting.

4. CONCLUSIONS We presented a mechano-chemical regulation strategy to create the 3D origami structures with the ion transfer printing method. The origami bending process is based on the stiffness mismatch of the locked (Fe3+) and unlocked (Ca2+) pre-stretched tough gel. When the ferric ions were asymmetrically applied to the stretched tough gel, they would form the second ionically crosslinked network to extremely enhance the local stiffness. Upon releasing the tough gel, the unlocked part would like to shrink back with the stored strain energy, while the locked part was resistant to shrink. This competition between the locked and the unlocked parts would induce the bending. We also showed that the ion transfer printing could precisely control the pattern length and ion penetration depth, accordingly control the bending angle of the gel. Various origami/kirigami structures could be created with these methods. These methods provide a novel and simple route for creating origami-based metamaterials, and we expect them to have broad applications in biomedical devices and soft robots.

ASSOCIATED CONTENT Supporting Information


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The Supporting Information is available free of charge on the ACS Publications website. Images showing the shrinkage difference between the locked and unlocked tough gel strips, plot of the thickness versus the stretch, plot of the ferric ion penetration ratio versus the transfer time, SEM-EDS profiles of the concentration distribution of the ferric ion in the gel (pdf).

AUTHOR CONTRIBUTIONS

X. H. Z. and X. C. Z. designed the project. T. Z. L., J. H. W., F. C., D. Z.,B. J. L. and J. Y. C. fabricated the tough gel. X. H. Z. and Q. L. performed the experiments. X. H. Z. analyzed the data. X. H. Z., X. C. Z. and B. Z. wrote the manuscript. X. C. Z. and B. Z. supervised the study. All authors commented on the paper.

ACKNOWLEDGEMENTS

We acknowledge the National Natural Science Foundation of China (21674064), Shenzhen Science and Technology Foundation (JCYJ20160520173802186), the Natural Science Foundation of SZU (827-000040), and Research Grants Council of Hong Kong (B. Z., GRF14302315).

REFERENCES



(1) Oliver, K.; Seddon, A.; Trask, R. S., Morphing in Nature and Beyond: A Review of Natural and Synthetic Shape-Changing Materials and Mechanisms. J. Mater. Sci. 2016, 51, 10663-10689. (2) White, T. J.; Broer, D. J., Programmable and Adaptive Mechanics with Liquid Crystal Polymer Networks and Elastomers. Nat. Mater. 2015, 14, 1087-1098. (3) Noblin, X.; Rojas, N. O.; Westbrook, J.; Llorens, C.; Argentina, M.; Dumais, J., The Fern Sporangium: A Unique Catapult. Science 2012, 335, 1322-1322. (4) Forterre, Y.; Skotheim, J. M.; Dumais, J.; Mahadevan, L., How the Venus Flytrap Snaps. Nature 2005, 433, 421-425. (5) Jani, J. M.; Leary, M.; Subic, A.; Gibson, M. A., A Review of Shape Memory Alloy Research, Applications and Opportunities. Mater. Des. 2014, 56, 1078-1113. (6) Irschik, H., A Review on Static and Dynamic Shape Control of Structures by Piezoelectric Actuation. Eng. Struct. 2002, 24, 5-11. (7) Jeon, S.-J.; Hauser, A. W.; Hayward, R. C., Shape-Morphing Materials from Stimuli-Responsive Hydrogel Hybrids. Acc. Chem. Res. 2017, 50, 161-169. (8) Liu, Y.; Genzer, J.; Dickey, M. D., "2D or Not 2D": Shape-Programming Polymer Sheets. Prog. Polym. Sci. 2016, 52, 79-106. (9) Zhang, Y. H.; Zhang, F.; Yan, Z.; Ma, Q.; Li, X. L.; Huang, Y. G.; Rogers, J. A., Printing, Folding and Assembly Methods for Forming 3D Mesostructures in Advanced Materials. Nat. Rev. Mater. 2017, 2, 17019. (10) Rogers, J.; Huang, Y. G.; Schmidt, O. G.; Gracias, D. H., Origami MEMS and NEMS. MRS Bull. 2016, 41, 123-129. (11) Du, X. M.; Cui, H. Q.; Sun, B.; Wang, J.; Zhao, Q. L.; Xia, K.; Wu, T. Z.; Humayun, M. S., Photothermally Triggered Shape-Adaptable 3D Flexible Electronics. Adv. Mater. Technol. 2017, 2, 1700120. (12) Liang, S. Q.; Li, Y. Y.; Chen, Y. Z.; Yang, J. B.; Zhu, T. P.; Zhu, D. Y.; He, C. X.; Liu, Y. Z.; Handschuh-Wang, S.; Zhou, X. C., Liquid Metal Sponges for Mechanically Durable, All-Soft, Electrical Conductors. J. Mater. Chem. C 2017, 5, 1586-1590. (13) Felton, S.; Tolley, M.; Demaine, E.; Rus, D.; Wood, R., A Method for Building Self-Folding Machines. Science 2014, 345, 644-646. (14) Ilievski, F.; Mazzeo, A. D.; Shepherd, R. E.; Chen, X.; Whitesides, G. M., Soft Robotics for Chemists. Angew. Chem. Int. Ed. 2011, 50, 1890-1895. (15) Rus, D.; Tolley, M. T., Design, Fabrication and Control of Soft Robots. Nature 2015, 521, 467-475. (16) Wehner, M.; Truby, R. L.; Fitzgerald, D. J.; Mosadegh, B.; Whitesides, G. M.; Lewis, J. A.; Wood, R. J., An Integrated Design and Fabrication Strategy for Entirely Soft, Autonomous Robots. Nature 2016, 536, 451-455. (17) Liu, Y. J.; Cao, W. T.; Ma, M. G.; Wan, P. B., Ultrasensitive Wearable Soft Strain Sensors of Conductive, Self-Healing, and Elastic Hydrogels with Synergistic "Soft and Hard" Hybrid Networks. ACS Appl. Mater. Interfaces 2017, 9, 25559-25570.


