Evaluation of transdermal drug delivery using terahertz pulsed imaging

Abstract

Transdermal drug delivery (TDD) is widely used for painless dosing due to its minimally invasive nature compared to hypodermic needle injection and its avoidance of the gastrointestinal tract. However, the stratum corneum obstructs the permeation of drugs into skin. Microneedle and nanoneedle patches are ways to enhance this permeation. In this work, terahertz (THz) imaging is utilized to compare the efficacy of different TDD methods including topical application and via a needle patch. Our work shows the feasibility and potential of using THz imaging to quantify and evaluate different transdermal application methods.

THz Sensing of Human Skin: A Review of Skin Modeling Approaches

“…As previously introduced, in vivo THz studies have mainly focused on skin due to the shallow penetration depth. Investigations into utilizing THz imaging for diagnosis of cancer, scar measurements, monitoring drug diffusion and hydration sensing have been reported [ 24 , 25 , 26 , 27 , 28 ]. The origin of these applications is mostly based on the sensitivity to water.…”

“…Wang et al show that THz imaging could be used as a label-free modality to evaluate the efficiency of different transdermal drug delivery methods including needle patches. They also revealed that the changes in the THz signal are caused by the drug solution displacing water inside skin, this means it is possible to extract the amount of drug solution that has penetrated into the skin [ 26 ].…”

“…where R N−j+1 represents the reflection from medium N − j + 1 to the inner layers until medium N, which is again calculated by Equation (26) if N − j + 1 < N − 1. exp means exponent. When N − j + 1 = N − 1 (i.e., j = 2), R N−1 equals to r N−1 and is calculated using the two-layer Fresnel reflection coefficients, depending on the angle of incidence and the polarization.…”

“…n N−j+1 and d N−j+1 are the complex refractive index and thickness of medium N − j + 1 respectively, and λ is the wavelength of the light. Therefore, the reflection from medium 0 to the inner layers is calculated by Equation (26) with j = N and repetitively substituting Equation (26) to calculate the reflections from the inner layers. The multiple layer Fresnel equation is theoretically equivalent to the impedanc method used in Bennett's work [51].…”

“…21, x FOR PEER REVIEW 16 of 2 refractive index and thickness of medium N-j+1 respectively, and is the wavelength o the light. Therefore, the reflection from medium 0 to the inner layers is calculated b Equation(26) with j = N and repetitively substituting Equation(26) to calculate th reflections from the inner layers.…”