Investigation into the effects of varying frequency of mechanical stimulation in a cycle-by-cycle manner on engineered cardiac construct function

Abstract

Mechanical stimulation has been used extensively to improve the function of cardiac engineered tissue, as it mimics the physical environment in which the tissue is situated during normal development. However, previous mechanical stimulation has been carried out under a constant frequency that more closely resembles a diseased heart. The goal of this study was to create a bioreactor system that would allow us to control the mechanical stimulation of engineered cardiac tissue on a cycle-by-cycle basis. This unique system allows us to determine the effects on cardiac construct function of introducing variability to the mechanical stretch. To test our bioreactor system, constructs created from neonatal rat cardiomyocytes entrapped in fibrin hydrogels were stimulated under various regimes for 2 weeks and then assessed for functional outcomes. No differences were observed in the final cell number in each condition, indicating that variability in frequency did not have a negative effect on viability. The forces were higher for all mechanical stimulation groups compared to static controls, although no differences were observed between the mechanically stimulated conditions, indicating that variable frequency on a cycle-by-cycle basis has limited effects on the resulting force. Although differences in the observed twitch force were not observed, differences in the protein expression indicate that variable-frequency mechanical stimulation had an effect on cell-cell coupling and growth pathway activation in the constructs. Thus, this bioreactor system provides a valuable tool for further development and optimization of engineered myocardial tissue as a repair or replacement strategy for patients undergoing heart failure. Copyright © 2014 John Wiley & Sons, Ltd.

Anisotropic engineered heart tissue made from laser-cut decellularized myocardium

“…The only other study to report both TTP and RT50 in NRVM based 2 week old EHTs was the work of Morgan et al 53. Their reported RT50 and TTP values (125 and 150 ms respectively at 0.5 Hz pacing)53 are notably slower than those observed in our method. This difference could potentially be explained by our T3 media substitution54.…”

Electrical and mechanical stimulation of cardiac cells and tissue constructs

“…Isolated neonatal CMs cultured in a dynamic bio-reactor were used to evaluate variable frequency of mechanical stimulation in a cycle-by-cycle manner (see the mechanical descriptions in Fig. 4E) [313]. Gaussian stimulation may promote physiological over pathological hypertrophy as shown by lower ratios phosphorylated ERK1/2 to ERK1/2.…”

“…The design of the reactor control system enables the development of electrical and mechanical stimulation regimes that can mimic both healthy function (isovolumic contraction) as well as characteristic changes in disease. Control of stimulation regimes also enables the integration of construct “exercise” to replicate changes in heart rate [33,34,313,383]. …”

Establishing Early Functional Perfusion and Structure in Tissue Engineered Cardiac Constructs

“…Morgan et al 174–177 further pointed out that the combined electrical and mechanical stimulations are necessary for improved functional properties plus the timing of the combined stimulation also greatly affect the engineered cardiac tissue. Moreover, a very interesting phenomenon was observed by Morgan et al 174,175 ; they found that, when the electrical stimulus was slightly delayed after the beginning of mechanical stimulus, the yield constructs had improved function and better expression of proteins responsible for cell–cell communication and contractility.…”

“…Hence, one subtle mimicking of the biophysical environment during isovolumic contraction is able to improve quality of the cardiac construct, implying that bioreactor design and the conditioning regimen planning should more accurately reproduce in vivo physiological conditions. 174–177 …”