There is significant clinical demand for functional tendon grafts in human and veterinary medicine. Tissue engineering techniques combining cells, scaffolds and environmental stimuli may circumvent the shortcomings of traditional transplantation processes. In this study, the influence of cyclic mechanical stimulation on graft maturation and cellular phenotype was assessed in an equine model. Decellularized tendon scaffolds from four equine sources were seeded with syngeneic bone marrow-derived mesenchymal stem cells and subjected to 0%, 3% or 5% strain at 0.33Hz for up to one hour daily for 11 days. Cells cultured at 3% strain integrated deep into their scaffolds, altered extracellular matrix composition, adopted tendon-like gene expression profiles, and increased construct elastic modulus and ultimate tensile strength to native levels. This bioreactor protocol is therefore suitable for cultivating replacement tendon material or as an in vitro model for studying differentiation of stem cells toward tendon.

Adult tissue stem cells have shown promise for the treatment of debilitating tendon injuries. However, few comparisons of stem cells from different tissue sources have been made to determine the optimum stem cell source for treating tendon. Moreover, it is likely that the application of tenogenic growth factors will improve tendon stem cell treatments further, and a comprehensive comparison of a number of growth factors is needed. Thus far, different types of stem cells cannot be evaluated in a high-throughput manner. To this end, we have developed an approach to culture mesenchymal stem cells isolated from bone marrow in collagen type I hydrogels with tenogenic growth factors using economical, commercially available supplies. To optimize growth factors for this assay, FGF-2, TGF-β1, IGF-1, and/or BMP-12 were tested singly and in novel combinations of (1) BMP-12 and IGF-1, (2) TGF-β1 and IGF-1, and/or (3) BMP-12 and FGF-2 over 10 days. Our data suggest that BMP-12 supplementation alone results in the strongest expression of tendon marker genes, controlled contractility of constructs, a higher degree of cell alignment, and tendon-like tissue morphology. This easy-to-use benchtop assay can be used to screen novel sources of stem cells and cell lines for tissue engineering and tendon healing applications.