The present invention provides a prosthetic cover (12) shaped to form a replacement nucleus pulposis (56) for an intervertebral disc (50), said cover comprising a permeable layer of an immunologically neutral material terminating in a valve structure (16) to allow the introduction of a hydrogel material...http://www.google.com/patents/US6402784?utm_source=gb-gplus-sharePatent US6402784 - Intervertebral disc nucleus prosthesis
