Abstract
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. 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 × 105μm/s compared to topical (0.1 μm/s) and needle injection (53 μm/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.
Highlights
For many centuries, needles and syringes have been extensively used in several medical procedures
We investigated the potential for continuous wave (CW)-induced jet injection to achieve deeper dispersion depths than with topical application or solid needle injections
For the needle-free experiments, higher laser energy absorption led to faster heating of the aqueous solution, which resulted in faster bubble expansion and higher jet velocities
Summary
Needles and syringes have been extensively used in several medical procedures. For just as long, injections are feared by many patients.. Pills or topical skin products are easier to use and are painless. Oral and transdermal administration routes are favored by patients and physicians alike.. Applied drugs via creams or patches exhibit slow drug uptake due to the passive delivery across the skin induced by a concentration gradient, in which the diffusion properties are a function of the skin characteristics and the solution molecules.. The slow diffusion originates primarily from the properties of the outermost skin layer, the stratum corneum (SC), which protects the underlying tissue from infections and dehydration.. Diffusion is only limited to lipophilic and low molecular weight drugs (< 500 g/mol).. The SC poses a great permeation challenge for most of the drugs and delivery methods since the majority has a high molecular weight and poor solubility.. Applied drugs via creams or patches exhibit slow drug uptake due to the passive delivery across the skin induced by a concentration gradient, in which the diffusion properties are a function of the skin characteristics and the solution molecules. The slow diffusion originates primarily from the properties of the outermost skin layer, the stratum corneum (SC), which protects the underlying tissue from infections and dehydration. In practice, diffusion is only limited to lipophilic and low molecular weight drugs (< 500 g/mol). the SC poses a great permeation challenge for most of the drugs and delivery methods since the majority has a high molecular weight and poor solubility. One alternative to the topical application is the use of microneedles, which are effective for breaking through
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