Perspectives on cell and collagen composites for tendon repair

Cell and matrix composites recently have been used to repair tendons and li gaments. In the current study the authors briefly review prior studies in t his area, and the contributions these findings have made toward solving thi s clinical problem. The authors then provide a perspective on the necessary characteristics that the cells and delivery vehicles of these composites m ust possess, separately and in combination, to function successfully after surgery. The authors conclude by applying these functional tisue engineerin g principles to two tendon injury models in which mesenchymal stem cells ha ve been suspended in Type I collagen gel to form composites for patellar an d Achilles tendon repair. In the first study, mesenchymal stem cells were s uspended in gel (5 million cells/mL) with no attempt to align the cells dur ing incubation. The resulting composites were implanted in window defects i n one patellar tendon in the rabbit knee, with gel alone in a matching defe ct on the contralateral side. Biomechanical evaluation at 4 weeks showed th at the material properties of the mesenchy-mal stem cell based repairs were 18% to 33% greater than results for contralateral controls. In the second study, mesenchymal stem cells were suspended in gel (4 million cells/mL), c ontracted on a tensioned suture during incubation, placed in an Achilles ga p defect, and compared,vith repairs of contralateral gap injuries containin g suture alone (controls), By 4 weeks, the repairs treated 7 with mesenchym al stem cells had achieved twice the structural properties of the contralat eral controls and 50% to 60% of the stiffness and strength of normal tendon s that were not surgically treated. In addition, the material properties of the repairs treated with. mesenchymal stem cells had increased with time t o 37% of normal by 12 weeks after surgery. Both studies reveal the benefits of using pluripotential cells in a collagen gel matrix, and suggest additi onal research that might enhance the repair quality of healing tendons.