Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity

Abstract

Hydrogels attract great attention as biomaterials as a result of their soft and wet nature, similar to that of biological tissues. Recent inventions of several tough hydrogels show their potential as structural biomaterials, such as cartilage. Any given application, however, requires a combination of mechanical properties including stiffness, strength, toughness, damping, fatigue resistance and self-healing, along with biocompatibility. This combination is rarely realized. Here, we report that polyampholytes, polymers bearing randomly dispersed cationic and anionic repeat groups, form tough and viscoelastic hydrogels with multiple mechanical properties. The randomness makes ionic bonds of a wide distribution of strength. The strong bonds serve as permanent crosslinks, imparting elasticity, whereas the weak bonds reversibly break and re-form, dissipating energy. These physical hydrogels of supramolecular structure can be tuned to change multiple mechanical properties over wide ranges by using diverse ionic combinations. This polyampholyte approach is synthetically simple and dramatically increases the choice of tough hydrogels for applications.

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Figure 1: Schematics of physical hydrogels composed of polyampholytes.
Figure 2: The effect of monomer concentration on the physical properties of polyampholytes.
Figure 3: Self-recovery, fatigue resistance, adhesion and self-healing behaviours of polyampholyte hydrogels.
Figure 4: The effect of saline solution and deformation rate on properties of polyampholyte hydrogels P(NaSS-co-MPTC) 2.1–0.525.

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Acknowledgements

This research was financially supported by a Grant-in-Aid for Scientific Research (S) (No. 124225006) from the Japan Society for the Promotion of Science (JSPS). We thank T. Narita and M. Nargis for beneficial discussion.

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T.L.S., T.K. and J.P.G. designed the experiments. T.L.S., S.K., A.B.I., M.A.H., K.S. and T.A. performed the experiments. T.L.S., T.K., T.N. and J.P.G. analysed the data. T.L.S. and J.P.G. wrote the paper.

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Correspondence to Jian Ping Gong.

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The authors declare no competing financial interests.

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Sun, T., Kurokawa, T., Kuroda, S. et al. Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity. Nature Mater 12, 932–937 (2013). https://doi.org/10.1038/nmat3713

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