Functional Validation of a Complex Loading Whole Spinal Segment Bioreactor Design.

Intervertebral disk (IVD) degeneration is a prevalent health problem that is highly linked to back pain. To understand the disease and tissue response to therapies, ex vivo whole IVD organ culture systems have recently been introduced. The goal of this work was to develop and validate the design of a whole spinal segment culturing system that loads the disk in complex loading similar to the in vivo condition, while preserving the adjacent endplates and vertebral bodies. The complex loading applied to the spinal segment (flexion-extension (FE), bilateral bending, and compression) was achieved with three pneumatic cylinders rigidly attached to a triangular loading platform. A culture container housed the spinal segment and was attached to the loading mechanism, which allowed for loading of the spinal segment. The dynamic bioreactor was able to achieve physiologic loading conditions with 100 N of applied compression and approximately 2-4 N · m of applied torque. The function of the bioreactor was validated through testing of bovine caudal IVDs with intact endplates and vertebral bodies that were isolated within 2 hrs of death and cultured for 14 days. The resulting IVD cell viability following 14 days of loading was much higher than unloaded control IVDs. The loading system accurately mimicked FE, bilateral bending, and compression motions seen during daily activities. The results indicate that this complex dynamic bioreactor may be appropriate for extended preclinical testing of vertebral-mounted spinal devices and therapies.