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(18) Liao, M. H.; Wan, P. B.; Wen, J. G.; Gong, M.; Wu, X. X.; Wang, Y. G.; Shi, R.; Zhang, L. Q., Wearable, Healable, and Adhesive Epidermal Sensors Assembled from Mussel-Inspired Conductive Hybrid Hydrogel Framework. Adv. Funct. Mater. 2017, 27, 1703852. (19) Tee, B. C. K.; Chortos, A.; Berndt, A.; Nguyen, A. K.; Tom, A.; McGuire, A.; Lin, Z. L. C.; Tien, K.; Bae, W. G.; Wang, H. L.; Mei, P.; Chou, H. H.; Cui, B. X.; Deisseroth, K.; Ng, T. N.; Bao, Z. N., A Skin-Inspired Organic Digital Mechanoreceptor. Science 2015, 350, 313-316. (20) Zhang, L. D.; Chizhik, S.; Wen, Y. Z.; Naumov, P., Directed Motility of Hygroresponsive Biomimetic Actuators. Adv. Funct. Mater. 2016, 26, 1040-1053. (21) Zhang, L. D.; Naumov, P., Light- and Humidity-Induced Motion of an Acidochromic Film. Angew. Chem. Int. Ed. 2015, 54, 8642-8647. (22) Zhang, L. D.; Liang, H. R.; Jacob, J.; Naumov, P., Photogated Humidity-Driven Motility. Nat. Commun. 2015, 6, 7429. (23) Zhang, L. D.; Naumov, P.; Du, X. M.; Hu, Z. G.; Wang, J., Vapomechanically Responsive Motion of Microchannel-Programmed Actuators. Adv. Mater. 2017, 29, 1702231. (24) Hu, Y.; Li, Z.; Lan, T.; Chen, W., Photoactuators for Direct Optical-to-Mechanical Energy Conversion: From Nanocomponent Assembly to Macroscopic Deformation. Adv. Mater. 2016, 28, 10548-10556. (25) Ma, M. M.; Guo, L.; Anderson, D. G.; Langer, R., Bio-Inspired Polymer Composite Actuator and Generator Driven by Water Gradients. Science 2013, 339, 186-189. (26) Liu, M. J.; Ishida, Y.; Ebina, Y.; Sasaki, T.; Aida, T., Photolatently Modulable Hydrogels Using Unilamellar Titania Nanosheets as Photocatalytic Crosslinkers. Nat. Commun. 2013, 4, 2029. (27) Liu, Y.; Shaw, B.; Dickey, M. D.; Genzer, J., Sequential Self-Folding of Polymer Sheets. Sci. Adv. 2017, 3, e1602417. (28) Randall, C. L.; Gultepe, E.; Gracias, D. H., Self-Folding Devices and Materials for Biomedical Applications. Trends Biotechnol 2012, 30, 138-146. (29) Kim, S. H.; Lee, H. R.; Yu, S. J.; Han, M. E.; Lee, D. Y.; Kim, S. Y.; Ahn, H. J.; Han, M. J.; Lee, T. I.; Kim, T. S.; Kwon, S. K.; Im, S. G.; Hwang, N. S., Hydrogel-Laden Paper Scaffold System for Origami-Based Tissue Engineering. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 15426-15431. (30) Fernandes, R.; Gracias, D. H., Self-Folding Polymeric Containers for Encapsulation and Delivery of Drugs. Adv. Drug. Del. Rev. 2012, 64, 1579-1589. (31) Gladman, A. S.; Matsumoto, E. A.; Nuzzo, R. G.; Mahadevan, L.; Lewis, J. A., Biomimetic 4D Printing. Nat. Mater. 2016, 15, 413-418. (32) Huang, L.; Jiang, R.; Wu, J.; Song, J.; Bai, H.; Li, B.; Zhao, Q.; Xie, T., Ultrafast Digital Printing toward 4D Shape Changing Materials. Adv. Mater. 2017, 29, 1605390. (33) Zhao, Z.; Wu, J. T.; Mu, X. M.; Chen, H. S.; Qi, H. J.; Fang, D. N., Origami by Frontal Photopolymerization. Sci. Adv. 2017, 3, e1602326.



