Supramolecular–covalent hybrid polymers for light-activated mechanical actuation

Abstract

The development of synthetic structures that mimic mechanical actuation in living matter such as autonomous translation and shape changes remains a grand challenge for materials science. In living systems the integration of supramolecular structures and covalent polymers contributes to the responsive behaviour of membranes, muscles and tendons, among others. Here we describe hybrid light-responsive soft materials composed of peptide amphiphile supramolecular polymers chemically bonded to spiropyran-based networks that expel water in response to visible light. The supramolecular polymers form a reversibly deformable and water-draining skeleton that mechanically reinforces the hybrid and can also be aligned by printing methods. The noncovalent skeleton embedded in the network thus enables faster bending and flattening actuation of objects, as well as longer steps during the light-driven crawling motion of macroscopic films. Our work suggests that hybrid bonding polymers, which integrate supramolecular assemblies and covalent networks, offer strategies for the bottom-up design of soft matter that mimics living organisms.

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Fig. 1: Preparation of supramolecular polymer–covalent network hybrids by copolymerization.
Fig. 2: Mechanical reinforcement of hydrogels by supramolecular polymers.
Fig. 3: Simulation of photo-actuation in the hybrid materials.
Fig. 4: Bending behaviours of PA hybrid hydrogel films induced by light irradiation.
Fig. 5: Unidirectional crawling movement of a four-footed PA hybrid hydrogel.
Fig. 6: Rotational motion of a four-footed PA hybrid hydrogel crawler.

Data availability

The data that support the findings of this study are available within the article and its Supplementary Information and from the corresponding authors upon reasonable request.

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Acknowledgements

This work was supported by the Center for Bio-Inspired Energy Science (CBES), an Energy Frontiers Research Center (EFRC) funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0000989. Z.A. received postdoctoral support from the Beatriu de Pinós Fellowship 2014 BP‐A 00007 (Agència de Gestió d'Ajust Universitaris i de Recerca, AGAUR) and a Paralyzed Veterans of America (PVA) (grant no. PVA17_RF_0008). This work made use of the Peptide Synthesis Core Facility (peptide synthesis) of the Simpson Querrey Institute at Northwestern University. This facility has current support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS–1542205). The Simpson Querrey Institute, Northwestern University Office for Research, US Army Research Office, and the US Army Medical Research and Materiel Command also provided funding to develop this facility. This work also made use of the EPIC and BioCryo facilities as well as the CryoCluster equipment of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC Program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN and the MRI program (NSF DMR-1229693). This work also made use of the MatCI Facility, which receives support from the MRSEC Program (NSF DMR-1720139) of the Materials Research Center at Northwestern University. This work also made use of the IMSERC at Northwestern University, which has received support from the NIH (1S10OD012016-01/1S10RR019071-01A1), Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the State of Illinois, and the International Institute for Nanotechnology (IIN). This work also made use of Keck Biophysics Facility at Northwestern University. X-ray experiments were performed at the DuPont–Northwestern–Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, The Dow Chemical Company, and DuPont de Nemours, Inc. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. X-ray scattering data was collected using an instrument funded by the National Science Foundation under Award Number 0960140. We thank Z. Yu for helpful discussion and R. Qiu for 1H nuclear Overhauser effect spectroscopy NMR analysis. We thank M. Seniw for providing schematic illustrations.

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Authors

Contributions

C.L. designed and performed most of the experiments and wrote the manuscript. A.I. performed the CG simulations and wrote the manuscript. H.S. carried out X-ray scattering and Cryo-SEM, K.S. and S.M.C. collected Cryo-TEM, N.A.S. performed 3D printing and Z.A. collected confocal microscopy data. L.C.P., G.C.S. and S.I.S. wrote the manuscript and supervised the research.

Corresponding authors

Correspondence to George C. Schatz or Samuel I. Stupp.

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Supplementary information

Supplementary Information

Supplementary Videos 1–21 legends, methods, Figs. 1–48, Tables 1–5 and references.

Reporting Summary

Supplementary Video 1

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran with 0.5 mm thickness bends towards a top light source.

Supplementary Video 2

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran with 0.2 mm thickness bends towards a top light source.

Supplementary Video 3

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran with 1.0 mm thickness bends towards a top light source.

Supplementary Video 4

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran with 2.0 mm thickness bends towards a top light source.

Supplementary Video 5

Soft covalent polymer hydrogel (2.8% crosslinking) made of nitro-spiropyran exhibits a low degree of bending (<5°).

Supplementary Video 6

Stiff covalent polymer hydrogel (10% crosslinking) made of nitro-spiropyran exhibits a slower response to light.

Supplementary Video 7

Glass fibre (5 wt%) reinforced covalent polymer hydrogel (2.8% crosslinking) made of nitro-spiropyran exhibits a slower response to light.

Supplementary Video 8

PA (0.5 wt%) hybrid hydrogel made of nitro-spiropyran with 0.5 mm thickness bends towards a top light source.

Supplementary Video 9

PA (1.5 wt%) hybrid hydrogel made of nitro-spiropyran with 0.5 mm thickness bends towards a top light source.

Supplementary Video 10

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran (0.5 mm thickness) with aligned PA fibres made by 3D printing bends towards a top light source.

Supplementary Video 11

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran (0.5 mm thickness) with non-aligned PA fibres made by casting bends towards a top light source.

Supplementary Video 12

PA (1 wt%) hybrid hydrogel made of nitro-spiropyran walks unidirectionally on ratcheted surface with a step length of 2.2 mm.

Supplementary Video 13

Soft covalent polymer hydrogel (2.8% crosslinking) made of nitro-spiropyran walks unidirectionally on ratcheted surface with a step length of 0.5 mm.

Supplementary Video 14

PA (1 wt%) hybrid hydrogel made of spiropyran without nitro substituent walks unidirectionally on ratcheted surface with a step length of 2.6 mm.

Supplementary Video 15

Soft covalent polymer hydrogel (2.8% crosslinking) made of spiropyran without nitro substituent walks unidirectionally on ratcheted surface with a step length of 1.1 mm.

Supplementary Video 16

Five steps of unidirectional motion by the PA (1 wt%) hybrid actuator made of nitro-spiropyran after alternating periods of light on (30 min) and light off (10 h).

Supplementary Video 17

Five steps of unidirectional motion by the PA (1 wt%) hybrid actuator made of a spiropyran without nitro substituent after alternating periods of light on (20 min) and light off (1.5 h).

Supplementary Video 18

A PA (1 wt%) hybrid crawler made of nitro-spiropyran with PA fibres aligned parallel to the crawling direction gives a step length of 4.7 mm.

Supplementary Video 19

A PA (1 wt%) hybrid crawler made of nitro-spiropyran with PA fibres aligned perpendicular to the crawling direction gives a step length of 1.8 mm.

Supplementary Video 20

A PA (1 wt%) hybrid crawler made of nitro-spiropyran with PA fibres non-aligned gives a step length of 3.5 mm.

Supplementary Video 21

Rotational motion of a PA (1 wt%) hybrid hydrogel actuator made of nitro-spiropyran.

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Li, C., Iscen, A., Sai, H. et al. Supramolecular–covalent hybrid polymers for light-activated mechanical actuation. Nat. Mater. 19, 900–909 (2020). https://doi.org/10.1038/s41563-020-0707-7

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