Active Surfaces and Defect-Mediated Morphogenesis*

There is growing evidence for the importance of topological defects in morphogenesis with several recent experiments and simulations observing that the presence of defects fundamentally changes the morphodynamics of tissues and guides their shape changes. However, a detailed understanding and explanation of these observations is still missing.
We present an analytic theory describing the dynamics of an active surface, a two-dimensional deformable surface coupled to an active liquid crystal on the surface. We show how introducing defects can influence the dynamics of the active surface and, in particular, how a buckling-like instability can arise at the positon of a defect. We investigate the effect of the charge of the defect and supplement our analytic theory with simulations. Our findings offer an explanation for the recent observations and are relevant to understanding morphogenesis and active surfaces in general.