MHz compression of pulse packets facilitates remote focusing of electroporation

Abstract

Stimulation by pulsed electric fields (PEFs) normally follows PEF strength and weakens with distance from electrodes. Bipolar cancellation, caused by the electric field reversal, can offset this dependence. Remote focusing can be achieved by stimulation with nanosecond pulse packets that generate multiphasic, bipolar interference patterns near electrodes while preserving unipolar PEF at the remote target. We studied how the packet repetition rate, pulse width, and packet number influence remote focusing of electroporation and its suppression near electrodes. Cell monolayers were electroporated by packets of 300-, 600-, or 900-ns pulses from four needle electrodes arranged in a square with 15.3-mm diagonals. Electroporative dye uptake peaked at the center of the square and decreased laterally following Lorentzian distribution. Higher packet rates, longer pulses, and a smaller number of packets sharpened the central peak, reducing its full width at half maximum (FWHM) to 1.1 mm, which was 7.3 % of the diagonal and just 2.3 % of the electrode array area. At 0.2 MHz, electroporation near electrodes was 40-fold weaker than at the center, despite a 4-fold stronger electric field. This near-complete suppression of off-target effects, combined with sharper remote focusing, provides a critical advantage for precise targeting of PEF effects in biomedical applications.