Tolerability of a piezoelectric microneedle electroporator in human subjects

Abstract

Electroporation, or the use of electric pulses to facilitate the intracellular delivery of DNA, RNA, and other molecules, is a well-established technique, that has been demonstrated to significantly augment the immunogenicity of DNA/mRNA vaccines and therapeutics. However, the clinical translation of traditional electroporators has been limited due to high costs, large size, complex user operation, and poor tolerability in humans due to nerve stimulation. In prior work, we introduced ePatch: an ultra-low-cost, handheld, battery-free electroporator employing a piezoelectric pulser coupled with a microneedle electrode array that showed enhanced immunogenic responses to an intradermal SARS-CoV-2 DNA vaccine in mice. The current study shifts focus from efficacy to tolerability, hypothesizing that ePatch's microneedle array, which localizes the electric field to the superficial skin strata, will minimize nerve stimulation and improve patient comfort. We tested this hypothesis in 14 healthy adults, monitoring pain and other potential adverse effects associated with electroporation. Compared to the insertion of a traditional hypodermic needle, the ePatch was less painful. Adverse effects such as pain, tenderness, erythema and swelling at the application sites were minimal, transient, and statistically indistinguishable between the experimental and placebo ePatch application, suggesting excellent tolerability towards electroporation. In summary, ePatch has a favorable tolerability profile in humans and offers the potential for the safe use of electroporation in a variety of clinical settings, including DNA and mRNA vaccination.

Keywords: DNA/RNA vaccination; electroporation; human skin tolerability; microneedle electrode array.

FIGURE 1

ePatch administration to human subjects. (a) Schematic showing the experimental setup used to perform ePatch application to human subjects. (b) Assembled ePatch held in investigator's hand for a size comparison. (c) Representative photographic images of: the MEA of an ePatch applied on the skin of a study participant, an MEA with exposed microneedles, and a single row of 9 stainless steel microneedles.

FIGURE 2

Visual analog scale (VAS) pain scores of ePatch compared with hypodermic needle control in human subjects. VAS scores reported by study participants for five different study groups: (a) absolute VAS scores (n = 14), (b) VAS scores normalized to VAS scores experienced during insertion of a 25G hypodermic needle control (nVAS_HN) (n = 14) and (c) VAS scores normalized by VAS scores experienced by application of an ePatch without pulses (nVAS_NP) (n = 11 since the VAS for ePatch with no pulses was zero for three participants). The score of each subject was normalized to their own baseline score. In addition to box and whisker plots, and semi‐violin plots, individual data points (represented by filled circles) are also presented. The box indicates the range between the 25th and 75th percentiles, while the line inside the box represents the median. The whiskers show the maximum and minimum values of the dataset. The outliers are denoted by empty circles, which indicate values that exceed 1.5 times the interquartile range (the range between the 25th and 75th percentiles). In addition to box plots, semi‐violin plots represent the density of the data where the width indicates the frequency of the data points. Statistical significance was determined by the Wilcoxon rank sum test: *p < 0.05, **p < 0.01, and ***p < 0.001.

FIGURE 3

Skin tolerability immediately after application of ePatch and hypodermic needle control in human subjects. Ten minutes after skin treatment, (a) pain and (b) tenderness were assessed subjectively by study participants and (c) erythema size, (d) erythema intensity, and (e) induration/swelling were assessed visually by the clinical investigator and evaluated using a 0–4 point scale score sheet (see Table S1, Supplementary Information) (n = 14).

FIGURE 4

Skin tolerability 1 day after application of ePatch and hypodermic needle control in human subjects. One day after skin treatment, (a) pain, and (b) tenderness were assessed subjectively by study participants and (c) erythema size, (d) erythema intensity, and (e) induration/swelling were assessed visually by a study investigator and evaluated using a 0–4 point scale score sheet (see Table S1, Supplementary Information) (n = 9).

FIGURE 5

Skin appearance after application of ePatch and hypodermic needle control in human subjects. Photographic images of the forearm skin of a representative study participant are presented at 0 min, 10 min, 30 min or 1 day after skin treatment with ePatch or hypodermic needle insertion. The dashed line identifies sites of ePatch or hypodermic needle treatment. Black ink dots were applied to the skin to identify treatment sites.

FIGURE 6

Skin tolerability after application of ePatch in rats. (a) Representative photographic images of skin appearance over time for untreated skin and for skin after treatment by ePatch with 10 pulses. (b) Representative histological cross sections (H&E stained) of untreated skin and of skin 1 day after treatment by ePatch with 10 pulses.