Tissue engineered intrasynovial tendons: in vivo graft survival and tensile strength

Rabbit flexor tendons can be harvested, acellularized, and used as scaffolds for reseeding of flexor tendon constructs. The purpose of this study was to compare the biomechanical characteristics of seeded and unseeded flexor tendon constructs to autologous grafts in vivo in the rabbit model. The experimental groups were created using acellularized rabbit tendon scaffolds: scaffolds with no cells, and scaffolds re-seeded with either tenocytes or adipoderived stem cells. Autologous flexor tendon grafts were used as controls. All constructs bridged a zone II defect in the rabbit and were explanted at 2, 4, 10, or 20 weeks. These tendons were then tested for ultimate tensile strength (UTS) or processed for histology. The experimental groups exhibited UTS comparable to autologous grafts up to 4 weeks, and were significantly weaker at 10 weeks (p < 0.000–0.024). At 20 weeks, UTS was significantly improved (p = 0.013) in tenocyte-seeded constructs compared with 10 weeks. There was no significant difference in UTS between seeded or unseeded constructs at 2, 4, and 20 weeks. In all groups, there were more cells at the repair ends, and the cells penetrated to the core of the grafts over time. The goal of this technology is the development of tissue engineered tendon grafts for clinical use. This study provides proof of the concept that tissue-engineered flexor tendons—both acellularized and reseeded—can survive and incorporate over time. Further work will focus on bioreactor preconditioning of reseeded constructs to increase ultimate tensile strength.