Development of a bioreactor control system enabling combined mechanical and electrical stimulation for cardiac tissue engineering applications

Heart disease is the leading cause of death worldwide, representing a heavy social and economic burden globally. Cardiac fibrosis is involved in nearly all chronic cardiac pathologies, which gradually lead to cardiac remodelling and consequent heart failure. In this scenario, the development of reliable in vitro models replicating the human myocardial tissue and environment is of fundamental importance for studying cardiac physiopathology, as well as for testing the efficacy and toxicity of new drugs. Cardiac tissue engineering (CTE) aims to develop native-like cardiac tissues and one of the main points to achieve this is to provide adequate stimuli to undifferentiated cells. To achieve this goal, technological platforms called bioreactors, delivering controlled stimuli, are developed for accurately replicating the cardiac electro-mechanical environment. In this context, the work done in this MSc thesis concerned the design of a control system for a bioreactor for CTE. Based on the physiological conditions and the in vivo physical stimuli occurring in the cardiac tissue, the control system aims to provide mechanical and electrical stimuli with native-like amplitudes and timing. Starting from two existing devices previously developed for mechanical and electrical stimulation for CTE applications, the mechanical and electrical stimulation units were adapted for working simultaneously. The developed control unit was based on a BeagleBone Black microprocessor board, controllable through the Python programming language and dedicated existing libraries. The development process of the control algorithm followed four steps: 1) development of mechanical stimulation algorithm; 2) development of electrical stimulation algorithm; 3) development of user-friendly graphical interface; 4) combination of stimulation algorithms with the interface. The code for mechanical stimulation allows the operation of a stepper motor for the stretching of the tissue following a triangular or sinusoidal movement. The code for electrical stimulation allows the generation of square waves with several amplitudes and three waveforms: monophasic (positive or negative) and biphasic. For both stimulations, two protocols are available: the continuous mode, and the pulse mode, which alternates a period of stimulation with a period of break. The graphical user interface, comprising a screen and a keypad, allows navigating a menu displayed as a graphical window on the screen, choosing the type of stimulation, and successively, tuning all parameters. Experimental in-house tests were performed to evaluate the accuracy and reliability of the developed system. For the imposed motor displacement values (0.25 - 3 mm), both sinusoidal and triangular motions were delivered with a shape compatible with the ideal waveform and the mean error values between the measured amplitude values and the nominal ones were always lower than 5 %. The electrical pulses were delivered with accurate pulse duration, amplitudes, and frequencies. The parallelization of stimulations was successful. However, the high computing resources suggested the use of a more powerful board for future works, above all for the stimulation of several constructs simultaneously. The developed system, further optimized and combined with an adapted culture chamber, would constitute a powerful research platform for performing basic and translational research on cardiac physiopathology and drug discovery.