Swellable compositions and methods of using and controlling them are disclosed. In certain examples, the swellable composition may comprise an active phase responsive to swell upon exposure to a swelling fluid. In some examples, the active phase of the swellable composition is effective to deswell in response to an applied stimulus in the presence of the swelling fluid. In other examples, the swellable composition may further comprise a passive phase responsive to swell to a lesser degree than the active phase upon exposure to the swelling fluid. Devices and systems using the swellable compositions are also described.