Figure 1.

ECT formation and chronic optical pacing (C-OP) protocol: (a) ECTs were generated from a multi-component mixture of cardiomyocytes, endothelial cells, and mural cells, differentiated from h-iPSCs. Cells were mixed with culture medium, collagen I, and Matrigel. AAV1/2-CAG-oChIEF-tdTomato virus was then added to the gel mixture at 500 MOI. The gel mixture was poured into FlexCell® TissueTrain® wells deformed into a cylindrical mold by vacuum suction and anchored by nylon mesh tabs. The TissueTrain® plate was placed on top of an Arduino-controlled LED platform for chronic optical pacing. ECTs were cultured at 37 C, 5% CO₂. (b) At culture day 7, C-OP was initiated. C-OP ECTs were stimulated with a pulsed 470 nm LED. A representative C-OP protocol is shown. At each culture day, we measured the maximum capture rate (MCR) and set the C-OP rate at 0.5 Hz below MCR.