  Clockwise rotational movement of isolated single cilia in mice embryo was
investigated in vivo. The movement generates leftward fluid flow in the node
cavity and plays an important role in left-right determination. The leftward
unidirectional flow results from tilting of the rotational axis of the cilium
to posterior side. Because of the no-slip boundary condition at the cell
surface, the upper stroke away from the boundary generates leftward flow, and
the lower stroke close to the boundary generates slower rightward flow. By
combining computational fluid dynamics with experimental observations, we
demonstrate that the leftward stroke can be more effective than expected for
cases in which cilia tilting alone is considered with the no-slip condition
under constant driving force. Our results suggest that the driving force is
asymmetric and that it is determined by the tilting angle and open angle of the
rotating cilia. Specifically, it is maximized in the leftward stroke when the
cilia moves comparatively far from the boundary.
