Figure 2.

(a) Depiction of the ElectroPen device including its parts, (b) comparison against a commercial electroporator, (c) source of the piezoelectric crystal in a lighter, (d) an image of the ePatch vaccine delivery platform,¹⁸ (e) image of ePatch compared to traditional syringe needles for scale, and (f/g) images of the microneedle electrode array. (h) While both approaches rely on electric pulses, the difference lies in the use of piezoelectricity enabling frugal hardware, compared to traditional capacitance discharge. [Panels (a–c) were reproduced (or adapted) with permission from ref 15. Copyright 2020, PLOS Biology. Panels (d–g) were reproduced (or adapted) with permission from ref 18. Copyright 2021, PNAS.]