Optimization of Bioreactor Design for Normal Loading of Human Intervertebral Disks

• Published in: Global spine journal 2012-06, Vol.2 (1_suppl), p.s-0032-1319929-s-0032-1319929
• Main Authors: Gawri, R., Althukair, R., Moir, J., Roughley, P., Ouellet, J., Steffen, T., Haglund, L. A.
• Format: Article
• Language: English
• ISSN: 2192-5682; 2192-5690
• DOI: 10.1055/s-0032-1319929

Introduction Intervertebral disk (IVD) degeneration is a common cause of back pain, which has a negative impact on the quality of life of the patient and is costly to the health care system. It is crucial to understand the interplay between mechanobiology, disk composition, and metabolism to understand the underlying cause of disk degeneration and to be able to study ways to regenerate the degenerate disk. To address such questions, a bioreactor has been developed that facilitates organ culture of intact human disks in a controlled dynamically loaded environment. The bioreactor is used in combination with an isolation method which maintains the integrity of the intervertebral disks by preserving the noncalcified part of the cartilage endplate. In this study, stress profilometry was used to evaluate optimal loading platen design for the bioreactor. Materials and Methods Human lumbar IVDs were obtained through organ donations via Transplant Quebec. The spines were assessed by X-ray to evaluate the degree of degeneration. Intact disks were prepared by parallel cuts through the adjacent vertebral bodies close to the end plates, and the remaining bone and the calcified part of the cartilage endplates were removed using a high-speed bone burr. Pictures of the disk were taken after processing and surface area was calculated with ImageJ software to calculate the load to be applied to generate pressures of 0.3 MPa and 0.6 MPa. Two platen sets were tested, full coverage of the whole disk and partial coverage of only the nucleus pulposus (NP) region. The disks were mounted between two platens and stress profiles were recorded at 0.3 MPa and 0.6 MPa static load. Vertical (V) and horizontal (H) stress profiles were generated for anterior-posterior (AP) and lateral diameters of the disk. Results In young and healthy isolated disks, stress profiles for full coverage and partial covering platens were very similar (Fig. 1) to the stress profiles generated from the same disk with intact vertebral bone. The stress profiles showed uniform distribution of load over the entire diameter of the disk, even when only the central part was loaded. As expected, degenerate specimens showed an uneven load profile with regions of perturbation, when loaded with full coverage platens. Loading the degenerate disks with partially covering platens resulted in very uneven load profiles and in failure of the cartilaginous endplates at the higher load. Conclusion A critical step in the developme