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Bio-inspired mechanically adaptive materials through vibration-induced crosslinking

Abstract

In nature, bone adapts to mechanical forces it experiences, strengthening itself to match the conditions placed upon it. Here we report a composite material that adapts to the mechanical environment it experiences—varying its modulus as a function of force, time and the frequency of mechanical agitation. Adaptation in the material is managed by mechanically responsive ZnO, which controls a crosslinking reaction between a thiol and an alkene within a polymer composite gel, resulting in a mechanically driven ×66 increase in modulus. As the amount of chemical energy is a function of the mechanical energy input, the material senses and adapts its modulus along the distribution of stress, resembling the bone remodelling behaviour that materials can adapt accordingly to the loading location. Such material design might find use in a wide range of applications, from adhesives to materials that interface with biological systems.

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Fig. 1: Conceptual illustration of bone remodelling and synthetic self-adaptive material via mechano-thiol–ene polymerization.
Fig. 2: Strengthening of an organo-gel via mechano-chemical crosslinking.
Fig. 3: Adaptation of the organo-gel modulus to different mechanical inputs.
Fig. 4: Remodelling of material structure and modelling of force distribution.

Data availability

Source data are provided with this paper. The other data that support the findings of this study are available within the paper and its Supplementary Information files and available from the corresponding author upon reasonable request.

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Acknowledgements

We thank M. Garg for performing the μCT imaging and S. C. W. Huang for the helpful discussion. Parts of this work were carried out at the Soft Matter Characterization Facility, the FIB-SEM facility of the University of Chicago and the SPID facility of Northwestern University’s NUANCE Center. The work was supported by AFOSR COE 5‐29168, NSF CHE‐1710116 and ARO W911NF‐17‐1‐0598 (71524‐CH). We dedicate this paper to Prof. Scott White who served as both an inspiration for this work and a personal inspiration for the authors.

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Contributions

Z.W., J.W., J.A. and A.P.E.-K. conceived the concept. Z.W., J.W. and A.P.E.-K. designed the experiments. Z.W., J.W., J.A., Z.H. and S.M. performed the experiments and analysed the data. T.S. conducted the finite element simulation. All authors participated in writing the manuscript.

Corresponding author

Correspondence to Aaron P. Esser‐Kahn.

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The authors declare no competing interests.

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Peer review information Nature Materials thanks Stephen Craig and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–14 and Tables 1–5.

Supplementary Video 1

Compression test of the control sample without mechanical activation.

Supplementary Video 2

Compression test of the organo-gel via mechano-chemical crosslinking.

Source data

Source Data Fig. 1

Molecular weight versus monomer conversion and GPC traces at different times.

Source Data Fig. 2

Stress–strain curves of the gel.

Source Data Fig. 3

Storage modulus change as a function of force, frequency and time.

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Wang, Z., Wang, J., Ayarza, J. et al. Bio-inspired mechanically adaptive materials through vibration-induced crosslinking. Nat. Mater. 20, 869–874 (2021). https://doi.org/10.1038/s41563-021-00932-5

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