Modulation of annulus fibrosus cell alignment and function on oriented nanofibrous polyurethane scaffolds under tension

Background contextAnnulus fibrosus (AF), a component of the intervertebral disc (IVD), is always under tension in vivo, a condition that must be taken into consideration when tissue engineering an IVD. Loss of the tensile forces has been implicated in the pathogenesis of disc degeneration characterized by mechanical and structural breakdown of the AF.PurposeIn this study, we hypothesize that tensile forces modulate cellular and molecular behavior of AF cells grown on nanofibrous scaffolds in vitro.Study design/settingBovine AF cells were seeded onto strained electrospun-aligned nanofibrous polycarbonate urethane (PU) scaffolds. Tension was either maintained throughout the culture duration (monotonic) or removed after 24 hours (relaxed).MethodsThe effect of tension on AF cells cultured on PU scaffolds was evaluated over 7 days by scanning electron microscopy, biochemical assays, immunofluorescence microscopy, and quantitative polymerase chain reaction.ResultsCells grown on the relaxed scaffold were significantly more proliferative, synthesized more collagen and had increased collagen type I and TGFβ-1 gene expression; however these cells were not as aligned as were the cells and matrix on monotonic strained scaffolds. The alignment of AF cells grown on monotonic scaffolds correlated with significantly greater scaffold elastic modulus on day 7. Additionally, the cellular response to the change in strain was delayed by 3 to 5 days after tension release, which correlated with the time at which changes in scaffold length were detected.ConclusionsThis study demonstrated that AF cells respond at the molecular and cellular level to the changes in matrix/scaffold tension. This suggests that it may be necessary to determine the optimal elastic modulus and applied tensile forces to tissue engineer an AF that mimics the native tissue. Furthermore, this study provides insight into how changes in tensile forces may lead to changes in the AF cell function.