The effect of autologous mesenchymal stem cells on the biomechanics and histology of gel-collagen sponge constructs used for rabbit patellar tendon repair

The objective of this study was to introduce mesenchymal stem cells (MSCs) into a gel-sponge composite and examine the effect the cells have on repair biomechanics and histology 12 weeks postsurgery. We tested two related hypotheses - adding MSCs would significantly improve repair biomechanics and cellular organization, and would result in higher failure forces than peak in vivo patellar tendon ( PT) forces recorded for an inclined hopping activity. Autogenous tissue-engineered constructs were created by seeding MSCs from 15 adult rabbits at 0.1 x 10(6) cells/mL in 2.6 mg/mL of collagen gel in collagen sponges. Acellular constructs were created using the same concentration of collagen gel in matching collagen sponges. These cellular and acellular constructs were implanted in bilateral full-thickness, full-length defects in the central third of patellar tendons. At 12 weeks after surgery, repair tissues were assigned for biomechanical ( n = 12 pairs) and histological ( n = 3 pairs) analyses. Maximum force and maximum stress for the cellular repairs were about 60 and 50% of corresponding values for the normal central third of the PT, respectively. Likewise, linear stiffness and linear modulus for these cellular repairs averaged 75 and 30% of normal PT values, respectively. By contrast, the acellular repairs exhibited lower percentages of normal PT values for maximum force (40%), maximum stress (25%), linear stiffness ( 30%), and linear modulus (20%). Histologically, both repairs showed strong staining for collagen types III and V, fibronectin, and decorin. The cellular repairs also showed cellular alignment comparable to that of normal tendon. This study shows that introducing autogenous mesenchymal stem cells into a gel-collagen sponge composite significantly improves tendon repair compared to the use of a gel-sponge composite alone in the range of in vivo loading.