The use of functional tissue engineering and mesenchymal stem cell seeded constructs for patellar tendon repair

The objective of this study was to test the governing hypothesis that implanting mesenchymal stem cell (MSC)-seeded collagen gel and collagen sponge scaffolds into surgically induced rabbit patellar tendon (PT) defects will improve the repair tissues' structural and material properties as well as histological appearance.; We evaluated the effects of MSC-construct seeding concentration and collagen concentration on the in vivo repair quality after defect injury to the rabbit patellar tendon. In addition, we investigated the effects of adding a collagen sponge scaffold and mechanical stimulation using a silicone dish system on the in vivo repair of the rabbit patellar tendon. The effects of those treatments were assessed using biomechanical and immunohistochemical assays at 12 weeks post surgery.; No significant differences were found in the biomechanical properties of the cell-gel repairs with different MCS and collagen concentrations. The maximum force and linear stiffness for these repairs was 30% of normal central PT and no ectopic bone was found in any repair site. In a subsequent study, different collagen scaffolds (fibers, films, and sponges) were evaluated in vitro. We found that constructs prepared with cells, collagen gel and collagen sponge exhibited the greatest cell viability, penetration and mechanical integrity after 14 days in culture. In an attempt to increase the stiffness of the repairs, a type I collagen sponge was incorporated into the cell-gel constructs. The cell-gel-sponge repairs averaged 75% of the normal tendon linear stiffness and 60% of the normal tendon maximum force. In the next study, cell-gel-sponge constructs were mechanically stimulated and used for rabbit PT repair. Linear stiffness and linear modulus for the stimulated repairs averaged 80% and 40% of normal PT values, respectively. In the last study, cell-sponge constructs (using a different collagen sponge) were mechanically stimulated and used for rabbit PT repair. Linear stiffness and linear modulus for the stimulated repairs averaged 85% and 50% of normal PT values, respectively. Most important, the stimulated repairs produced tangent stiffnesses that were equivalent to normal PT in the range of in vivo forces recorded during inclined hopping (100 N) and 50% beyond this range (150 N).; The functional tissue engineering approach taken in this series of studies has made advances but faces new challenges. This approach has demonstrated the potential benefits of implanting MSC-seeded collagen scaffolds in treating tendon injuries. At the same time, these results suggest that more work must still be completed to optimize the MSC implant configuration and to improve the repair outcome in vivo. In the long term, tissue engineering should help to create more functional repairs that will enhance a patient's quality of life.