Nano Structure and Biomechanics of Human Intervertebral Disc Collagens

Abstract

Introduction. Degenerative disc disease is a primary cause of sciatica and low back pain in young individuals. Researchers are working on developing tissue engineered disc replacements to treat degenerated discs, with no significant clinical outcome yet. Collagen fibrils are the basic structural components of disc tissues, therefore it is essential to study these structures individually. The aim of this study was to quantify the morphology and mechanical properties of human intervertebral disc collagens. Methods. Disc samples showing no evidence of degeneration were harvested from young patients during scoliosis surgery. Collagen II containing fibrils were extracted from the nucleus pulposus of these discs by homogenization and high speed centrifugation in the presence of protease inhibitors. Collagen protein expression of the resulting pellets was evaluated by western blot technique. The extracts were imaged in dry condition under the Atomic Force Microscope (AFM) to study the fibril morphology. The fibrils were then mechanically tested in phosphate buffered saline medium by stretching them individually in the force spectroscopy mode of AFM. The force-elongation profiles from the force spectroscopy experiments were plotted. Results. The extracts were biochemically confirmed to contain pure collagen II. The length of the collagen fibrils ranged from 1 – 10 m, with an average diameter of 98.9 34.3 nm. The 67 nm characteristic banding pattern of collagens was observed in these fibrils. The Young’s modulus of the fibrils was found to be 0.12 0.06 MPa from the force spectroscopy study. Discussion. We further plan to use discs from cadavers to compare and correlate the mechanical properties of collagen fibrils (I & II) with the degree of disc degeneration. The data obtained from this study will be a rich source of information to understand the pathophysiology of the degenerative disc disease and will eventually lead to development of better treatment methods.