Selective excitation of work-generating limit cycles in living chiral crystals

Nonreciprocity is a ubiquitous feature of nonequilibrium systems, and often gives rise to novel forms of order, phase transitions and excitations in active matter. In living chiral crystals (LCCs) formed by spinning starfish embryos, nonreciprocity results in the spontaneous excitation of sustained strain waves that correspond to limit cycle oscillations. Here, we show that these limit cycles can be excited in a controlled manner by applying external mechanical perturbations in the form of uniaxial step compression. By applying a step compression protocol over a wide range of compression rates, we show that excitation of limit cycles is highly selective, and is triggered only when the applied compression rate is comparable to the embryo rotation frequency. This resonant coupling between imposed and intrinsic timescales provides a mechanism for selective work extraction from LCC strain oscillations. By quantifying time reversal asymmetry as well as the odd mechanical properties of the LCC, we calculate the work generation capacity of limit cycles. Our results have potential implications for engineering living metamaterials.