Needle‐Free Injection Assisted Drug Delivery—Histological Characterization of Cutaneous Deposition

Background and Objectives Many cutaneous drug‐delivery techniques rely on passive diffusion to deliver topical compounds to the skin. When attempting to deliver drugs to thicker lesions, such as skin tumors, modalities that do not rely on diffusion may serve as a better drug‐delivery method. In this histological study, we aim to investigate the cutaneous delivery patterns of an electronic pneumatic needle‐free injection device. Study Design/Materials and Methods Needle‐free‐injection was investigated in 24 ex vivo porcine skin samples and one basal cell carcinoma (BCC) tissue sample. A needle‐free injection device with a nozzle size of 200 μm delivered 80 μl compound ink (0.1 cc black ink: 5.0 cc saline) at low (30%/3.1 bar; n = 6 porcine skin; n = 1 BCC tissue), medium (50%/3.9 bar; n = 6 porcine skin), high (65%/4.6 bar; n = 6 porcine skin), and stacked (30 + 50%/3.1 + 3.9 bar; n = 6 porcine skin) pressures. Depth, width, and depth of maximum width of ink deposition were evaluated on histological slides. Results Depositions with small ink‐lined vacuoles were seen intra‐dermally in all samples, including the BCC tissue. Deposition depth was similar at low and medium pressures (924 vs. 994 μm; P = 0.873) but increased significantly with high pressure (1,564 μm; P = 0.010). When injections were stacked (3.1 + 3.9 bar), the depth remained similar to that of a single injection (931 μm; P = 1.000). The width of the deposition stayed comparable for low, medium, and high pressures when a single needle‐free injection was performed (30% = 2,394 μm; 50% = 2,226 μm; and 65% = 2,757 μm; P = 0.09), but increased significantly with stacking (2,979 μm; P = 0.037). The depth of maximal width was superficially located in the papillary dermis at low and medium pressures (321 and 305 μm; P = 0.748) but shifted to the deeper reticular dermis with high pressure (950 μm; P = 0.004) and with stacking (734 μm; P = 0.004). Conclusions In conclusion, with an electronically controlled, pneumatic needle‐free injector, depth and width of a cutaneous deposition can be influenced by pressure and stacking, respectively. The pneumatic needle‐free injection can potentially serve as a viable drug‐delivery technique for cutaneous pathologies where dermal deposition is essential. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.