Abstract below
Rushikesh Shinde, MSC
PhD student under the supervision of Andrew Callan-Jones
Active fluids on curved surfaces : Flow localisation, bistability and front propagation.
Abstract :
From the point of view of physics, living tissues display properties of active nematic (or more generally, ordered) fluids. The individual constituents of these systems convert chemical energy into mechanical work enabling them to flow on long time scales. These self-driven flows play a crucial role in biological processes like morphogenesis and tissue organisation.
Active gel theory is a hydrodynamic description of the long-timescale behavior of such systems, capturing their ability to generate spontaneous flows through actively generated stresses associated with the cell nematic field. However, these active flows, unless controled, are typically chaotic and disorganised, and it is not clear how these flows are tamed during biological morphogenesis, which requires robust, predictable behavior.
In this talk, I will give an overview of work from my PhD using active gel theory for curved surfaces that illustrates how tissue geometry (i.e., curvature) can aid in constraining active nematic flows. First, I will present recently published work[1] showing that for an active film on a curved, rigid substrate, a generic nematic (Frank) elastic energy coupling to extrinsic curvature can result in localized active flows to regions where the difference in principal curvatures is smallest. This leads to interesting differences with respect to flat space active instabilities, including threshold-less active flows, hysteresis and bistability, which I will describe in some detail.
Second, I will present unpublished work in which I show that the same coupling to curvature can trigger front propagation in the nematic alignment field. These front solutions exhibit distinct regimes: classic FKPP-like (‘pulled’) fronts, where a stable nematic order invades an unstable order, and ‘pushed’ fronts, where a stable order invades a metastable order. Such dynamics may serve as a potential mechanism for transmitting orientational cues in cellular or tissue contexts.
