Apparatus is provided that includes one or more intra-pulposus exposed electrode surfaces, and a support structure along which the one or more intra-pulposus exposed electrode surfaces are disposed. The support structure is configured to be implanted within a nucleus pulposus of an intervertebral disc of a subject, and to be shaped as a partial ring or a complete ring after implantation. The apparatus further includes one or more extra-pulposus exposed electrode surfaces, which are configured to be implanted outside the nucleus pulposus, in electrical communication with the disc. Control circuitry is provided, which is configured 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 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. Other embodiments are also described.
