Analysis of elastic strains reveals shape selection pathways in active gels*

Myosin motor-induced forces in the actin cytoskeleton are responsible for cell and tissue shape changes in living systems. We consider in vitro experiments where a set of actomyosin gel disks spontaneously contract and buckle into a family of initial-geometry dependent, 3D shapes ranging from domes to wrinkled [1]. We perform particle imaging velocimetry (PIV) analysis on gels of different initial shapes to obtain the in-plane distribution of elastic strains. Resolving the radial and azimuthal components of strain reveals the robust occurrence of an inner isotropic contracting region, surrounded by an outer region with radial stretching. Comparison with a model for active stresses in elastic disks allows us to infer an outer region with aligned force dipoles representing myosin activity. Our findings support the hypothesis that this differential distribution of active stresses arises from the contraction-induced local alignment of actin bundles along the gel boundary. Future work will reveal how the in-plane strain distribution determines the final 3D buckled shapes.

1. “Artificial contractile actomyosin gels recreate the curved and wrinkling shapes of cells and tissues” by G. Livne et al., biorXiv 2023.03.21.533327