Fig. 1: Study design and structural characterisation of iPSC-CMs.

a Schematic overview of the study design. Differentiated iPSC-CMs were digested on day 15-16 (d15-16) and randomly divided into 4 experimental groups to investigate the effects of maturation medium (MM), nanopatterning (NP) and electrostimulation (ES). Extensive characterisation of the cells was performed on day 42 (d42). For some experiments, including calcium imaging, seahorse assays and multi-electrode array measurements, iPSC-CMs were replated into the corresponding assay plates on d42 and allowed to recover for another 7 days. Created in BioRender. Li, W. (2025) https://BioRender.com/p85e700. b Representative morphology of iPSC-CMs under different conditions at d42. Scale bar, 200 µm for all four groups. c Representative immunostaining for α-actinin, cardiac ryanodine receptor (RYR2) and Hoechst33342. d Representative immunostaining for connexin 43 (Cx43), phalloidin and Hoechst33342. Data (b-d) are based on 3 independent experiments using 3 different iPSC lines. e, f Quantification of sarcomere alignment based on z-disk orientation (e) and nuclei elongation (f). The method used to analyse the sarcomere alignment is shown in Supplementary Fig. 1a. Data were obtained from 2 independent experiments using 2 iPSC lines (n = 4 images/group/experiment). Data are presented as averages of each experiment. Orange, red, blue and green bars represent the four experimental groups: B27, MM, MM + NP, and MM + NP + ES, respectively. Symbols denote iPSC lines: circles for isWT7, and squares for iWTD2. Source data are provided as a Source Data file.