In vivo investigation of temporal effects and drug delivery induced by transdermal microneedles with optical coherence tomography

Transdermal drug-delivery systems (TDDS) have been a growing field in drug delivery because of their advantages over parenteral and oral administration. Recent studies illustrate that microneedles (MNs) can effectively penetrate through the stratum corneum barrier to facilitate drug delivery. However, the temporal effects on skin and drug diffusion are difficult to investigate in vivo. In this study, we used optical coherence tomography (OCT) to observe the process by which MNs dissolve and to investigate the temporal effects on mouse skin induced by MNs, including the morphological and vascular changes. Moreover, the recovery process of the skin was observed with OCT. Additionally, we proposed a method to observe drug delivery by estimation of cross-correlation relationship between sequential 2D OCT images obtained at the same location, reflecting the variation in the backscattered intensity due to the diffusion of the rhodamine molecules encapsulated in MNs. Our observations supported the hypothesis that the temporal effects on skin due to MNs, the dissolution of MNs, and the drug diffusion process can be quantitatively evaluated with OCT. The results showed that OCT can be a potential tool for in vivo monitoring of effects and outcomes when MNs are used as a TDDS.