(34) Palleau, E.; Morales, D.; Dickey, M. D.; Velev, O. D., Reversible Patterning and Actuation of Hydrogels by Electrically Assisted Ionoprinting. Nat. Commun. 2013, 4, 2257. (35) Wu, Z. L.; Moshe, M.; Greener, J.; Therien-Aubin, H.; Nie, Z. H.; Sharon, E.; Kumacheva, E., Three-Dimensional Shape Transformations of Hydrogel Sheets Induced by Small-Scale Modulation of Internal Stresses. Nat. Commun. 2013, 4, 1586. (36) Wang, Z. J.; Hong, W.; Wu, Z. L.; Zheng, Q., Site-Specific Pre-Swelling-Directed Morphing Structures of Patterned Hydrogels. Angew. Chem. Int. Ed. 2017, 56, 15974-15978. (37) Peng, X.; Liu, T. Q.; Zhang, Q.; Shang, C.; Bai, Q. W.; Wang, H. L., Surface Patterning of Hydrogels for Programmable and Complex Shape Deformations by Ion Inkjet Printing. Adv. Funct. Mater. 2017, 27, 1701962. (38) Peng, X.; Li, Y.; Zhang, Q.; Shang, C.; Bai, Q. W.; Wang, H. L., Tough Hydrogels with Programmable and Complex Shape Deformations by Ion Dip-Dyeing and Transfer Printing. Adv. Funct. Mater. 2016, 26, 4491-4500. (39) Zhao, X. H., Multi-Scale Multi-Mechanism Design of Tough Hydrogels: Building Dissipation into Stretchy Networks. Soft Matter 2014, 10, 672-687. (40) Chen, Q.; Chen, H.; Zhu, L.; Zheng, J., Engineering of Tough Double Network Hydrogels. Macromol. Chem. Phys. 2016, 217, 1022-1036. (41) Gong, J. P.; Katsuyama, Y.; Kurokawa, T.; Osada, Y., Double-Network Hydrogels with Extremely High Mechanical Strength. Adv. Mater. 2003, 15, 1155-1158. (42) Sun, J. Y.; Zhao, X. H.; Illeperuma, W. R. K.; Chaudhuri, O.; Oh, K. H.; Mooney, D. J.; Vlassak, J. J.; Suo, Z. G., Highly Stretchable and Tough Hydrogels. Nature 2012, 489, 133-136. (43) Chen, Q.; Zhu, L.; Zhao, C.; Wang, Q. M.; Zheng, J., A Robust, One-Pot Synthesis of Highly Mechanical and Recoverable Double Network Hydrogels Using Thermoreversible Sol-Gel Polysaccharide. Adv. Mater. 2013, 25, 4171-4176. (44) Nakajima, T.; Sato, H.; Zhao, Y.; Kawahara, S.; Kurokawa, T.; Sugahara, K.; Gong, J. P., A Universal Molecular Stent Method to Toughen Any Hydrogels Based on Double Network Concept. Adv. Funct. Mater. 2012, 22, 4426-4432. (45) Luo, F.; Sun, T. L.; Nakajima, T.; Kurokawa, T.; Zhao, Y.; Sato, K.; Bin Ihsan, A.; Li, X. F.; Guo, H. L.; Gong, J. P., Oppositely Charged Polyelectrolytes Form Tough, Self-Healing, and Rebuildable Hydrogels. Adv. Mater. 2015, 27, 2722-2727. (46) Haraguchi, K.; Takehisa, T., Nanocomposite Hydrogels: A Unique Organic-Inorganic Network Structure with Extraordinary Mechanical, Optical, and Swelling/De-Swelling Properties. Adv. Mater. 2002, 14, 1120-1124. (47) Shi, F. K.; Wang, X. P.; Guo, R. H.; Zhong, M.; Xie, X. M., Highly Stretchable and Super Tough Nanocomposite Physical Hydrogels Facilitated by the Coupling of Intermolecular Hydrogen Bonds and Analogous Chemical Crosslinking of Nanoparticles. J. Mater. Chem. B 2015, 3, 1187-1192.


