An Engineered Myocardial Infarct Border‐Zone‐on‐a‐Chip Demonstrates an Oxygen Gradient Alters Cardiomyocyte Calcium Handling.

R2883 --> Introduction: During most cases of myocardial infarction (MI), an atherosclerotic plaque occludes a coronary artery, thereby obstructing the flow of blood and oxygen (O2) to the myocardial tissue. A localized site of hypoxia develops with subsequent massive cardiomyocyte (CM) cell death. As a result of the distorted cardiac blood supply, steep O2 gradients develop at the MI border zone region between the injured, hypoxic myocardial tissue and the surrounding viable, normoxic myocardial tissue. Although the border zone is understood to be a transition region in electromechanical properties of CMs, little is known about the effect of O2 gradients on the function of human myocardial tissue, including the effect of hypoxic CMs on nearby normoxic CMs and vice versa. The objective of this study was to engineer an O2 landscape microphysiological system to expose CMs to O2 gradients that mimic an MI border zone and study its effect on CM calcium transients and calcium wave propagation velocity (CPV). We hypothesize that hypoxic CMs alter the calcium handling in adjacent normoxic CMs across an O2 gradient landscape via cell‐cell contact and/or paracrine‐mediated mechanisms. Methods: We engineered a polydimethylsiloxane (PDMS) microphysiological system with buried, gas‐perfused microchannels to maintain a spatial O2 gradient. An overlying PDMS gas diffusion membrane was microcontact printed with a fibronectin line pattern to culture anisotropic monolayers of neonatal rat ventricular myocytes (NRVMs) on the device surface. The O2 gradient profile was validated using fluorescent O2 sensors. After 4 hours of O2 modulation, the fluorescent calcium indicator Fluo‐4 was used to measure calcium transients and CPV during 1 Hz electrical pacing. Results: Calcium transient analysis showed an increase in the time to peak in normoxic NRVMs within the O2 gradient as compared to adjacent hypoxic NRVMs in the gradient (p < 0.05) and homogenous hypoxic (p < 0.01) and homogenous normoxic (p < 0.001) control devices. The presence of the O2 gradient also increased the time constant of decay as compared to the controls (p < 0.01). CPV results showed that transverse velocity was slower in normoxic NRVMs within the O2 gradient compared to the homogenous normoxic control (5.3 ± 3.9 vs. 13.4 ± 3.2 cm/s, p=0.02). Conclusions: Overall, the data demonstrate that there is a delayed excitation and delayed recovery of calcium transients in CMs exposed to normoxia in an O2 gradient. Additionally, the transverse CPV in normoxic CMs in the gradient is driven by the nearby hypoxic CMs. Our in vitro border zone O2 landscape allows us to investigate ongoing interactions between normoxic and hypoxic CMs, which is key to developing a better understanding of the effects of acute MI, uncovering the mechanisms of post‐MI remodeling, and creating novel therapies to minimize myocardial damage and the expansion of hypoxic cardiac injury. [ABSTRACT FROM AUTHOR]