Study Design. A combined experimental and theoretical biomechanical study to quantify the mechanical properties of living cells of the porcine intervertebral disc.
Objectives. To quantify zonal variations in the mechanical properties and morphology of cells isolated from the intervertebral disc.
Summary of Background Data. Cellular response to mechanical stimuli is influenced by the mechanical properties of cells and of the extracellular matrix. Significant zonal variations in intervertebral disc matrix properties have been reported. No information is currently available on the corresponding regional variations in the mechanical properties of intervertebral disc cells, despite evidence of significant differences in cellular phenotype and biologic response to loading.
Methods. The micropipette aspiration test was used in combination with a three-parameter viscoelastic solid model to measure the mechanical properties of cells isolated from the anulus fibrosus, transition zone, and nucleus pulposus.
Results. Intervertebral disc cells exhibited viscoelastic solid behaviors. Highly significant differences were observed in the morphology, cytoskeletal arrangement, and biomechanical properties of the nucleus pulposus cells as compared with anulus fibrosus or transition zone cells. Cells of the nucleus pulposus were approximately three times stiffer and significantly more viscous than cells of the anulus fibrosus or transition zone.
Conclusions. The findings of this study provide new evidence for the existence of two biomechanically distinct cell populations in the intervertebral disc. These differences in mechanical behavior may be related to observed differences in the cytoskeletal architecture between these cells, and may further play an important role in the development, maintenance, and degeneration of the intervertebral disc.
From the Departments of *Surgery, †Biomedical Engineering, and ‡Mechanical Engineering & Materials Science, Duke University Medical Center, Durham, North Carolina.
Supported by NIH grants AR43876 and AG15768, NSF PECASE (BES-9703299), and fellowships from the NIH, Whitaker Foundation, and NSF.
Address reprint requests to
Farshid Guilak, PhD
Orthopaedic Research Laboratories
Duke University Medical Center
375 Medical Sciences Research Building
Research Drive, Box 3093
Durham, NC 27710