An implantable device for delivering a therapeutic agent to a patient is provided. The device includes a reservoir configured to contain a liquid comprising the therapeutic agent. The device further includes a cannula in fluid communication with the reservoir. The cannula has an outlet configured to be in fluid communication with the patient. The device further includes a first electrode and a second electrode, at least one of the first electrode and the second electrode is planar. The device further includes a material in electrical communication with the first and second electrodes. A voltage applied between the first electrode and the second electrode produces gas from the material, the gas forcing the liquid to flow from the reservoir to the outlet.