Dry, but not too dry, hydrogels are naturally heating/water-responsive SMP ​
​Thermo-/chemo-responsive shape memory/change effect in a hydrogel and its composites, Materials and Design, Vol. 53, 2014, 1077-1088
Surface wetting, then drying in air

(Wet hydrogel)
Shape fixed in fridge at ​-20°C

​(a) Original shape; (b) after bent and kept at -20°C for one hour; (c-e) shape recovery sequence at around 25°C; (f) after immersed in room temperature water for 30 minutes.

Water-baby
​Thermo-/chemo-responsive shape memory/change effect in a hydrogel and its composites, Materials and Design, Vol. 53, 2014, 1077-1088
Shape memory effect in elastic hydrogels
Gradual recovery in 2 mins in air after cooled in fridge for 1 h.
(FYP) Ng JK, Shaw
Dry/wet hydrpgels in PEG solution of different concentrations and then drying

Water induced shrinkage

Toughgel
​Shape memory/change effect in a double network nanocomposite tough hydrogel, European Polymer Journal, 58, 2014, 41-51

Cross-linked P407
Low temperature programming (low temperature recovery)
Room temperature programming (low Temp + water recovery)
Comparison of recovery via dry cooling and wetting in room temperature water of room temperature folded samples.
Water content dependent cooling/heating and water responsive shape memory hydrogel
​Rapid volumetric additive manufacturing in solid-state: a demonstration to produce water-content dependent cooling/heating/water-responsive shape memory hydrogels

自制燕窝
Drying over time

Weed grows atop hydrogel
​可控接触破坏水凝胶驱动器
​Controllable Contact-Destructive Hydrogel Actuators
​Constructing hydrogels with spatially heterogeneous structures are crucial for unlocking novel applications. To this end, selectively removing a specific portion of hydrogels by facile and intricate destructive strategies is worth exploring. Herein, a “contact-destructive” hydrogel actuator is presented, composed of a dynamic hydrogel network doped with hydrophilic polyethylene glycol (PEG). The destructive behavior of the hydrogel actuator is attributed to the surface tension-induced spreading effect and the enhanced water absorption due to the additive PEG. Parameters that act on these mechanisms are used to control the destruction of the hydrogel. During the destructive process, the hydrogel actuator exhibits locomotion routes predetermined by the graphic pattern with the aid of 3D printing. Additionally, such self-destructive behavior can be terminated by UV light irradiation when PEG is replaced with poly(ethylene glycol) diacrylate (PEGDA). Significantly, diverse applications including controllable 3D structures collapse, self-erasing, and on-demand cell release, are realized with such self-destructive hydrogel. These results demonstrate that the present hydrogel has great values in soft robotics, anti-counterfeiting, controlled drug delivery, and other related fields.