A method of treating an intervertebral disc of a subject is provided, comprising implanting, within a nucleus pulposus of the disc, at least three intra-pulposus exposed electrode surfaces at different respective locations； and implanting one or more extra-pulposus exposed electrode surfaces outside the nucleus pulposus, in electrical communication with the disc. Control circuitry is activated to configure the intra-pulposus exposed electrode surfaces to be cathodes, and the one or more extra-pulposus exposed electrode surfaces to be one or more anodes, and to drive the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces to electroosmotically drive fluid into the nucleus pulposus to increase pressure in the disc. Other embodiments are also described.
