Boundary Effects On Active Actin Gels

Cellular processes, such as endocytose, migration or division, are organized by the cytoskeleton. One important sub-process involved is the acto-myosin contraction.The actin-myosin network makes use of a unique building principle: actin filaments are connected by crosslink proteins and myosin motors apply contractile forces between them, creating an active gel. Three major regimes emerge: static network, global contraction and local contraction. The properties of the gel are not only determined by the protein concentrations, but also depend on geometry and growth conditions.Here we investigate the influence of boundary conditions on the active gel, with a focus on globally contracting systems. Remarkably we find affine contractions only for symmetrical geometries, asymmetry of the starting conditions leada to disturbances within the gel that develop differently over time. A rectangular system enhances its side aspect ratio over time during contraction, caused by its localized force responses.