Painless electroporation with a new needle-free microelectrode array to enhance transdermal drug delivery

A microelectrode array was designed to minimize the pain sensation of electroporation for enhancing transdermal drug delivery. The influence of the size of the electrode–skin contact area and of the distance between electrodes on the pain sensation was tested on human volunteers. The pain level decreased with the dimension of electrode–skin contact area and with inter-electrode distance. When both reached about 0.5 mm, the pain level was not perceptible even at the threshold of transdermal electroporation level of sixty electric pulses at 150 V, 1 ms at 1–10 Hz. An array of 11 × 11 alternately connected electrodes with 0.6 × 0.6 mm dimension was fabricated. The electric thresholds for effective drug delivery, using toluidine blue O as a marker on mouse skin, was found to be the same for microelectrode arrays as for larger electrodes and wider inter-electrode distances. In vivo transdermal electroporation using microelectrode array with 180 pulses of 150 V, 0.2 ms at 1 Hz, followed by 30 min methotrexate (MTX) occlusion increased more than 4 fold the systemic MTX level in mice. The results demonstrated the potential of painless delivery of significant amounts of chemotherapeutic agents through skin with the new electrode arrays in a clinical setting.