Chemical actuation in responsive hydrogels

Chemically actuated hydrogels share a unique feature with living systems: they are both driven by their ability to convert chemical energy into a mechanical response. However, macroscopic applications of hydrogels are limited due to the slow response rate of these materials. This problem has been overcome by developing materials at micrometre length scales, as the diffusion kinetics are related to the square of the size of the smallest dimension of the gel. Herein, the progress in the field of chemical actuation in hydrogel systems is reviewed, with an emphasis on the ways in which new devices have been designed.