  Emergence of collective dynamical chirality (CDC) at mesoscopic scales plays
a key role in many formation processes of chiral structures in nature, which
may also provide possible routines for people to fabricate complex chiral
architectures. So far, most of reported CDCs are found in systems of active
objects with individual structure chirality or/and dynamical chirality, and
whether CDC can arise from simple and achiral units is still an attractive
mystery. Here, we report a spontaneous formation of CDC in a system of both
dynamically and structurally achiral particles motivated by active motion of
cells. Active moving, confinement and hydrodynamic interaction are found to be
the three key factors. Detailed analysis shows that the system can support
abundant collective dynamical behaviors, including rotating droplet, rotating
bubble, CDC oscillation, array of collective rotation, as well as interesting
transitions such as chirality transition, structure transition and state
reentrance.
