Viscoelastic Properties Of Normal And Degenerative Nucleus Pulposus Cells In Vitro

Objectives:To quantify the biomechanical properties of human normal and degenerative nucleus pulposus(NP) cells in vitro.Method: The normal nucleus pulposus cells obtained from discarded NP tissue of 3 scoliosis patients aged from 13 to 16 years,and the degenerative nucleus pulposus cells obtained from discarded NP tissue of 3 protrusion of the lumbar intervertebral disc patients. Pancreatin and collagenase type II were used to digest NP and cells were isolated from NP. Type II collagen immunofluorescence and Fan seaing were used to identify NP cells. The micropipette aspiration test combined with Half-space model was used to measure the mechanical properties of NP cells.Results: In the morphologic properties,the degenerative NP cells showed a greater range of sizes, and their average diameter (17.29±2.76μm) was significantly greater than the normal ones (15.07±1.62μm).Upon the same negative pressure, the equilibrium modulus(E∞), the instantaneous modulus (E0) and the viscosity (μ) between the normal NP cells and the degenerative ones had no significant statistical differences (P≥0.05).Conclusion: Both the normal and degenerative nucleus pulposus cells performance as a typical viscolastic solid creep. The viscoelastic properties have no significant difference between the normal and degenerative nucleus pulposus cells.