In vitro electroporation is widely used as a vector delivery method for cell cultures, and has been for years. The in vivo technique works in much the same way as in vitro methods, in that an electric pulse is used to temporarily disrupt the cell membranes of the target tissue, allowing DNA to pass through.
In vivo electroporation is performed using a syringe that is pre-loaded with vaccine. Using an auto-injection system, a very low micro-second electric pulse is applied through the syringe needle immediately after the syringe releases vaccine into the target tissues. Methods without needles have worked in rodents, but not in mammals, therefore the needle is needed for human subjects. Inovio first developed an intermuscular method, using one-inch needles, that cause some discomfort. However, according to an interview with CEO Dr. Joseph Kim, newer interdermal methods using a 3 mm needle are much less penetrating and cause less pain.