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Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics

Abstract

In conventional polymer materials, mechanical performance is traditionally engineered via material structure, using motifs such as polymer molecular weight, polymer branching, or block copolymer design1. Here, by means of a model system of 4-arm poly(ethylene glycol) hydrogels crosslinked with multiple, kinetically distinct dynamic metal–ligand coordinate complexes, we show that polymer materials with decoupled spatial structure and mechanical performance can be designed. By tuning the relative concentration of two types of metal–ligand crosslinks, we demonstrate control over the material’s mechanical hierarchy of energy-dissipating modes under dynamic mechanical loading, and therefore the ability to engineer a priori the viscoelastic properties of these materials by controlling the types of crosslinks rather than by modifying the polymer itself. This strategy to decouple material mechanics from structure is general and may inform the design of soft materials for use in complex mechanical environments. Three examples that demonstrate this are provided.

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Figure 1: Model materials systems with orthogonally tunable mechanical temporal hierarchy.
Figure 2: Rheological properties of single metal-ion hydrogels.
Figure 3: Hierarchical mechanics of double metal-ion coordinate networks.
Figure 4: Relative contributions of slow and fast relaxation modes in double metal-ion hydrogels.
Figure 5: The effects of temporal mechanical hierarchy in systems beyond model 4PEG-His hydrogels.

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Acknowledgements

S.C.G. was supported by the Anne M. Mayes Fellowship. S.C.G. and N.H.-A. were supported by the MRSEC programme of the National Science Foundation under award number DMR—0819762 and DMR-1419807. N.H.-A. was supported by the MIT Sea Grant via the Doherty Professorship in Ocean Utilization. D.G.B., J.C. and P.B.M. were supported by the National Institutes of Health under award number R37DE014193. D.M. and Z.G. were supported by the US Department of Energy, Division of Materials Sciences, under award number DE-FG02-04ER46162.

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S.C.G. and N.H.-A. designed the study, conducted the analysis and prepared the manuscript. S.C.G. and R.L. synthesized hydrogels and conducted experiments. D.M., Z.G., J.C., D.G.B. and P.B.M. synthesized materials and provided discussion.

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Correspondence to Niels Holten-Andersen.

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The authors declare no competing financial interests.

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Grindy, S., Learsch, R., Mozhdehi, D. et al. Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics. Nature Mater 14, 1210–1216 (2015). https://doi.org/10.1038/nmat4401

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