Effects of Radial Compression on a Novel Simulated Intervertebral Disc–Like Assembly Using Bone Marrow–Derived Mesenchymal Stem Cell Cell-Sheets for Annulus Fibrosus Regeneration

STUDY DESIGN: The aim of this study was to develop a tissue engineering approach in regenerating the annulus fibrosus (AF) as part of an overall strategy to produce a tissue-engineered intervertebral disc (IVD) replacement. OBJECTIVE: To determine whether a rehabilitative simulation regime on bone marrow–derived mesenchymal stem cell cell-sheet is able to aid the regeneration of the AF. SUMMARY OF BACKGROUND DATA: No previous study has used bone marrow–derived mesenchymal stem cell cell-sheets simulated by a rehabilitative regime to regenerate the AF. METHODS: The approach was to use bone marrow–derived stem cells to form cell-sheets and incorporating them onto silk scaffolds to simulate the native lamellae of the AF. The in vitro experimental model used to study the efficacy of such a system was made up of the tissue engineering AF construct wrapped around a silicone disc to form a simulated IVD-like assembly. The assembly was cultured within a custom-designed bioreactor that provided a compressive mechanical stimulation onto the silicone disc. The silicone nucleus pulposus would bulge radially and compress the simulated AF to mimic the physiological conditions. The simulated IVD-like assembly was compressed using a rehabilitative regime that lasted for 4 weeks at 0.25 Hz, for 15 minutes each day. RESULTS: With the rehabilitative regime, the cell-sheets remained viable but showed a decrease in cell numbers and viability. Gene expression analysis showed significant upregulation of IVD-related genes and there was an increased ratio of collagen type II to collagen type I found within the extracellular matrix. CONCLUSION: The results suggested that a rehabilitative regime caused extensive remodeling to take place within the simulated IVD-like assembly, producing extracellular matrix similar to that found in the inner AF.