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. 2025 May 13;8:745. doi: 10.1038/s42003-025-08162-0

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© The Author(s) 2025

Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

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Fig. 8 — aTop: Schematic illustration of the 3D EHT platform used to evaluate contractile function of CM-AI laser-processed hiPSC-derived atrial CMs. Right: Representative 10× brightfield image of a 3D EHT. The embedded magnet for force sensing is outlined in blue. Created in https://BioRender.comb Representative contractile force traces recorded from the same 3D EHT over time, demonstrating maturation of contractile performance. c Quantitative analysis of 3D EHT contractile function across multiple time points (Day 7, 22, and 36). Contraction frequency increased over time (Day 7 = 1.97 ± 0.13; Day 22 = 2.63 ± 0.12; Day 36 = 2.27 ± 0.12 Hz, n = 10). Peak contractile force increased over time (Day 7 = 25.9 ± 2.5; Day 22 = 38.0 ± 4.9; Day 36 = 53.3 ± 5.0 µN, n = 10). Contraction velocity increased over time (Day 7 = 327.3 ± 33.0; Day 22 = 516.4 ± 60.9; Day 36 = 650.5 ± 63.5 µN/s, n = 10). Relaxation velocity increased over time (Day 7 = 102.1 ± 10.6; Day 22 = 164.9 ± 19.7; Day 36 = 201.8 ± 18.9 µN/s, n = 10). Time to 50% peak of contraction (TTP 50%) increased from day 22 to 36 (Day 7 = 0.039 ± 0.0009; Day 22 = 0.034 ± 0.001; Day 36 = 0.040 ± 0.0008 s, n = 10). Time to 50% relaxation increased between days 22 and 36 (Day 7 = 0.048 ± 0.002; Day 22 = 0.040 ± 0.001; Day 36 = 0.051 ± 0.003 s, n = 10). All data represent repeated measurements from the same 10 3D EHTs at each time point. One way ANOVA; Friedman test; multiple comparisons; ****P < 0.0001; ***P = 0.0001. d Ivabradine treatment (0.3 nM) significantly reduced spontaneous beat rate (**P = 0.009, unpaired t-test and Kolmogorov–Smirnov test), while other contractile parameters remained unaffected. e Representative 3D EHT force traces at baseline and after vehicle control (VEH, dashed lines) treatment. f Representative force traces showing ivabradine treatment slowed the spontaneous beat rate of 3D EHTs as quantified in (d).