Electronic Pneumatic Injection-Assisted Dermal Drug Delivery Visualized by Ex Vivo Confocal Microscopy

Abstract

Background and objectives: Electronic pneumatic injection (EPI) is a technique for dermal drug delivery, which is increasingly being used in clinical practice. However, only few studies have been reported on cutaneous drug distribution and related clinical endpoints. We aimed to visualize the immediate cutaneous drug distribution, changes in skin architecture, and related clinical endpoint of EPI.

Study design/materials and methods: Acridine orange (AO) solution was administered to ex vivo porcine skin by EPI at pressure levels from 4 to 6 bar with a fixed injection volume of 50 µl and nozzle size of 200 µm. Immediate cutaneous distribution was visualized using ex vivo confocal microscopy (EVCM). Changes in skin architecture were visualized using both EVCM and hematoxylin and eosin-stained cryosections.

Results: The defined immediate endpoint was a clinically visible papule formation on the skin. The pressure threshold to consistently induce a papule was 4 bar, achieving delivery of AO to the deep dermis (2319 µm axial and 5944 µm lateral distribution). Increasing the pressure level to 6 bar did not lead to significant differences in axial and lateral dispersion (P = 0.842, P = 0.905; respectively). A distinctively hemispherical distribution pattern was identified. Disruption of skin architecture occurred independently of pressure level, and consisted of subepidermal clefts, dermal vacuoles, and fragmented collagen.

Conclusions: This is the first study to relate a reproducible clinical endpoint to EPI-assisted immediate drug delivery using EVCM. An EPI-induced skin papule indicates dermal drug delivery throughout all layers of the dermis, independent of pressure level settings. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.

Keywords: biodistribution; dermatology; device; drug delivery; electronically-controlled; ex vivo confocal microscopy; needle-free injection; pneumatic device; skin.

Figure 1.

Skin papule as clinical endpoint. A skin papule served as predefined, clinical endpoint after electronic pneumatic injection (50 µl/injection) at 4 bar (A) and 6 bar (B). The pressure level did not have a significant effect on papule dimensions (P = 0.288), with a diameter of 6.0 mm (6.0–7.0) at 4 bar and 7.0 mm at 6 bar (6.0–7.5 mm). The nozzle of the electronic pneumatic injection device is shown (C).

Figure 2.

Electronic pneumatic injection induces deep dermal drug delivery. Fluorescence and composite images were captured using an ex vivo confocal microscope. Images show comparable fluorescent drug distribution of acridine orange in deep dermis following electronic pneumatic injection at 4 and 6 bar pressure level (acridine orange solution is green on fluorescence images and purple on composite images). The most commonly observed distribution pattern was hemispherical (A, B, and C). Mild variations in shape have been observed for both pressure levels (D, E, and F). (A–F) display separate representative biopsies.

Figure 3.

Disrupted skin architecture by electronic pneumatic injection. Composite image showing skin architecture (pink) disrupted by electronic pneumatic injection with acridine orange (purple) at 6 bar pressure level (left) and an untreated biopsy (right) using ex vivo confocal microscopy. Tissue disruption was similar for 4 and 6 bar pressure level. *, epidermal trauma at entry point of injection; ■, clefting between stratum basale and dermis; ▲, vacuoles in the dermis.

Figure 4.

Skin architecture disruption visualized on histology images. On frozen tissue sections, skin architecture disruption induced by electronic pneumatic injection was observed as vacuoles, fragmented collagen, and tissue gaps in the dermis. Three sections are shown of one representative biopsy for both 4 and 6 bar. The tissue disruptions are more prominent in close proximity to the point of entry. Untreated control with intact skin architecture is shown for comparison.