Drug diffusion within the skin with a needle-free micro-jet injection (NFI) device was compared with two wellestablished delivery methods: topical application and solid needle injection. A permanent make-up (PMU) machine, normally used for dermal pigmentation, was utilized as a solid needle injection method. For NFIs a continuous wave (CW) laser diode was used to create a bubble inside a microfluidic device containing a light absorbing solution. Each method delivered two different solutions into ex vivo porcine skin. The first solution consisted of a red dye (direct red 81) and rhodamine B in water. The second solution was direct red 81 and rhodamine B in water and glycerol. We measured the diffusion depth, width and surface area of the solutions in all the injected skin samples. The NFI has a higher vertical dispersion velocity of 3 9 10 5 lm/s compared to topical (0.1 lm/s) and needle injection (53 lm/s). The limitations and advantages of each method are discussed, and we conclude that the micro-jet injector represents a fast and minimally invasive injection method, while the solid needle injector causes notable tissue damage. In contrast, the topical method had the slowest diffusion rate but causes no visible damage to the skin.

Adjuvants play a critical role in the design and development of novel vaccines. Despite extensive research, only a handful of vaccine adjuvants have been approved for human use. Currently used adjuvants are mostly composed of components that are non‐native to the human body, such as aluminum salt, bacterial lipids, or foreign genomic material. Here, a new ionic‐liquid‐based adjuvant is explored, synthesized using two metabolites of the body, choline and lactic acid (ChoLa). ChoLa distributes the antigen efficiently upon injection, maintains antigen integrity, enhances immune infiltration at the injection site, and leads to a potent immune response against the antigen. Thus, it can serve as a promising safe adjuvant platform that can help to protect against pandemics and future infectious threats.

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Drug diffusion within the skin with a needle-free micro-jet injection (NFI) device was compared with two well-established delivery methods: topical application and solid needle injection. A permanent make-up (PMU) machine, normally used for dermal pigmentation, was utilized as a solid needle injection method. For NFIs a continuous wave (CW) laser diode was used to create a bubble inside a microfluidic device containing a light absorbing solution. Each method delivered two different solutions into ex-vivo porcine skin. The first solution consisted of a red dye (direct red 81) and rhodamine B in water. The second solution was direct red 81 and rhodamine B in water and glycerol. For PMU experiments, the skin samples were kept stationary and the diffusion depth, width and surface area were measured. The NFI has a higher vertical dispersion velocity of 3 × 10 5 /s compared to topical (0.1 µm/s) and needle injection (53 /s). The limitations and advantages of each method are discussed, and we conclude that the micro-jet injector represents a fast and minimally invasive injection method, while the solid needle injector causes notably tissue damage. In contrast, the topical method had the slowest diffusion rate but causes no visible damage to the skin.