Glutamax 1 100

MEFs were obtained from E13.5 as described in^{81 (link)}. MEFs were cultured at 37 °C under 5% CO₂ in Dulbecco’s Modified Eagle Medium (DMEM) (Thermo Fisher Scientific, 12800082), supplemented with 10% FBS (Capricorn Scientific, FBS-11A), 1x penicillin & streptomycin 10x (Capricorn Scientific, PS-B), 1x GlutaMax-I 100× (Thermo Fisher Scientific, 35050061). For subculture cells were rinsed with 1 × PBS and detached using 0.25% trypsin-EDTA at 37 °C for 3 min. Cells were typically split every 2–3 days at a 1:2 ratio. Flow cytometry showed more than 80% Pdgfra positive cells (Supplementary Fig. 3b).

hiPSC-CMs were dissociated using two methods. For the PET coating optimization phase, the hiPS-CMs were dissociated using Collagenase A and suspended into a suspension medium containing KnockOut DMEM with 10% fetal bovine serum (Biosera, Nuaille, France), 1% non-essential amino acids (NEAA), 1% GlutaMAX-I (100×) (all from Thermo Fisher Scientific, Cibco, Billings, Montana, USA), and 0.5% penicillin/streptomycin (Lonza, Basel, Switzerland) [32 (link)].
To improve the purity of the hiPSC-CM population in the following experiments with PET 5, the cardiomyocytes were dissociated and separated from other cell types using magnetic-activated cell sorting (MACS) on day 21–27 of the differentiation. The cells were dissociated using a Multi Tissue Dissection Kit 3 (Miltenyi Biotec, Bergisch Gladbach, Germany) following the manufacturer’s instructions. MACS sorting was performed using PSC-Derived Cardiomyocyte Isolation Kit, human (Miltenyi Biotec, Bergisch Gladbach, Germany). After cell sorting, the cells were resuspended in the suspension medium described above and the cells were plated on the gelatin-coated PET 5 textiles and gelatin-coated glass coverslips, which were used as controls.