Development and biological validation of a cyclic stretch culture system for the ex vivo engineering of tendons

Introduction: An innovative approach to the treatment of tendon injury or degeneration is given by engineered grafts, made available through the development of bioreactors that generate tendon tissue in vitro, by replicating in vivo conditions. This work aims at the design of a bioreactor capable of applying a stimulation of cyclic strain on cell constructs to promote the production of bioartificial tissue with mechanical and biochemical properties resembling those of the native tissue. Methods: The system was actuated by an electromagnet and design specifications were imposed as follows. The stimulation protocol provides to scaffolds a 3% preload, a 10% deformation, and a stimulation frequency rate set at 0.5, 1, and 2 Hz, which alternates stimulation/resting phases. Porcine tenocytes were seeded on collagen scaffolds and cultured in static or dynamic conditions for 7 and 14 days. Results: The culture medium temperature did not exceed 37°C during prolonged culture experiments. The applied force oscillates between 1.5 and 4.5 N. The cyclic stimulation of the engineered constructs let both the cells and the scaffold fibers align along the strain direction in response to the mechanical stimulus. Conclusion: We designed a pulsatile strain bioreactor for tendon tissue engineering. The in vitro characterization shows a preferential cell alignment at short time points. Prolonged culture time, however, seems to influence negatively on the survival of the cells indicating the need of further optimization concerning the culture conditions and the mechanical stimulation.