Page 22 of 25

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(48) Lin, P.; Ma, S. H.; Wang, X. L.; Zhou, F., Molecularly Engineered Dual-Crosslinked Hydrogel with Ultrahigh Mechanical Strength, Toughness, and Good Self-Recovery. Adv. Mater. 2015, 27, 2054-2059. (49) Yang, Y. Y.; Wang, X.; Yang, F.; Shen, H.; Wu, D. C., A Universal Soaking Strategy to Convert Composite Hydrogels into Extremely Tough and Rapidly Recoverable Double-Network Hydrogels. Adv. Mater. 2016, 28, 7178-7184. (50) Lin, P.; Zhang, T. T.; Wang, X. L.; Yu, B.; Zhou, F., Freezing Molecular Orientation under Stretch for High Mechanical Strength but Anisotropic Hydrogels. Small 2016, 12, 4386-4392. (51) Zheng, S. Y.; Ding, H. Y.; Qian, J.; Yin, J.; Wu, Z. L.; Song, Y. H.; Zheng, Q., Metal-Coordination Complexes Mediated Physical Hydrogels with High Toughness, Stick-Slip Tearing Behavior, and Good Processability. Macromolecules 2016, 49, 9637-9646. (52) Zhu, F. B.; Cheng, L. B.; Yin, J.; Wu, Z. L.; Qian, J.; Fu, J. Z.; Zheng, Q., 3D Printing of Ultratough Polyion Complex Hydrogels. ACS Appl. Mater. Interfaces 2016, 8, 31304-31310. (53) Wu, Z. L.; Kurokawa, T.; Sawada, D.; Hu, J.; Furukawa, H.; Gong, J. P., Anisotropic Hydrogel from Complexation-Driven Reorientation of Semirigid Polyanion at Ca2+ Diffusion Flux Front. Macromolecules 2011, 44, 3535-3541. (54) Hu, J.; Hiwatashi, K.; Kurokawa, T.; Liang, S. M.; Wu, Z. L.; Gong, J. P., Microgel-Reinforced Hydrogel Films with High Mechanical Strength and Their Visible Mesoscale Fracture Structure. Macromolecules 2011, 44, 7775-7781. (55) Okumura, Y.; Ito, K., The Polyrotaxane Gel: A Topological Gel by Figure-of-Eight Cross-Links. Adv. Mater. 2001, 13, 485-487. (56) Peng, X.; Liu, T. Q.; Jiao, C.; Wu, Y. Q.; Chen, N.; Wang, H. L., Complex Shape Deformations of Homogeneous Poly(N-isopropylacrylamide)/Graphene Oxide Hydrogels Programmed by Local NIR Irradiation. J. Mater. Chem. B 2017, 5, 7997-8003. (57) Zheng, W. J.; An, N.; Yang, J. H.; Zhou, J. X.; Chen, Y. M., Tough Al-Alginate/Poly(N-isopropylacrylamide) Hydrogel with Tunable LCST for Soft Robotics. ACS Appl. Mater. Interfaces 2015, 7, 1758-1764. (58) Huang, J. H.; Zhao, L.; Wang, T.; Sun, W. X.; Tong, Z., NIR-Triggered Rapid Shape Memory PAM-GO-Gelatin Hydrogels with High Mechanical Strength. ACS Appl. Mater. Interfaces 2016, 8, 12384-12392. (59) Wu, S. P.; Yu, F.; Dong, H.; Cao, X. D., A Hydrogel Actuator with Flexible Folding Deformation and Shape Programming Via Using Sodium Carboxymethyl Cellulose and Acrylic Acid. Carbohydr. Polym. 2017, 173, 526-534. (60) Guo, M. Y.; Pitet, L. M.; Wyss, H. M.; Vos, M.; Dankers, P. Y. W.; Meijer, E. W., Tough Stimuli-Responsive Supramolecular Hydrogels with Hydrogen-Bonding Network Junctions. J. Am. Chem. Soc. 2014, 136, 6969-6977.



