Development of contact irreversible electroporation using a comb-shaped miniature electrode

Irreversible electroporation (IRE) has been studied as a less invasive method for tumor treatment. Since the mechanism of the treatment is based on the fatal perforation of the cell membrane caused by an external electric field, a tumor can be ablated non-thermally if an appropriate electric field is selected. However, an electric field more than a few kV/cm is required to accomplish ablation. In this study, we aim to examine the feasibility of a comb-shaped miniature electrode for reducing the required voltage for IRE. The reduction of the applied voltage while maintaining the potential difference was realized by narrowing the gap between the electrodes. A 150-μm-wide miniature electrode with a 100-μm gap between its teeth was fabricated using photolithography. In the experiment, the electrode was contacted onto a tissue phantom consisting of fibroblasts cultured in agarose gel three-dimensionally. After the application of electric pulses, cell ablation depth was examined using fluorescent staining. The miniature electrode successfully ablated the cells at the surface of the tissue phantom by the application of 90 electric pulses at 100 V. The maximum and average ablation depth were 72.7 μm and 61.0 ± 11 μm, respectively, which was approximately 40 % of that estimated by the numerical analysis. Our study showed that the contact-IRE using a miniature electrode in the order of sub-millimeter does ablate the superficial cells of targeted tissues upon the application of electric pulses of less than 100 V; however, further studies are required to maximize the ablation depth under the constraint of limited applied voltage.