Human Flexor Tendon Tissue Engineering: In Vivo Effects of Stem Cell Reseeding

Background: Tissue-engineered human flexor tendons may be an option to aid in reconstruction of complex upper extremity injuries with significant tendon loss. The authors hypothesize that human adipose-derived stem cells remain viable following reseeding on human tendon scaffolds in vivo and aid in graft integration. Methods: Decellularized human flexor tendons harvested from fresh-frozen cadavers and reseeded with green fluorescent protein-labeled pooled human adipose-derived stem cells were examined with bioluminescent imaging and immunohistochemistry. Reseeded repaired tendons were compared biomechanically with unseeded controls following implantation in athymic rats at 2 and 4 weeks. The ratio of collagen I to collagen III at the repair site was examined using Sirius red staining. To confirm cell migration, reseeded and unseeded tendons were placed either in contact or with a 1-mm gap for 12 days. Green fluorescent protein signal was then detected. Results: Following reseeding, viable cells were visualized at 12 days in vitro and 4 weeks in vivo. Biomechanical testing revealed no significant difference in ultimate load to failure and 2-mm gap force. Histologic evaluation showed host cell invasion and proliferation of the repair sites. No increase in collagen III was noted in reseeded constructs. Cell migration was confirmed from reseeded constructs to unseeded tendon scaffolds with tendon contact. Conclusions: Human adipose-derived stem cells reseeded onto decellularized allograft scaffolds are viable over 4 weeks in vivo. The movement of host cells into the scaffold and movement of adipose-derived stem cells along and into the scaffold suggests biointegration of the allograft.