Copyright © 2017 American Society of Plastic Surgeons. Unauthorized reproduction of this article is prohibited. www.PRSJournal.com 1305e T issue engineering of fexor tendons addresses a challenge often faced by hand surgeons: a limited supply of donor ten- dons. 1 Decellularized human cadaveric tendon allografts are a potential source for use in tendon reconstruction. Reseeding these biostatic ten- don scaffolds ex vivo with recipient cells before implantation, a process termed revitalization, has demonstrated several advantages. 2,3 First, adipose-derived stem cells used for reseeding have been shown to retain their metabolic activ- ity, synthesize collagen, and stimulate intrinsic tendon healing by initiating the repair process. 4,5 Second, revitalized grafts have been shown to undergo remodeling and incorporation into the host tissue faster, 6,7 thus decreasing the risk for foreign body reaction to unincorporated tendon grafts. Finally, revitalization has been shown to Disclosure: None of the authors has a financial in- terest in any of the products or devices mentioned in this article. Copyright © 2017 by the American Society of Plastic Surgeons DOI: 10.1097/PRS.0000000000003359 Chao Long, A.B. Michael G. Galvez, M.D. Anais Legrand, M.D. Lydia-Marie Joubert, Ph.D. Zhen Wang, M.D. Arhana Chattopadhyay, B.A. James Chang, M.D. Paige M. Fox, M.D., Ph.D. Stanford and Palo Alto, Calif. Background: Decellularized cadaveric tendons are a potential source for recon- struction. Reseeding to enhance healing is ideal; however, cells placed on the tendon surface result in inadequate delivery. The authors used an injection technique to evaluate intratendinous cell delivery. Methods: Decellularized tendons were reseeded with adipose-derived stem cells in culture, and injected with fetal bovine serum or hydrogel. PKH26- stained cells in cross-section were quantifed. To evaluate cell viability, the authors delivered luciferase-labeled cells and performed bioluminescent imaging. To evaluate synthetic ability, the authors performed immunohis- tochemistry of procollagen. Adipose-derived stem cells’ ability to attract tenocytes was assessed using transwell inserts. Cell-to-cell interaction was assessed by co-culturing, measuring proliferation and collagen production, and quantifying synergy. Finally, tensile strength was tested. Results: Both fetal bovine serum (p < 0.001) and hydrogel (p < 0.001) injec- tion led to more cells inside the tendon compared with culturing. Hydrogel injection initially demonstrated greater bioluminescence than culturing (p < 0.005) and fetal bovine serum injection (p < 0.05). Injection groups dem- onstrated intratendinous procollagen staining correlating with the cells’ lo- cation. Co-culture led to greater tenocyte migration (p < 0.05). Interaction index of proliferation and collagen production assays were greater than 1 for all co-culture ratios, demonstrating synergistic proliferation and collagen production compared with controls (p < 0.05). There were no differences in tensile strength. Conclusions: Hydrogel injection demonstrated the greatest intratendinous seeding effciency and consistency, without compromising tensile strength. Intratendinous cells demonstrated synthetic capabilities and can potentially attract tenocytes inside the tendon, where synergy would promote intrinsic tendon healing. (Plast. Reconstr. Surg. 139: 1305e, 2017.) CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V. From the Cell Sciences Imaging Facility, Stanford Univer- sity School of Medicine; the Division of Plastic and Recon- structive Surgery, Stanford Health Care; and the Division of Plastic and Reconstructive Surgery, Veterans Affairs Palo Alto Health Care System. Received for publication June 9, 2016; accepted November 8, 2016. Intratendinous Injection of Hydrogel for Reseeding Decellularized Human Flexor Tendons HAND/PERIPHERAL NERVE