Imaging the electric field associated with mouse and human skin wounds

We have developed a noninvasive instrument called the bioelectric field imager (BFI) for mapping the electric field between the epidermis and the stratum corneum near wounds in both mouse and human skin. Rather than touching the skin, the BFI vibrates a small metal probe with a displacement of 180 mum in air above the skin to detect the surface potential of the epidermis through capacitative coupling. Here we describe our first application of the BFI measuring the electric field between the stratum corneum and epidermis at the margin of skin wounds in mice. We measured an electric field of 177+/-14 (61) mV/mm immediately upon wounding and the field lines pointed away from the wound in all directions around it. Because the wound current flows immediately upon wounding, this is the first signal indicating skin damage. This electric field is generated at the outer surface of the epidermis by the outward flow of the current of injury. An equal and opposite current must flow within the multilayered epidermis to generate an intraepidermal field with the negative pole at the wound site. Because the current flowing within the multilayered epidermis is spread over a larger area, the current density and subsequent E field generated in that region is expected to be smaller than that measured by the BFI beneath the stratum corneum. The field beneath the stratum corneum typically remained in the 150-200 mV/mm range for 3 days and then began to decline over the next few days, falling to zero once wound healing was complete. The mean wound field strength decreased by 64+/-7% following the application of the sodium channel blocker, amiloride, to the skin near the wound and increased by 82+/-21% following the application of the Cl- channel activator, prostaglandin E2.