Excitable medium with left–right symmetry breaking

A chemical excitable medium was constructed where the velocities of wave propagation to the left and to the right are different. It consists of a network of the “chemical diode” elements, with a gap 150mm between the “presynaptic” and “postsynaptic” parts. With this gap, a chemical diode conducts excitation in both directions, but with different delays. The network was created by a new method: it was printed by a computer printer on a polysufone membrane preloaded with the catalyst of the reaction. Propagation of plane waves, circular waves and spiral rotating waves was studied. It was found that in an asymmetric medium: (1) Excitation wave length (“wave thickness”) is different for waves propagating to the left and to the right. (2) Target patterns are not of circular form. (3) Spiral waves are not stationary in this medium, they drift with constant velocity. The component C∥ of the drift is determined by the asymmetry of the medium, the component C⊥ is controlled by both the asymmetry and the chirality of the spiral.