Background Implantation of the therapeutic depot is typical methods in tissue regeneration studies, but importantly, we developed an directional “releasing-to” approach by applying an adhesive gel patch (chitosan-catechol, CHI-C) on top of the fibrin gel, which plays a role in releasing the encapsulated PDGF-AA only to bone marrow direction for maximizing MSC cell migration. Furthermore, the migrated cells are retained on the defect site by the adhesive chitosan-catechol barrier.
Objectives The purpose of this study is to introduce the concept of the adhesive barrier/directional controlled release and prove its efficacy through an in vivo tracking model.
Methods 12 week-old male nude rats were anesthetized with zoletil and xylazine. A 1.5 mm outer diameter trephine drill was employed to create osteochondral defects (2.0×2.0 mm) in the trochlear groove of the femur. A hole was created inside the defect using a 26-gauge needle and deepened until blood gushed out. 1.0×106 MSCs suspended in 10 μl PBS was mixed with BD Matrigel of the same volume as described previously . The mixture was then slowly injected into the marrow cavity. And then, the osteochondral defects were filling with PDGF-AA-loaded HCF and sealed once more with CHI-C adhesive.
Results In vivo bioluminescence imaging was performed in transplanted animals for 14 days. In the HCF-only Group without PDGF-AA (Group 1), the majority of the injected MSCs remained in the marrow cavity for 7 days. On the other hand, Groups 2 (plugged with PDGF-AA-loaded HCF) and 3 (plugged with PDGF-AA and TGF-β1-loaded HCF) showed a time-dependent movement of injected cells toward the osteochondral defect. Interestingly, Group 4, in which osteochondral defects were sealed with CHI-C barrier, showed faster and greater movement of injected cells than other groups. Also, chemotactic potentials of Group 4 were maintained for 14 days while the cell migration was stopped within 7 days in other groups. On day 14, all the signals in Group 4 congregated at the osteochondral defect. After the animals were sacrificed at six week of transplantation, the femora were removed from the bodies and the far-red fluorescence signals were detected again. The fluorescent signals were detected in the osteochondral defect area in Groups 2, 3 and 4, whereas they were not detected in Group 1 (HCF-only Group). The total fluorescence signal in the femurs of Group 4 was 5.9-fold stronger than that of Group 1 (p<0.05), 2.7-fold stronger than that of Group 2 (p<0.05) and 2.5-fold stronger than that of Group 3 (p<0.05).
Conclusions We developed a novel system for osteochondral repair using directional bio-adhesive gel patch and growth factor-loaded HCF in which the CHI-C barrier induced a directional release of growth factors and blocked the dispersion of the migrated MSCs from the osteochondral bone region to other tissues. We confirmed that the CHI-C barrier enhanced the migration of MSCs to the osteochondral defect and induced better cartilage repair. This system is expected to make a significant contribution in cartilage tissue engineering without cell transplantation.
Lee JM, Kim BS, Lee H, Im GI. In vivo tracking of mesechymal stem cells using fluorescent nanoparticles in an osteochondral repair model. Mol Ther 2012:20:1434-42.
Acknowledgements This study was supported by a grant from the National Research Foundation of Korea (2009-0092196).
Disclosure of Interest None declared