Natasha Cowley

Viscosity mediated deformation of active droplets.

Cell migration is central to many important biological processes such as wound healing and immune response. It is also prominent in many pathological processes for example cancer metastasis. Migrating cells experience a wide variety of external environments in vivo. Here we investigate the effects of the external viscosity on migration speed and cell shape.
We model a cell migrating using adhesion-independent strategies as a viscous droplet with an active boundary, analogous to the acto-myosin cortex. Where the active particles on the boundary are governed by an advection-diffusion equation. This results in a coupled nonlinear system. In order to understand the full nonlinear behaviour of the active droplet, we numerically solve the model equations using the immersed boundary method to implement the deformable active boundary.
Where there is no viscosity difference the active droplet shape and speed are in line with predictions from linear stability analysis. The introduction of a viscosity difference between the active droplet and the external fluid allows for deformation of the droplet and a reduction in the activity threshold required for droplet motion.