A Bioreactor for Controlled Electrical and Mechanical Stimulation of Developing Scaffold-Free Constructs

Bioreactors are commonly used to apply biophysically relevant stimulations to tissue-engineered constructs in order to explore how these stimuli influence tissue development, healing, and homeostasis, and they offer great flexibility because key features of the stimuli (e.g., duty cycle, frequency, amplitude, and duration) can be controlled to elicit a desired cellular response. However, most bioreactors that apply mechanical and electrical stimulations do so to a scaffold after the construct has developed, preventing study of the influence these stimuli have on early construct development. To enable such exploration, there is a need for a bioreactor that allows the direct application of mechanical and electrical stimulation to constructs as they develop. Herein, we develop and calibrate a bioreactor, based on our previously established modified Flexcell system, to deliver precise mechanical and electrical stimulation, either independently or in combination, to developing scaffold-free tissue constructs. Linear calibration curves were established, then used to apply precise dynamic mechanical and electrical stimulations, over a range of physiologically relevant strains (0.50%, 0.70%, 0.75%, 1.0%, and 1.5%) and voltages (1.5 and 3.5 V), respectively. Following calibration, applied mechanical and electrical stimulations were not statistically different from their desired target values and were consistent whether delivered independently or in combination. Concurrent delivery of mechanical and electrical stimulation resulted in a negligible change in mechanical (<2%) and electrical (<1%) values, compared to their independently delivered values. With this calibrated bioreactor, we can apply precise, controlled, reproducible mechanical and electrical stimulations, alone or in combination, to scaffold-free, tissue-engineered constructs as they develop.