that at pH 7. The different swelling extent drives the bilayer to bend toward the
P(NaMAA-co-HEMA) side, leading to the formation of a ring (Fig. 22c). Upon
immersing in pH 7 solution, the bilayer slowly recovers to its original state.
Second, the macroscopic assembling was further utilized to fabricate assembled
devices with patterned structures (Fig. 22d). For example, the P(DMAEMA-coHEMA) patches (width ¼ 5 mm, thickness ¼ 1.5 mm) are periodically assembled on
the P(NaMAA-co-HEMA) (200 Â 10 Â 1.5 mm) surface with an angle of 45
and a
spacing of 5 mm (Fig. 22e). The periodic structures with different swelling properties produce an internal stress upon immersing in a solution of pH 5, which drives a
transformation from planar shape to a helix in about 320 min (Fig. 22f–h). Herein,
the internal stress is rendered by the periodic swelling contrast of polycationic and
polyanionic gels [58]. The facile fabrication could be used for a convenient fabrication of 3D structures by properly engineering the hydrogel sheet dimensions and/or
the periodicity and the size of the patches.
5 Supramolecular Micelle-Crosslinked Hydrogels
The hydroxyl end groups of F127 triblock copolymer can be modified with many
other functional groups. The modified F127 chains self-assemble in aqueous solutions into polyfunctional micelles. The obtained micelles are able to link with
polymer chains through supramolecular recognition, dynamic bonds, and noncovalent bonding, just to name a few. It offers great opportunities to design the
crosslinking method and particularly to tune the mechanical, self-healing, and
recovery properties.
Chen et al. functionalized the F127 copolymer by attaching aldehyde groups on
both ends (Fig. 23) [18]. In aqueous solutions, the modified F127 chains selfassemble into micelles with abundant aldehyde groups in the coronae. Aldehydes
are known to form dynamic acylhydrazone bonds with acylhydrazine groups
[59]. The modified micelles were employed as multifunctional crosslinkers to
bond with three-armed poly(ethylene glycol) (PEG) with acylhydrazine end groups,
leading to the formation of hydrogels (Fig. 23). Different from the F127DA micellecrosslinked hydrogels, the use of aldehyde-functionalized F127 micelles and threearm polymers produces hydrogels crosslinked by hydrophobic association and
chemical bonding. The dual crosslinking is coupled through the dynamic
acylhydrazone bonds. Although the molecular weight of PEG is relatively low, the
obtained hydrogels show an extremely high stretchability up to 117 times of its
original length. The dynamic hydrophobic association and acylhydrazone bonding
work together to provide a large amount of energy dissipation, as featured by the
large hysteresis loops upon tensile loading-unloading tests. It is assumed that the
chain sliding in the micelles may account for the extremely high stretchability.
However, it takes about 3 days to achieve about 90% recovery at room temperature,
presumably due to the re-establishment of the acylhydrazone bonds in the networks.
Triblock Copolymer Micelle-Crosslinked Hydrogels
235
P(NaMAA-co-HEMA) side, leading to the formation of a ring (Fig. 22c). Upon
immersing in pH 7 solution, the bilayer slowly recovers to its original state.
Second, the macroscopic assembling was further utilized to fabricate assembled
devices with patterned structures (Fig. 22d). For example, the P(DMAEMA-coHEMA) patches (width ¼ 5 mm, thickness ¼ 1.5 mm) are periodically assembled on
the P(NaMAA-co-HEMA) (200 Â 10 Â 1.5 mm) surface with an angle of 45
and a
spacing of 5 mm (Fig. 22e). The periodic structures with different swelling properties produce an internal stress upon immersing in a solution of pH 5, which drives a
transformation from planar shape to a helix in about 320 min (Fig. 22f–h). Herein,
the internal stress is rendered by the periodic swelling contrast of polycationic and
polyanionic gels [58]. The facile fabrication could be used for a convenient fabrication of 3D structures by properly engineering the hydrogel sheet dimensions and/or
the periodicity and the size of the patches.
5 Supramolecular Micelle-Crosslinked Hydrogels
The hydroxyl end groups of F127 triblock copolymer can be modified with many
other functional groups. The modified F127 chains self-assemble in aqueous solutions into polyfunctional micelles. The obtained micelles are able to link with
polymer chains through supramolecular recognition, dynamic bonds, and noncovalent bonding, just to name a few. It offers great opportunities to design the
crosslinking method and particularly to tune the mechanical, self-healing, and
recovery properties.
Chen et al. functionalized the F127 copolymer by attaching aldehyde groups on
both ends (Fig. 23) [18]. In aqueous solutions, the modified F127 chains selfassemble into micelles with abundant aldehyde groups in the coronae. Aldehydes
are known to form dynamic acylhydrazone bonds with acylhydrazine groups
[59]. The modified micelles were employed as multifunctional crosslinkers to
bond with three-armed poly(ethylene glycol) (PEG) with acylhydrazine end groups,
leading to the formation of hydrogels (Fig. 23). Different from the F127DA micellecrosslinked hydrogels, the use of aldehyde-functionalized F127 micelles and threearm polymers produces hydrogels crosslinked by hydrophobic association and
chemical bonding. The dual crosslinking is coupled through the dynamic
acylhydrazone bonds. Although the molecular weight of PEG is relatively low, the
obtained hydrogels show an extremely high stretchability up to 117 times of its
original length. The dynamic hydrophobic association and acylhydrazone bonding
work together to provide a large amount of energy dissipation, as featured by the
large hysteresis loops upon tensile loading-unloading tests. It is assumed that the
chain sliding in the micelles may account for the extremely high stretchability.
However, it takes about 3 days to achieve about 90% recovery at room temperature,
presumably due to the re-establishment of the acylhydrazone bonds in the networks.
Triblock Copolymer Micelle-Crosslinked Hydrogels
235