Synthetic Chemistry Chemical Modification Nanotechnology

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Authors: Qigang Wang, Justin Mynar & Takuzo Aida

Introduction

This protocol describes a facile, quick and reproducible preparation of hydrogels. The protocol requires four components: water, clay nanosheets (Clay-NS), a dendritic macromolecule (Gn-binder; n = generation number) and sodium polyacrylate (ASAP). Upon mixing with ASAP in water, Clay-NS, which are heavily entangled with one another, are exfoliated and dispersed homogenously because of a possible site-specific wrapping of their positive-charged edge parts with anionic ASAP. Meanwhile, Gn-binder possesses two dendron units, which are decorated with multiple guanidinium ion pendants on their periphery. A previous paper (1) reports that a mono-dendron version of Gn-binder interacts strongly with the oxyanionic surface groups of proteins. Upon addition of Gn-binder to the aqueous solution of Clay-NS with ASAP, exfoliated nanosheets of clay are crosslinked kinetically through multivalent salt-bridge formation between the guanidinium ion pendants of Gn-binder and oxyanionic groups on the nanosheet surface. Consequently, the hydrogelation takes place.

Reagents

  1. Clay-NS (Laponite XLG) was purchased from Rockwood Ltd.
  2. ASAP (sodium polyacrylate) was purchased from Wako Pure Chemical Industries, Ltd.
  3. Gn-binder was synthesized through an adapted synthetic protocol of previous literatures. (1,2) For details, see Supplementary Information of the related article in Nature.
  4. Ultrapure-grade water was used for hydrogelation.

Equipment

  1. Magnetic stirrer
  2. Teflon-coated magnetic stirrer bar
  3. Plastic vial
  4. Water purification system (Milli-Q, Nihon Millipore K.K.)

Procedure

A typical example of the hydrogelation with Clay-NS, ASAP, and Gn-binder is given below:

  1. Dissolve 3.0 mg of sodium polyacrylate (ASAP) in 1.0 mL of water.
  2. Dissolve 7.5 mg of G3-binder in 0.25 mL of water.
  3. Suspend 100 mg of Clay-NS to 3.75 mL of water.
  4. Stir the suspension of Clay-NS at room temperature such as 20 oC.
  5. Add 1.0 mL of the aqueous solution of ASAP to the stirred suspension of Clay-NS at room temperature such as 20 oC.
  6. Stir the ASAP-containing Clay-NS suspension for 10 minutes at room temperature such as 20 oC and confirm that it turns into a clear viscous solution.
  7. Dropwise add 0.25 mL of the aqueous solution of G3-binder to the vigorously stirred Clay-NS/ASAP solution.
  8. Let the resultant solution stand for 3 minutes and obtain a transparent, self-standing gel.

Timing

Approximately 13 minutes

Magnetic stirring of an aqueous suspension of Clay-NS after addition of ASAP (dispersion of Clay-NS); approximately 10 minutes, Magnetic stirring of the resulting dispersion after addition of G3-binder; approximately 1 minute, Standing of the resulting mixture (hydrogelation); approximately 2 minutes.

Troubleshooting

Gn-binder is highly adhesive to glass:

  • a) Leave Gn-binder protected until ready for hydrogelation.
  • b) Use plastic vials and containers when performing hydrogelation.
  • c) Powerful and efficient stirring is helpful for accelerating the exfoliation of Clay-NS and hydrogelation. However, air-bubbles occasionally form in the resulting hydrogel.

References

  1. Okuro, K., Kinbara, K., Tsumoto, K., Ishii, N. & Aida, T. Molecular glues carrying multiple guanidinium ion pendants via oligoether spacer: stabilization of microtubules against depolymerization. J. Am. Chem. Soc. 131, 1626-1627 (2009).
  2. Ihre, H., Padilla De Jesus, O. L. & Fréchet, J. M. J. Fast and convenient divergent synthesis of aliphatic ester dendrimers by anhydride coupling. J. Am. Chem. Soc. 123, 5908-5917 (2001).

Associated Publications

High-water-content mouldable hydrogels by mixing clay and a dendritic molecular binder, Qigang Wang, Justin L. Mynar, Masaru Yoshida, Eunji Lee, Myongsoo Lee, Kou Okuro, Kazushi Kinbara, and Takuzo Aida, Nature 463 (7279) 339 - 343 21/01/2010 doi:10.1038/nature08693

Author information

Qigang Wang, The University of Tokyo

Justin Mynar & Takuzo Aida, JST ERATO-SORST and The University of Tokyo

Source: Protocol Exchange (2010) doi:10.1038/nprot.2010.23. Originally published online 22 January 2010.

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