The device shown is driven by changes in pH in the surrounding solution.

It consists of two membranes perforated by small holes, the membranes are coated with two different functional polymers: The poly(amine) swells in acidic solution, while the poly(carboxylic acid) swells in base.

As the pH changes the two polymers act to open and close pores on the facing membranes, and change the separation between them in a concerted fashion - so acting as a pump.