Abstract
Living things enact control of non-equilibrium, dynamical structures through
complex biochemical networks, accomplishing spatiotemporally-orchestrated
physiological tasks such as cell division, motility, and embryogenesis. While
the exact minimal mechanisms needed to replicate these behaviors using
synthetic active materials are unknown, controlling the complex, often chaotic,
dynamics of active materials is essential to their implementation as engineered
life-like materials. Here, we demonstrate the use of external feedback control
to regulate and control the spatially-averaged speed of a model active material
with time-varying actuation through applied light. We systematically vary the
controller parameters to analyze the steady-state flow speed and temporal
fluctuations, finding the experimental results in excellent agreement with
predictions from both a minimal coarse-grained model and full
nematohydrodynamic simulations. Our findings demonstrate that
proportional-integral control can effectively regulate the dynamics of active
nematics in light of challenges posed by the constituents, such as sample
aging, protein aggregation, and sample-to-sample variability. As in living
things, deviations of active materials from their steady-state behavior can
arise from internal processes and we quantify the important consequences of
this coupling on the controlled behavior of the active nematic. Finally, the
interaction between the controller and the intrinsic timescales of the active
material can induce oscillatory behaviors in a regime of parameter space that
qualitatively matches predictions from our model. This work underscores the
potential of feedback control in manipulating the complex dynamics of active
matter, paving the way for more sophisticated control strategies in the design
of responsive, life-like materials.