Abstract: Ordered complex fluids, such as liquid crystals, have a long history of theory and experimental development in condensed matter and materials physics. Recently, however, many of the theoretical tools and concepts developed to study artificial materials have been shown to have relevance in a variety of different biological systems across many length and time-scales. When complemented by additional terms which accounting for the local transduction of chemical energy into mechanical work this gave birth to the field of ``Active Hydrodynamics’’.

In my talk, I will start by reviewing some key concepts from liquid crystal physics and active matter before discussing some specific examples which are relevant to biology.

Firstly I will discuss joint experiment and theory work on in vitro actomyosin. Observing in vitro reconstituted actomyosin with iSCAT microscopy, we report, for the first time, meta-stable swirling spiral- and vortex-like structures at intermediate concentrations of adenosine triphosphate (ATP). We then observe aster-like structures that form as ATP depletes prompts us to revisit active hydrodynamic descriptions of actomyosin remodelling, and in particular the notion of ATP-dependence.

We use a microscopic statistical model of myosin-II minifilaments to derive scaling relations that inform a perturbative approach to the (ATP-dependent) hydrodynamics of actomyosin. The implication of our analysis is that, at high ATP, myosin-II minifilaments are processive, whereas at low ATP, they are contractile. In other words, more power implies different work. Since actomyosin remodelling is the principal method by which eukaryotic cells change their shape and perform mechanical work, the notion that ATP is not only fuel but also potentially a regulator is a concept that has wide ranging biological significance.

Secondly, I will discuss some theoretical work I have done extending the notions of active hydrodynamics to deformable surfaces. I will present some simple examples of instabilities and morphology generation from the coupling between ordering, flows and shape and their relevance to morphogenetic processes, such as Hydra morphogenesis.