An implantable medical device is described. The implantable medical device includes a small molecule generator, a small molecule diffusor, and a cannula that connects the two. The small molecule generator includes an electrolyte reservoir and a set of electrodes. A first portion of the electrolyte reservoir is impermeable to a predetermined class of small molecules. A second portion of the electrolyte reservoir is permeable to the small molecules. The set of electrodes is disposed inside the electrolyte reservoir and is configured to facilitate electrolysis of the small molecules based on an electric power application to the set of electrodes and on presence of electrolyte inside the electrolyte reservoir. At least a portion of the small molecule diffusor is permeable to the small molecules.