Correlation between the nano-structure and macro-mechanics of human nucleus pulposus

Abstract

Collagen fibrils are the main structural components of the intervertebral discs. The role played by the morphology of collagen fibrils in maintaining the mechanical integrity of the nucleus pulposus is not clear. This study aimed at quantifying the diameter of the individual collagen fibrils of the nucleus pulposus and evaluating its correlation with the bulk mechanical properties of the nucleus pulposus. Collagen fibrils were extracted from the nucleus pulposus of discs (n=7) retrieved from adolescents during scoliosis correction surgery and the extracts were confirmed by SDS-PAGE. The diameter of the individual collagen fibrils were measured through Atomic Force Microscope imaging and the compressive mechanical properties of the tissues were evaluated by confined compression. The correlations between the morphology of the collagen fibrils and the mechanical properties of the tissues were evaluated. The SDSPAGE results showed that the collagen extracts were composed of collagen II. The mean diameter of the collagen fibrils was 92.09±26.5 nm; the mean swelling pressure and compressive modulus of the tissues were 6.15±4.3 KPa and 1.23±0.7 MPa respectively. The mean fibril diameter had no linear correlation (R^2 =0. 295) with the swelling pressure of the tissues. However, it had a significant linear correlation with the compressive modulus (p=0.023, R^2=0.676). This is the first study, to our knowledge, to evaluate the nano-scale properties of the individual collagen fibrils of the disc and their relationship with macro-scale mechanical properties of the disc tissues.