WRINKLING AND BUCKLING INSTABILITIES OF CONTRACTILE SUSPENDED ACTOMYOSIN SHEETS

In many biological processes tissues and cells present active shape deformations resulting in wrinkling and buckling through contraction that result from internal forces generated by motor proteins. In many cases, the contracting material is also coupled to an elastic substrate, presenting a major difficulty for studying contraction induced folding. Here, we present the study of contraction and buckling of active, initially homogeneous, thin elastic actomyosin gels isolated from bounding surfaces. We find that the gels exhibit dimensionally dependent contraction that starts at the system boundaries, proceeds into the bulk, and eventually leads to spontaneous buckling of the sheet at the periphery resulting in different three-dimensional shapes at steady state. While thin sheets end up in wrinkled structures of mean negative Gaussian curvature whose configurations are of a single wavy mode that refines with decreasing thickness, thick sheets end up in domes with mean positive Gaussian curvature. Note that regardless of their distinct contraction dynamics and final shape, both thin and thick sheets show similar volume reduction, inferring on similar material properties of the contracted gel. Our system provides a well-controlled platform for studying contraction-induced folding of actively self-organizing gel sheets, in the absence of confinement