Apparatus is provided which includes a housing (24), configured for insertion into a body of a subject. The apparatus includes functional cells (32) coupled to the housing (24) and a source of oxygen configured to supply oxygen to the functional cells. The apparatus further includes an oxygen delivery interface (27) configured to receive oxygen from the source of oxygen, and to facilitate passage of the oxygen to the functional cells (32), while the housing (24) is disposed within the body of the subject. Other applications are also described.
