Fig. 1

Illustration of the intervertebral disc pre-treatment and the bioreactor system used for the rabbit disc cultures. a Rabbit discs with cartilage endplates were isolated and assigned to the experimental group (EG) or control group (CG). First, approximately the outermost one-third of the annulus fibrosus (AF) of the discs in the EG, but not in the CG, was removed (a). Then, the discs in the EG were placed in a 0.25 % trypsin solution to loosen the network of superficial AF, while the discs in the CG were placed in DMEM/F12 medium (b). After trypsinization, the digested superficial AF tissue in the EG was cut out (c). Finally, all discs were cultured in the chambers of a self-developed bioreactor system. b Overview of the bioreactor system, which consists of the five labeled functional units