Shaping the heart: Structural and functional maturation of iPSC-cardiomyocytes in 3D-micro-scaffolds

Cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) represent the best cell source for cardiac regenerative purposes but retain an immature phenotype after differentiation with significant limitations compared to adult cardiomyocytes. Apart from an incomplete cardiomyocyte-specific structure and microarchitecture, cells show at the level of Ca²⁺ signaling only slow Ca²⁺ release and reuptake properties. Here, we investigated the effect of restructuring single iPSC-CMs in specially designed 3D-micro-scaffolds on cell morphology and Ca²⁺ handling. Using direct laser writing, rectangular-shaped scaffolds were produced and single iPSC-CMs were seeded into these forms. Structural analyses revealed strong sarcolemmal remodeling processes and myofilament reorientation in 3D-shaped cells leading to enhanced clustered expression of L-type Ca²⁺ channels and ryanodine receptors and consequently, to faster Ca²⁺ transient kinetics. Spontaneous beating activity was enhanced and Ca²⁺ handling was more robust compared to non-patterned cells. Overall, our data demonstrate for the first time significant improvement of Ca²⁺ signaling properties in reshaped iPSC-CMs indicative of functional maturation by structural remodeling.