Fig. 3.

Analysis of sarcomere orientation upon optimized culture conditions. A The main direction of sarcomere filaments in iPSC CMs was similar as detected in neonatal cells. However, cultivation on structured surfaces (iPSC CM struCon) significantly improved the orientation of the sarcomere network, if compared to standard culture conditions (iPSC CM stanCon). B Contingency plot shows that optimized culture conditions increased the number of cells containing filaments with high direction quality (60°–90°), while the portion of cells with low directionality decreased. C–G Consistently, histograms and rose diagrams confirm the beneficial effects of prolonged culture period and structured surfaces on filament orientation, shown by peak formation between − 60° and 60°. H Quantitative assessment of filaments at given direction intervals confirm the increase of structures with higher orientation. I Representative images of treated groups with color-coded directionality of sarcomere structures (inserted color wheel). A high degree of orientation is found in adult CM (red color), while large amounts of green and blue color represent low sarcomere orientation, shown in neonatal CMs and iPSC CMs, cultured under standard conditions. Statistical analysis of sarcomere directionality was performed using Watson–Williams test, n = 41–58, *p < 0.05, **p < 0.01, ***p < 0.001, ^#p < 0.001 compared to all groups