TNF and Intervertebral disk degeneration: To evaluate the effects of mechanical stretching stress on NP cells, we stretched NP cells with different values (0-6000μ) for 12 or 24 h, and monitored the cell viability, the production of TNF-α, an inflammatory cytokine associated with intervertebral disc degeneration, the expression of NP cells marker aggrecan and disc degenerative marker MMP-3.