Bioinspired gradient hydrogel actuators with rewritable patterns and programmable shape deformation

The botanical world inspires scientists to develop various smart actuators with diverse mechanical motions in response to external stimuli. However, it is challenging to obtain programmable and reversible hydrogel actuators. Herein, we presented a bioinspired nanocomposite hydrogel composed of poly(NIPAM-co-AA) and tunicate cellulose nanocrystals (TCNCs). A direct current electric field (DC-EF) was applied to induce controllable distribution of the TCNCs via electrophoresis for the formation of a gradient structure. To mimic the leaflet structure of Mimosa pudica, the patterns written using a lye pen on the hydrogel acted as the pinnae of leaves, while the residual regions worked as the rachis parts. With the increase of temperature, the rachis area of the nanocomposite hydrogel exhibited a large bending deformation because the gradient distribution of TCNCs induced asymmetric shrinkage, whereas the pinnae changed slightly because -COO-/-COO- electrostatic repulsion maintained the swelling state of the hydrogel network, like the leaflet folding of Mimosa pudica. Furthermore, these bioinspired hydrogel actuators with erasable and rewritable patterns exhibited programmable deformation, good stability, and good cycling performance. This work provided a facile yet efficient strategy for the fabrication of hydrogel actuators with rewritable patterns and programmable shape deformations.

Automated summary

Inspired by the botanical world, scientists have developed a bioinspired nanocomposite hydrogel with controllable shape deformation and rewritable patterns. The gradient distribution of TCNCs induced asymmetrical shrinkage in the hydrogel, mimicking the leaflet folding of Mimosa pudica. These actuators demonstrated good stability and cycling performance, providing a facile yet efficient strategy for programmable and reversible hydrogel actuators.