A polymer gel with electrically driven motility

Abstract

A SYSTEM capable of converting chemical energy to mechanical energy could serve as an actuator or an 'artificial muscle' in several applications. Here we describe a chemomechanical system of this sort based on a synthetic polymer gel. The gel network is anionic, and positively charged surfactant molecules can therefore bind to its surface, inducing local shrinkage by decreasing the difference in osmotic pressure between the gel interior and the solution outside. By using an electric field to direct surfactant binding selectively to one side of the gel, we can induce contraction and curvature of a strip of gel. Reversing the direction of the field causes contraction of the opposite side, and when the gel is suspended in solution from a ratchet mechanism, it can thereby be made to move with a worm-like motion at a velocity of up to 25 cm min⁻¹.