An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets


Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings1,2. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression3,4. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets5 embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion6 and thereby induces a quasi-crystalline structural ordering7,8 over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel9,10 using light-triggered in situ vinyl polymerization11. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux12,13,14,15,16,17,18,19, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Negatively charged unilamellar metal-oxide nanosheets of titanate (TiNS) and niobate (NbNS).
Figure 2: Magnetic responses of the unilamellar metal-oxide nanosheets TiNS and NbNS.
Figure 3: Structural and optical anisotropic features of hydrogels containing cofacially oriented TiNSs in a quasi-crystalline order.
Figure 4: Mechanical anisotropy of hydrogels containing cofacially oriented TiNSs in a quasi-crystalline order.


  1. 1

    Hull, J. R. Superconducting bearings. Supercond. Sci. Technol. 13, R1–R15 (2000)

    CAS  Article  ADS  Google Scholar 

  2. 2

    Rhim, W. K. et al. An electrostatic levitator for high-temperature containerless materials processing in 1-G. Rev. Sci. Instrum. 64, 2961–2970 (1993)

    CAS  Article  ADS  Google Scholar 

  3. 3

    Scott, J. E. Elasticity in extracellular matrix ‘shape modules’ of tendon, cartilage, etc. A sliding proteoglycan-filament model. J. Physiol. 553, 335–343 (2003)

    CAS  Article  Google Scholar 

  4. 4

    Dean, D., Han, L., Grodzinsky, A. J. & Ortiz, C. Compressive nanomechanics of opposing aggrecan macromolecules. J. Biomech. 39, 2555–2565 (2006)

    Article  Google Scholar 

  5. 5

    Sasaki, T., Watanabe, M., Hashizume, H., Yamada, H. & Nakazawa, H. Macromolecule-like aspects for a colloidal suspension of an exfoliated titanate. Pairwise association of nanosheets and dynamic reassembling process initiated from it. J. Am. Chem. Soc. 118, 8329–8335 (1996)

    CAS  Article  Google Scholar 

  6. 6

    Anandarajah, A. & Ning, L. Numerical study of the electrical double-layer repulsion between nonparallel clay particles of finite length. Int. J. Numer. Analyt. Meth. Geomech. 15, 683–703 (1991)

    Article  Google Scholar 

  7. 7

    Cui, H. G. et al. Spontaneous and X-ray-triggered crystallization at long range in self-assembling filament networks. Science 327, 555–559 (2010)

    CAS  Article  ADS  Google Scholar 

  8. 8

    Palmer, L. C. et al. Long-range ordering of highly charged self-assembled nanofilaments. J. Am. Chem. Soc. 136, 14377–14380 (2014)

    CAS  Article  Google Scholar 

  9. 9

    Wu, Z. L. et al. Anisotropic hydrogel from complexation-driven reorientation of semirigid polyanion at Ca2+ diffusion flux front. Macromolecules 44, 3535–3541 (2011)

    CAS  Article  ADS  Google Scholar 

  10. 10

    Wu, J., Zhao, Q., Sun, J. & Zhou, Q. Preparation of poly(ethylene glycol) aligned porous cryogels using a unidirectional freezing technique. Soft Matter 8, 3620–3626 (2012)

    CAS  Article  ADS  Google Scholar 

  11. 11

    Liu, M., Ishida, Y., Ebina, Y., Sasaki, T. & Aida, T. Photolatently modulable hydrogels using unilamellar titania nanosheets as photocatalytic crosslinker. Nature Commun. 4, 2029 (2013)

    Article  ADS  Google Scholar 

  12. 12

    Eguchi, M., Angelone, M. S., Yennawar, H. P. & Mallouk, T. E. Anisotropic alignment of lamellar potassium hexaniobate microcrystals and nanoscrolls in a static magnetic field. J. Phys. Chem. C 112, 11280–11285 (2008)

    CAS  Article  Google Scholar 

  13. 13

    Ida, S. et al. Photoluminescence of perovskite nanosheets prepared by exfoliation of layered oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion). J. Am. Chem. Soc. 130, 7052–7059 (2008)

    CAS  Article  Google Scholar 

  14. 14

    Osada, M. et al. Ferromagnetism in two-dimensional Ti0. 8Co0. 2O2 nanosheets. Phys. Rev. B 73, 153301 (2006)

    Article  ADS  Google Scholar 

  15. 15

    Prosser, S., Hunt, S. A., DiNatale, J. A. & Vold, R. R. Magnetically aligned membrane model systems with positive order parameter: switching the sign of S zz with paramagnetic ions. J. Am. Chem. Soc. 118, 269–270 (1996)

    CAS  Article  Google Scholar 

  16. 16

    Tan, C., Fung, B. M. & Cho, G. Phospholipid bicelles that align with their normals parallel to the magnetic field. J. Am. Chem. Soc. 124, 11827–11832 (2002)

