Active polar fluid flow in finite droplets

Abstract

Abstract. We present a continuum level analytical model of a droplet of active contractile fluid consisting of filaments and motors. We calculate the steady state flows that result from a splayed polarisation of the filaments. We account for interaction with the external medium by imposing a viscous friction at the fixed droplet boundary. We then show that the droplet has non-zero force dipole and quadrupole moments, the latter of which is essential for self-propelled motion of the droplet at low Reynolds' number. Therefore, this calculation describes a simple mechanism for the motility of a droplet of active contractile fluid embedded in a three-dimensional environment, which is relevant to cell migration in confinement (for example, embedded within a gel or tissue). Our analytical results predict how the system depends on various parameters such as the effective friction coefficient, the phenomenological activity parameter and the splay of the imposed polarisation.

Generation of stationary and moving vortices in active polar fluids in the planar Taylor-Couette geometry

“…Similar to the results reported in Ref. [22], however, we have not found qualitatively new states for nonvanishing values of these parameters, neither for ν 1 positive nor negative. To further simplify the dynamic equations, we pose |p| 2 = 1.…”

“…It is based on conservation laws and broken continuous symmetries and captures the behavior close to thermodynamic equilibrium. This approach has been used to study the emergence of spontaneous flows [14,[16][17][18][19], notably in the context of cell locomotion [20][21][22]. Furthermore, hydrodynamic studies of the dynamic properties of point defects have been presented.…”

Spontaneous Division and Motility in Active Nematic Droplets

“…Like in the case of active polar droplets [36,37], motility is achieved by means of a spontaneous splay deformation arising from the instability of the configuration of lowest nematic energy (for which H ij = 0). As for static deformations, the droplet initially elongates as a consequence of the quadrupolar straining flow driven by the defects (Fig.…”

An introduction to the statistical physics of active matter: motility-induced phase separation and the “generic instability” of active gels

“…These are very general, and can have remarkable consequences. For instance this so-called "generic instability" can set into motion a droplet of active gel within an isotropic fluid [55][56][57]. This interesting phenomenon is depicted in Fig.…”