Functional tissue engineering for tendon repair: A multidisciplinary strategy using mesenchymal stem cells, bioscaffolds, and mechanical stimulation.

Over the past 8 years, our group has been continuously improving tendon repair using a functional tissue engineering (FTE) paradigm. This paradigm was motivated by inconsistent clinical results after tendon repair and reconstruction, and the modest biomechanical improvements we observed after repair of rabbit central patellar tendon defects using mesenchymal stem cell-gel-suture constructs. Although possessing a significantly higher stiffness and failure force than for natural healing, these first generation constructs were quite weak compared to normal tendon. Fundamental to the new FTE paradigm was the need to determine in vivo forces to which the repair tissue might be exposed. We first recorded these force patterns in two normal tendon models and then compared these peak forces to those for repairs of central defects in the rabbit patellar tendon model (PT). Replacing the suture with end-posts in culture and lowering the mesenchymal stem cell (MSC) concentration of these constructs resulted in failure forces greater than peak in vivo forces that were measured for all the studied activities. Augmenting the gel with a type I collagen sponge further increased repair stiffness and maximum force, and resulted in the repair tangent stiffness matching normal stiffness up to peak in vivo forces. Mechanically stimulating these constructs in bioreactors further enhanced repair biomechanics compared to normal. We are now optimizing components of the mechanical signal that is delivered in culture to further improve construct and repair outcome. Our contributions in the area of tendon functional tissue engineering have the potential to create functional load-bearing repairs that will revolutionize surgical reconstruction after tendon and ligament injury. (c) 2007 Orthopaedic Research Society.