Effect of Electric Field on Partially Pinned Scroll Waves in Excitable Chemical Media

We present an investigation of the dynamics of a scroll wave partially pinned to an inert cylindrical obstacle under electrical forcing in a three-dimensional Belousov–Zhabotinsky excitable medium. The freely rotating part of the scroll wave is forced to drift toward the positive electrode, while the pinned part remains attached to the obstacle, causing the scroll wave filament to elongate and its shape to change over time. Breakups of the elongated filament are also observed before the scroll wave gradually unpins and moves away from the obstacle. We also performed simulations using the Oregonator model to corroborate the experimental findings. In addition, the simulations reveal the detailed dynamics of the scroll wave filament. As the filament elongates and its shape evolves, the filament end attached to the top wall of the system drifts linearly at an angle to the electric field. Both the drift velocity and the tilted angle increase with field strength. When approaching the front wall, the filament end may either bounce back or proceed toward it, depending on the field strength. Filament breakups occur when a curved segment contacts a wall. Finally, both experiments and simulations show that the time required for unpinning of such partially pinned scroll wave increases as the electric field strength decreases. This behavior contrasts with spiral wave unpinning in a thin layered medium, where unpinning occurs rapidly under a sufficiently strong electric field but fails if the applied field is weaker than a critical value, Eunpin. Although measuring Eunpin in our experiments is limited by interactions between the scroll wave and wave trains generated by the electrodes, simulations confirm the existence of Eunpin for the partially pinned scroll wave. The presented findings have significant implications for the manipulation of wave patterns in biological and chemical systems where scroll wave dynamics are critical, such as in the onset and progression of cardiac arrhythmias.