  We illustrate a concept for shape-changing microswimmers, which exploits the
hysteresis of a shape transition of an elastic object, by an elastic disk
undergoing cyclic localized swelling. Driving the control parameter of a
hysteretic shape transition in a completely time-reversible manner gives rise
to a non-time-reversible shape sequence and a net swimming motion if the
elastic object is immersed into a viscous fluid. We prove this concept with a
microswimmer which is a flat circular elastic disk that undergoes a transition
into a dome-like shape by localized swelling of an inner disk. The control
parameter of this shape transition is a scalar swelling factor of the disk
material. With a fixed outer frame with an additional attractive interaction in
the central region, the shape transition between flat and dome-like shape
becomes hysteretic and resembles a hysteretic opening and closing of a scallop.
Employing Stokesian dynamics simulations of a discretized version of the disk
we show that the swimmer is effectively moving into the direction of the
opening of the dome in a viscous fluid if the swelling parameter is changed in
a time-reversible manner. The swimming mechanism can be qualitatively
reproduced by a simple 9-bead model.
