Substrate elasticity and surface tension mediate the spontaneous rotation of active chiral droplet on soft substrates

Abstract

Active chirality is an universal property of macromolecules as well as cellular systems and processes, such as nucleic acid, proteins, bacterial flagella and its motions, actomyosin filaments and network, and the left–right (LR) asymmetric morphogenesis, etc. Despite of attempts to elucidate the relations among cellular chirality, spontaneous cellular rotation and extracellular matrix properties, many features of the chiral active matter that are in contact with elastic substrates are still not clear in terms of fundamental physical principles. For instance, when an active chiral droplet in contact with an elastic substrate, the underline interplay among surface elasticity, chirality, and surface tension is largely unknown. In this work, based on the Gurtin–Murdoch surface elasticity we developed an adhesive surface hydro-elasticity theory of moving line to model and simulate the spontaneous rotation of a chiral active soft matter droplet on soft elastic substrates to study the rich morphological, conformational, and dynamic behaviors of the droplet/substrate interaction. In this study, we have found that both surface tension and substrate elasticity significantly affect the spontaneous rotation of the active chiral droplet on the substrate from several crucial aspects: (1) the geometry and morphology of the rotating droplet; (2) the angular velocity and helical vertices of the rotating droplet; (3) the order parameter distribution inside the rotating droplet, (4) the dynamic contact area of the rotating droplet, and (5) the contact stress distribution in both the droplet as well as the elastic substrate.