The spontaneous emergence of collective flows is a generic property of active fluids and often leads to chaotic flow patterns characterised by swirls, jets, and topological disclinations in their orientation field. However, the ability to achieve structured flows and ordered disclinations is of particular importance in the design and control of active systems. By confining an active nematic fluid within a channel, we find a regular motion of disclinations, in conjunction with a well defined and dynamic vortex lattice. As pairs of moving disclinations travel through the channel, they continually exchange partners producing a dynamic ordered state, reminiscent of Ceilidh dancing. We anticipate that this biomimetic ability to self-assemble organised topological disclinations and dynamically structured flow fields in engineered geometries will pave the road towards establishing new active topological microfluidic devices.

Researchers demonstrate that encapsulation is not necessary to achieve controlled, long-term protein release.

An ordered array of symmetric rotors immersed in active turbulence can turn persistently.

Significance: Methods to manipulate and control the dynamics of spontaneously flowing active materials are vital if these fluids are to lead to technological applications. We report the development of an easy-to-implement technique to achieve tunable, local control over active nematic films, the preeminent example of active fluids. We establish that micropatterns, fully submersed below active films, have a pronounced impact on dynamics. To showcase the adaptability of our technique, we present four proof-of-concept microstructures: trenches, undulated sinusoids, stairways, and pillars. Each illustrates a particular strength of our approach, including enacting abrupt virtual boundaries to trap topological defects, separating distinct flow states at constant levels of biochemical fuel, gently guiding self-propelled defects, and modifying local active nematic composition.