    CAS  Article  Google Scholar 

  17. 17

    Kleinschmidt, F., Hickl, M., Saalwächter, K., Schmidt, C. & Finkelmann, H. Lamellar liquid single crystal hydrogels: synthesis and investigation of anisotropic water diffusion and swelling. Macromolecules 38, 9772–9782 (2005)

    CAS  Article  ADS  Google Scholar 

  18. 18

    Haque, M. A., Kamita, G., Kurokawa, T., Tsujii, K. & Gong, J. P. Unidirectional alignment of lamellar bilayer in hydrogel: one-dimensional swelling, anisotropic modulus, and stress/strain tunable structural color. Adv. Mater. 22, 5110–5114 (2010)

    CAS  Article  Google Scholar 

  19. 19

    Erb, R. M., Libanori, R., Rothfuchs, N. & Studart, A. R. Composites reinforced in three dimensions by using low magnetic fields. Science 335, 199–204 (2012)

    MathSciNet  CAS  Article  ADS  Google Scholar 

  20. 20

    Wang, Q. et al. High-water-content mouldable hydrogels by mixing clay and a dendritic molecular binder. Nature 463, 339–343 (2010)

    CAS  Article  ADS  Google Scholar 

  21. 21

    Tamesue, S. et al. Linear versus dendritic molecular binders for hydrogel network formation with clay nanosheets: studies with ABA triblock copolyethers carrying guanidinium ion pendants. J. Am. Chem. Soc. 135, 15650–15655 (2013)

    CAS  Article  Google Scholar 

  22. 22

    Maret, G. & Dransfeld, K. Biomolecules and polymers in high steady magnetic fields. Top. Appl. Phys. 57, 143–204 (1985)

    CAS  Article  Google Scholar 

  23. 23

    Löwen, H. Colloidal soft matter under external control. J. Phys. Condens. Matter 13, R415–R432 (2001)

    Article  ADS  Google Scholar 

  24. 24

    Uyeda, C. Diamagnetic anisotropies of oxide minerals. Phys. Chem. Miner. 20, 77–81 (1993)

    CAS  ADS  Google Scholar 

  25. 25

    Torbet, J., Freyssinet, J. M. & Hudry-Clergeon, G. Oriented fibrin gels formed by polymerization in strong magnetic fields. Nature 289, 91–93 (1981)

    CAS  Article  ADS  Google Scholar 

  26. 26

    Feng, S. et al. Hierarchical structure in oriented fibers of a dendronized polymer. Macromolecules 42, 281–287 (2009)

    CAS  Article  ADS  Google Scholar 

  27. 27

    Verwey, E. J. W. & Overbeek, J. Th. G. Theory of the Stability of Lyophobic Colloids (Elsevier, 1948)

    Google Scholar 

  28. 28

    Podsiadlo, P. et al. Ultrastrong and stiff layered polymer nanocomposites. Science 318, 80–83 (2007)

    CAS  Article  ADS  Google Scholar 

  29. 29

    Munch, E. et al. Tough, bio-inspired hybrid materials. Science 322, 1516–1520 (2008)

    CAS  Article  ADS  Google Scholar 

  30. 30

    Budtova, T. & Navard, P. Swelling-induced birefringence of a polyelectrolyte gel strongly interacting with metal ions. Macromolecules 30, 6556–6558 (1997)

    CAS  Article  ADS  Google Scholar 

Download references


This work was financially supported by a Grant-in-Aid for Specially Promoted Research (25000005) on “Physically Perturbed Assembly for Tailoring High-Performance Soft Materials with Controlled Macroscopic Structural Anisotropy”. We also acknowledge the ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan). The synchrotron X-ray diffraction experiments were performed at BL45XU in SPring-8 with the approval of the RIKEN SPring-8 Center (proposal 20140073).

Author information




M.L. designed and performed all experiments. Y.I. and T.A. co-designed the experiments. Y.E. and T.S. prepared colloidally dispersed TiNSs and NbNSs. M.L., Y.I. and T.A. analysed the data and wrote the manuscript. T.H. and M.T. supported the X-ray diffraction measurements at SPring-8.

Corresponding authors

Correspondence to Yasuhiro Ishida or Takuzo Aida.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figures 1–18, Supplementary Tables 1-2 and Supplementary References. (PDF 9710 kb)

Vibration isolation of hydrogel pillars containing horizontally oriented TiNSs.

This video shows the vibration isolation of hydrogel pillars containing horizontally oriented TiNSs. (MOV 5745 kb)

Vibration isolation of hydrogel pillars containing vertically oriented TiNSs

This video shows the vibration isolation of hydrogel pillars containing vertically oriented TiNSs. (MOV 2480 kb)

Vibration isolation of hydrogel pillars containing randomly oriented TiNSs

This video shows the vibration isolation of hydrogel pillars containing randomly oriented TiNSs. (MOV 4334 kb)

Oscillation-induced deformations of single hydrogel cylinders without any weight at their free edge

This video shows the oscillation-induced deformations of single hydrogel cylinders without any weight at their free edge. (MOV 31453 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Liu, M., Ishida, Y., Ebina, Y. et al. An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets. Nature 517, 68–72 (2015).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing