Transdermal drug delivery (TDD) has been recently highlighted as an alternative to oral delivery and hypodermic injections. Among many methods, drug delivery using a microneedle (MN) is one of the promising administration strategies due to its high skin permeability, mininal invasiveness, and ease of injection. In addition, microneedle-based TDD is explored for cosmetic and therapeutic purposes, rapidly developing market of microneedle industry for general population.
To date, visualization of microneedles inserted into biological tissue has primarily been performed ex vivo. MRI, CT and ultrasound imaging do not provide sufficient spatial resolution, and optical microscopy is not suitable because of their limited imaging depth; structure of microneedles located in 0.2~1mm into the skin cannot be visulalized.
Optical coherence tomography (OCT) is a non-invasive, cross-sectional optical imaging modality for biological tissue with high spatial resolution and acquisition speed. Compared with ultrasound imaging, it exhibits superior spatial resolution (1~10 um) and high sensitivity, while providing an imaging depth of biological tissue down to 1~2 mm. Here, we present in situ imaging and analysis of the penetration and dissolution characteristics of hyaluronic acid based MNs (HA-MN) with various needle heights in human skin in vivo. In contrast to other studies, we measured the actual penetration depths of the HA-MNs by considering the experimentally measured refractive index of HA in the solid state. For the dissolution dynamics of the HA-MNs, time-lapse structural alteration of the MNs could be clearly visualized, and the volumetric changes of the MNs were measured with an image analysis algorithm.
Seungri Song, Jung Dong Kim, Jung-hyun Bae, Sooho Chang, Soocheol Kim, Hyungsuk Lee, Dohyeon Jeong, Hong Kee Kim, and Chulmin Joo, "In vivo optical coherence tomography imaging of dissolution of hyaluronic acid microneedles in human skin (Conference Presentation)," Proc. SPIE 10046, Visualizing and Quantifying Drug Distribution in Tissue, 100460I (Presented at SPIE BiOS: January 29, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2251772.5370230222001.
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