(61) Brown, A. E. X.; Litvinov, R. I.; Discher, D. E.; Purohit, P. K.; Weisel, J. W., Multiscale Mechanics of Fibrin Polymer: Gel Stretching with Protein Unfolding and Loss of Water. Science 2009, 325, 741-744. (62) Es-haghi, S. S.; Weiss, R. A., Fabrication of Tough Hydrogels from Chemically Cross-Linked Multiple Neutral Networks. Macromolecules 2016, 49, 8980-8987. (63) Yang, C. H.; Wang, M. X.; Haider, H.; Yang, J. H.; Sun, J. Y.; Chen, Y. M.; Zhou, J. X.; Suo, Z. G., Strengthening Alginate/Polyacrylamide Hydrogels Using Various Multivalent Cations ACS Appl. Mater. Interfaces 2013, 5, 10418-10422. (64) Guo, J. J.; Liu, X. Y.; Jiang, N.; Yetisen, A. K.; Yuk, H.; Yang, C. X.; Khademhosseini, A.; Zhao, X. H.; Yun, S. H., Highly Stretchable, Strain Sensing Hydrogel Optical Fibers. Adv. Mater. 2016, 28, 10244-10249. (65) Lin, S. T.; Yuk, H.; Zhang, T.; Parada, G. A.; Koo, H.; Yu, C. J.; Zhao, X. H., Stretchable Hydrogel Electronics and Devices. Adv. Mater. 2016, 28, 4497-4505. (66) Liu, X. Y.; Tang, T. C.; Tham, E.; Yuk, H.; Lin, S. T.; Lu, T. K.; Zhao, X. H., Stretchable Living Materials and Devices with Hydrogel-Elastomer Hybrids Hosting Programmed Cells. Proc. Natl. Acad. Sci. U.S.A. 2017, 114, 2200-2205. (67) Yuk, H.; Zhang, T.; Parada, G. A.; Liu, X. Y.; Zhao, X. H., Skin-Inspired Hydrogel-Elastomer Hybrids with Robust Interfaces and Functional Microstructures. Nat. Commun. 2016, 7, 12028. (68) Li, T. Z.; Wang, J. H.; Zhang, L. Y.; Yang, J. B.; Yang, M. Y.; Zhu, D. Y.; Zhou, X. H.; Handschuh-Wang, S.; Liu, Y. Z.; Zhou, X. C., "Freezing'', Morphing, and Folding of Stretchy Tough Hydrogels. J. Mater. Chem. B 2017, 5, 5726-5732. (69) Sadd, M. H., Elasticity: Theory, Applications, and Numerics, 2nd Edition. 2009.


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