Purpose: Mutilating injuries of the hand and upper extremity result in tendon losses too great to be replaced by autologous grafts. Our goal is to use tissue engineering techniques to produce additional tendon material. In this study, we used a custom bioreactor to apply cyclic mechanical loading onto tissue engineered tendon constructs to study viability and ultimate tensile stress.
Methods: A custom LigaGen tissue bioreactor providing uniaxial tendon strain (DynaGen systems) was used for this study. Tendon constructs were subjected to a stretch force of 5N, exposing each construct to 1.25N over a 5 day course (n = 4). Constructs used were acellularized tendons reseeded with tenocytes or left unseeded. Actual tendon strain was measured linearly by comparing resting tendon length to tendon length under applied tension. Ultimate tensile stress and elastic modulus of the tendon constructs were compared after different cycle parameters (1cycle/min vs. 2cycles/min in alternating 1 hour periods of loading and rest) using a materials testing system (MTS 858, MTS Inc). Histologic appearances were examined for tendon architecture with specific emphasis on collagen organization. Finally, pairwise comparison of means across groups was assessed using the two-tailed unpaired Student T-test with the significance level set at p < 0.05.
Results & Conclusions: Seeded tendon constructs that were exposed to a 1 cycle/min load were found to have a significantly increased ultimate tensile stress and elastic modulus (UTS = 84.73N; λ = 1054.77MPa) compared to non-loaded controls (UTS = 38.90N, p = 0.002; λ = 699.98MPa, p = 0.03). Seeded tendon constructs exposed a 2 cycle/min load also had a significant yet less remarkable increase (UTS = 73.95N; λ = 1045.21MPa) compared to non-loaded controls (UTS = 38.90N, p = 0.01; λ = 699.98MPa, p = 0.02). Histologically, stressed tendons showed better alignment of collagen fibrils.
Relevance: This study shows that cyclic loading of tendon constructs increases the strength of seeded constructs and changes the constructs’ collagen architecture. The use of the bioreactor may therefore accelerate the in vitro production of strong, non-immunogenic tendon material that can potentially be used clinically to reconstruct significant tendon losses. The ultimate goal of this project is to produce tissue engineered tendon for clinical use in hand and upper extremity reconstruction.