Publications

A major challenge in cardiac research is the limited translatability of drug screening and toxicity assays due to the use of in vitro models that poorly mimic the native cardiac environment. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) offer a promising route forward, but conventional 2D culture on rigid substrates hinders their functional maturation and predictive accuracy. This study addresses this problem by investigating the effect of hybrid fibronectin-based hydrogels with tunable stiffness on the mechanical and electrical properties of hiPSC-CMs. We engineered hydrogels with stiffness mimicking the lowest range of neonatal heart tissue stiffness (2-4 kPa) and compared hiPSC-CM behavior on these substrates to that on standard fibronectin-coated glass. Our results demonstrate that hydrogel culture promotes more uniform and stable cardiomyocyte contractions, as evidenced by increased single peak percentages and altered contraction duration. Electrophysiological analysis revealed that hydrogel stiffness influences action potential duration and signal amplitude. Furthermore, hiPSC-CMs on hydrogels exhibited enhanced cell-matrix and cell-cell adhesion, indicating improved structural and functional connectivity. Drug testing with known cardioactive compounds, including isoproterenol and nifedipine, revealed distinct differences in drug responses between hydrogel and glass cultures, suggesting that hydrogels provide a more physiologically relevant platform for assessing drug effects. This work highlights the potential of engineered hydrogel substrates to enhance the functional maturity and predictive accuracy of hiPSC-CMs for cardiac research and drug development.

JTD Keywords: Action potentials, Beat, Cell adhesion, Cell differentiation, Cells, Cells, cultured, Contraction, Fibronectins, Guinea-pig, Humans, Hydrogels, Induced pluripotent stem cells, Ipsc-cardiomyocytes, Ipsc‐cardiomyocytes, Isoproterenol, Maturation, Mechanical properties, Myocytes, cardiac, Nifedipine, Phenotype, Platform, Sensitive dye di-4-anepps

Traction force microscopy (TFM) quantifies cellular forces at the cell-extracellular matrix interface, yet elastic formulations neglect viscous dissipation and can misinterpret cellular forces on viscoelastic substrates. We introduce a semi-analytical 2D viscoelastic TFM (veTFM) that generalizes the Boussinesq framework of elastic TFM to Generalized Maxwell (GMX) substrates with one or two components. By combining Fourier and Laplace transforms, veTFM quantifies time-resolved tractions in finite-thickness substrates and resolves stress-free reference and substrate pre-stress. We derive criteria for when elastic regimes remain valid in this framework. This positions veTFM as a scalable extension of standard 2D TFM (eTFM) to viscoelastic substrates, identifying when eTFM remains sufficient, which elastic limit applies, and when full viscoelastic quantification is required. Applied to beating cardiomyocytes, epithelial cells, and dermal fibroblasts cultured on linear-polyacrylamide and alginate viscoelastic hydrogels, veTFM shows that the elastic or viscoelastic regime engaged by the cell depends on timescale matching between the loading rate and the substrate's relaxation times. Notably, for the Generalized Maxwell substrates analyzed here, viscoelastic traction magnitudes scale with the substrate's total dissipation rather than individual relaxation times, with total dissipation setting traction magnitude and timescale matching determining whether the cell engages the substrate in an elastic or viscoelastic regime.

JTD Keywords: Animals, Biomaterials, Cell, Cell-material interactions, Cell–material interactions, Elasticity, Epithelial cells, Extracellular matrix, Extracellular-matrix viscoelasticity, Fibroblasts, Focal adhesions, Guide, Humans, Hydrogels, Microscopy, atomic force, Myocytes, cardiac, Numerical inversion, Semi-analytical methods, Semi‐analytical methods, Stress relaxation, Viscoelastic hydrogels, Viscoelastic traction force microscopy, Viscosity