An actuator that includes an enclosure having a wall impermeable to a first solute and permeable to a solvent and containing, at least temporarily, a catalyst capable of promoting the transformation of at least one second solute into the first solute to vary the osmotic pressure in the enclosure; and a deformable chamber connected to the enclosure, the chamber being capable of increasing in volume under the action of the solvent moving from the enclosure into the chamber by osmosis or the enclosure being designed to be arranged in contact with the solvent, the chamber being capable of increasing in volume under the action of the solvent penetrating into the enclosure by osmosis.