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 paper1 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.
Clay-NS (Laponite XLG) was purchased from Rockwood Ltd.
ASAP (sodium polyacrylate) was purchased from Wako Pure Chemical Industries, Ltd.
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.
Ultrapure-grade water was used for hydrogelation.
Teflon-coated magnetic stirrer bar
Water purification system (Milli-Q, Nihon Millipore K.K.)
A typical example of the hydrogelation with Clay-NS, ASAP, and Gn-binder is given below:
- Dissolve 3.0 mg of sodium polyacrylate (ASAP) in 1.0 mL of water.
- Dissolve 7.5 mg of G3-binder in 0.25 mL of water.
- Suspend 100 mg of Clay-NS to 3.75 mL of water.
- Stir the suspension of Clay-NS at room temperature such as 20 oC.
- Add 1.0 mL of the aqueous solution of ASAP to the stirred suspension of Clay-NS at room temperature such as 20 oC.
- 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.
- Dropwise add 0.25 mL of the aqueous solution of G3-binder to the vigorously stirred Clay-NS/ASAP solution.
- Let the resultant solution stand for 3 minutes and obtain a transparent, self-standing gel.
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.
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.