Provided is an ex-vivo method of producing an enriched cell population comprising the steps of plating a heterogeneous population of nucleus pulposus cells in a media at low cell density； growing the cells under conditions that inhibit cell attachment； selecting free-floating in vitro spherical structures comprising disc stem cells, disc progenitor cells, or a mixture thereof； thereby producing an enriched cell population. An ex-vivo method of expanding a population of disc stem cells, disc progenitor cells, or a mixture thereof is also provided, as is an ex-vivo method of producing an artificial disc and methods of treating a subject having a damaged intervertebral disc.
