A Regenerative Medicine Approach to Improved Tendon Healing and Repair

Surgical repair of torn tendons is a common orthopaedic procedure in the United States, with nearly 400,000 repairs occurring annually. Despite improvements in surgical techniques used to re-attach the tendon to its boney insertion, clinically successful outcomes amongst patients are variable and re-tear rates can be exceedingly high. The use of stem cells as an adjunct to surgical repair to aid in improving tendon healing and repair strength has gained much interest amongst the clinical community. Accordingly, many investigators have begun examining the ability of stem cells to differentiate into tenocytes using various methodologies including the application of growth factors and mechanical cues. We hypothesized that the differentiation of adipose derived stem cells (ADSCs) into tenocytes could be achieved via the application of soluble BMP-12, a growth factor believed to be involved in tenogenesis and which has exhibited the ability to induce neo-tendon formation following ectopic delivery in rats. Furthermore, we believed that the application of cyclic tensile strain, in addition to the application of BMP-12, would enhance tenogenic differentiation. First, based on this hypothesis, we performed in vitro studies to determine the ideal differentiation conditions to obtain a tenocytes-like phenotype. Because there is no one specific marker for tenocytes, an array of markers was used to capture the profile of a tenocytes, which includes scleraxis, tenomodulin, collagen I and collagen III. Results showed increased tenocytes-like phenotype in ADSCs differentiated statically for 7 days on monolayer. Using these results, an animal study was performed on the Achilles tendon of male Lewis rats (n=60) to determine the effects of BMP-12 differentiated ADSCs on injured tendons. ADSCs were either differentiated with BMP-12 or cultured in control medium at the optimal conditions and then seeded onto Conexa scaffolds for three days. At the three day mark, surgeons from the Steadman Hawkins Clinic of the Carolinas induced a window transection in the Achilles tendon approximately 2mm x 6 mm and mended the injury with a scaffold either seeded with no cells (n=20), undifferentiated ADSCs (n=20), or BMP-12 differentiated stem cells (n=20). The healthy, contralateral leg was used as a positive control. The animals were sacrificed at 7 weeks and the injured Achilles tendons were acquired for molecular (n=6), histological (n=4), and mechanical analysis (n=10). The same procedure and analyses were performed on the contralateral tendons. Results show that autologous cell-seeded scaffolds are good candidates for repair of tendon injuries