The effect of biomimetic electromechanical stimulation on the development and function of engineered myocardial tissue

Heart failure is one of the leading causes of death in the United States and is becoming one of the leading causes of death worldwide. A myocardial infarction can lead to heart failure as the heart remodels itself to compensate for the lost contractile tissue. Though heart transplantation is the gold standard of care, limited organ availability and the need for lifelong immunosuppressant drugs means that innovative treatment methods are required to fulfill the growing need. Tissue engineered myocardium aims to repair or replace damaged tissue by matching the electromechanical function of the native heart.;Though extensive studies have investigated the development of engineered myocardium, current state-of-the-art methods do not generate constructs that are able to match the function of native tissue. In this work, we investigated the use of biomimetic stimulation on the development and function of engineered myocardium by creating a dual electromechanical bioreactor that allows us to control the timing of stimulation on a cycle-to-cycle basis. With this bioreactor system, we present evidence that although introduction of frequency variability of mechanical stimulation has a limited effect on the resulting twitch force of the constructs, it has a significant effect on cell-cell coupling and growth pathway activation in constructs. We also demonstrated that electrical and mechanical stimulation alone have similar effects on the resulting twitch force, though the mechanical stimulation improvements are likely due to increases in cell number, while electrical stimulation improvements are likely due to increases in cell-cell coupling. Constructs cultured under delayed electromechanical stimulation, which models the period of isovolumic contraction present in the cardiac cycle, had the highest twitch forces, likely due to an increase in contractility proteins (Troponin I), and calcium handling proteins (SERCA2a), which were in turn the result of increases in physiological hypertrophic pathway proteins (Akt). Furthermore, when the electrical and mechanical stimulations are completely offset to model non-physiological conditions, we saw a reduction in twitch force generation of the constructs indicating that the timing of dual electromechanical stimulation is important in generating optimal construct function. Our system can be easily modified to change the isovolumic contraction time (ICT), which changes during both normal developmental processes and following disease, allowing for the potential to study many cardiovascular diseases in vitro. A preliminary in vivo study aimed at quantifying the efficacy of construct implantation following a myocardial infarction in rats indicated that our constructs transiently improved fractional shortening by ∼15%. Furthermore, histological staining indicated that our constructs maintained cell viability with both cardiomyocytes and fibroblasts present, even 10 weeks post-implantation.