Figure 2

Regenerative treatment strategies for intervertebral disc (IVD) degeneration. Upper left: in vitro cell cultures: monolayer (2D), pellet culture (3D), filter culture (3D), and cell-containing alginate beads (3D). Upper right: the in vitro nucleus pulposus (NP) explant culture system, in which the NP is cultured in an artificial annulus system. As the artificial annulus may be buoyant, a stainless steel cylinder is added to keep the NP submerged. Lower right: the in vitro loaded culture disc system, in which intact IVD explants are cultured under loading conditions with preservation of biological and structural integrity. Lower left: in vivo animal models, e.g., the rabbit, in which IVD degeneration is often experimentally induced, and the Beagle (chondrodystrophic dog breed), which develops spontaneous IVD degeneration from 1 year of age (right). Pictures of the rabbit and Beagle are obtained from Depositphotos (http://depositphotos.com).