PURPOSE: In cases of mutilating hand injuries, large amounts of tendon grafts may be needed for reconstruction. Tissue engineered flexor tendons may address this need. In this study, we examined the effect of a tissue bioreactor on the biomechanical properties of reseeded flexor tendon constructs.
MATERIAL AND METHODS: Flexor tendons were harvested from the rear paw of New Zealand white rabbits. The tendons were acellularized and seeded with either adipoderived stem cells (ASC) or fibroblasts (F) (2 x 106 per construct). A custom bioreactor (Ligagen L30-4C, DynaGen systems, Tissue Growth Technologies, Minnetonka, MN) was used to apply a cyclic mechanical load (1cycle/min) onto the tendon constructs with a stretch force of 1.25 N over five days. Two additional groups were used as controls for each type of cell – seeded construct: Fresh tendons (n = 15) and acellularized tendons that were seeded with either ASCs or F and then incubated for 5 days (without stretch, unloaded control tendons,). Comparison across groups was assessed using one - way ANOVA followed by pairwise comparisons of means using the Schéffe test with the significance level set at p < 0.05.
RESULTS: We compared the ultimate tensile stress (UTS) and the elastic modulus (EM) of the bioreactor - treated tendons to the unloaded control tendons and the fresh control tendons. UTS and EM values of bioreactor - treated tendons that were exposed to cyclic load (+) were significantly higher than those of unloaded control tendons (-) [UTS(ASC+) 66.74 MPa vs UTS(ASC-) 47.90 MPa, UTS(f+) 69.73 MPa vs UTS(f-) 45.03 MPa and EM(ASC+) 906.68 MPa vs EM(ASC-) 715.57 MPa, EM(f+) 940.99 MPa vs EM(f-) 678.32 MPa, p(UTS) < 0.0001 and p(EM) < 0.0001]. The bioreactor - treated tendons approached the values of UTS and EM of fresh tendons [UTS(fresh) 63.15 MPa, EM(fresh) 974.54 MPa]. Histologically, cyclic strain caused the cells and their actin cytoskeleton to reorient themselves parallel to the direction of strain.
CONCLUSION: The application of cyclic strain on seeded tendon constructs improved their biomechanical properties, achieving values comparable to fresh intact tendons. The bioreactor may therefore contribute to the in vitro production of strong tendon material that could have clinical applications in hand reconstruction.