rings (α-CD, β-CD, γ-CD and their olefin derivatives [41–43]), and the cross-linker
molecules (isocyanates, olefins, alkynes, etc. [44–46]). In general, most of the polymer
chains used in CD PR gels are water-soluble polymers. Wenz et al [47]. for the first
time used CD-binding isoprene complexes as monomers to synthesize PPRs by
one-pot radical polymerization, and then styrene molecules were used as blocking
agents, thus forming PRs. Finally, a “slide-ring” hydrogel with high viscoelasticity
was successfully constructed via cyclohexane diisocyanate-cross-linked PRs. In summary, through the combination of covalent binding and non-covalent binding of PRs,
the novel architecture of the cross-linking structures will provide a new strategy for
hydrogel fabrication.
Ionic interaction, as an important type of electrostatic interaction, plays an
important role in the construction of supramolecular hydrogels. Taking advantage
of the ion-driven self-assembly process in the gel state can provide a novel approach
for the construction of three-dimensional smart CD hydrogel material. Our group
[16] has successfully developed an organic-inorganic hybrid hydrogel by combining
laponite and PPRs of thiol-modified β-CD and PPG (Fig. 4). The hydrogel with high
water content processed self-healing ability, and its mechanical strength could be
easily adjusted. The introduction of the PPR structure as a cross-linker for the
laponite not only avoided the complicated synthesis process to a great extent but
also endowed the hydrogel controllable mechanical properties.
17.2.2 CD Gels Based on Complexation with Small Guest Molecules
The host-guest interaction is another widely used non-covalent interaction in the
construction of supramolecular CD gels. When the sizes of the CD cavity and guest
molecule matched well with each other, the more hydrophobic the guest molecule is,
the more stable inclusion complex will form. Hu et al. [13] reported a kind of
pentacyclic triterpene compound, glycyrrhetinic acid (GA), which could form a
1:1 inclusion complex with β-CD. Based on this host-guest pair, GAs and β-CDs
were grafted on poly(N,N
0 -dimethyl acrylamide), respectively, and then two modified polymers were mixed in water to gain a CD hydrogel via host-guest interaction
(Fig. 5). When supramolecular hydrogel formed from gelators with 15% mass
fraction and the GA to β-CD molar ratio of 1:1, the storage modulus of the CD
hydrogel reached its maximum, while the energy consumption modulus remained
almost unchanged. This supramolecular CD hydrogel exhibits rapid self-healing
property and extremely good biocompatibility, suggesting its potential application
value in the field of tissue engineering.
β-CD and bile acid were reported to form stable 1:1 host-guest inclusion complexes. At the same time, poly(vinyl alcohol) (PVA), as a common biocompatible
polymer, has been widely used for the preparation of hydrogels. Jia et al. [48]
covalently attached bile acids and β-CDs to low molecular weight PVA polymers
separately, and then two derivatized PVA polymers were mixed, thus forming a selfhealing hydrogel easily (Fig. 6), which were quite convenient than the traditional
hydrogels prepared by freeze-thaw method. The hydrogels’ mechanical properties
17 Cyclodextrin-Based Supramolecular Hydrogel
487
molecules (isocyanates, olefins, alkynes, etc. [44–46]). In general, most of the polymer
chains used in CD PR gels are water-soluble polymers. Wenz et al [47]. for the first
time used CD-binding isoprene complexes as monomers to synthesize PPRs by
one-pot radical polymerization, and then styrene molecules were used as blocking
agents, thus forming PRs. Finally, a “slide-ring” hydrogel with high viscoelasticity
was successfully constructed via cyclohexane diisocyanate-cross-linked PRs. In summary, through the combination of covalent binding and non-covalent binding of PRs,
the novel architecture of the cross-linking structures will provide a new strategy for
hydrogel fabrication.
Ionic interaction, as an important type of electrostatic interaction, plays an
important role in the construction of supramolecular hydrogels. Taking advantage
of the ion-driven self-assembly process in the gel state can provide a novel approach
for the construction of three-dimensional smart CD hydrogel material. Our group
[16] has successfully developed an organic-inorganic hybrid hydrogel by combining
laponite and PPRs of thiol-modified β-CD and PPG (Fig. 4). The hydrogel with high
water content processed self-healing ability, and its mechanical strength could be
easily adjusted. The introduction of the PPR structure as a cross-linker for the
laponite not only avoided the complicated synthesis process to a great extent but
also endowed the hydrogel controllable mechanical properties.
17.2.2 CD Gels Based on Complexation with Small Guest Molecules
The host-guest interaction is another widely used non-covalent interaction in the
construction of supramolecular CD gels. When the sizes of the CD cavity and guest
molecule matched well with each other, the more hydrophobic the guest molecule is,
the more stable inclusion complex will form. Hu et al. [13] reported a kind of
pentacyclic triterpene compound, glycyrrhetinic acid (GA), which could form a
1:1 inclusion complex with β-CD. Based on this host-guest pair, GAs and β-CDs
were grafted on poly(N,N
0 -dimethyl acrylamide), respectively, and then two modified polymers were mixed in water to gain a CD hydrogel via host-guest interaction
(Fig. 5). When supramolecular hydrogel formed from gelators with 15% mass
fraction and the GA to β-CD molar ratio of 1:1, the storage modulus of the CD
hydrogel reached its maximum, while the energy consumption modulus remained
almost unchanged. This supramolecular CD hydrogel exhibits rapid self-healing
property and extremely good biocompatibility, suggesting its potential application
value in the field of tissue engineering.
β-CD and bile acid were reported to form stable 1:1 host-guest inclusion complexes. At the same time, poly(vinyl alcohol) (PVA), as a common biocompatible
polymer, has been widely used for the preparation of hydrogels. Jia et al. [48]
covalently attached bile acids and β-CDs to low molecular weight PVA polymers
separately, and then two derivatized PVA polymers were mixed, thus forming a selfhealing hydrogel easily (Fig. 6), which were quite convenient than the traditional
hydrogels prepared by freeze-thaw method. The hydrogels’ mechanical properties
17 Cyclodextrin-Based Supramolecular Hydrogel
487