Experimental strategies for investigating passive and ultrasound-enhanced transdermal drug delivery

[摘要] (cont.) and confocal microscopy, respectively) were utilized to compare the delivery of 10-nm and 20- nm cationic, neutral, and anionic quantum dots into US/SLS-treated and untreated pig STS. The findings include: (a) ~0.01% of the quantum dots penetrated the dermis of untreated skin (which was quantified for the first time), (b) the quantum dots fully permeated US/SLS-treated skin, (c) the two cationic quantum dots studied exhibited different extents of skin penetration and dermal clearance, and (d) the quantum dot skin penetration is heterogeneous (which was determined using a novel application of confocal microscopy). Routes of nanoparticle skin penetration are discussed, as well as the application of the methods described herein to address conflicting literature reports on nanoparticle skin penetration in the context of nanoparticle skin toxicity. US/SLS treatment is concluded to significantly enhance quantum dot transdermal penetration by 500 - 1300%. The findings suggest that an optimum surface charge exists for nanoparticle skin penetration, and motivate the application of nanoparticle carriers to US/SLS-treated skin for enhanced transdermal drug delivery. The final investigation of this thesis focused on chemical penetration enhancers, which are used to enhance drug delivery through several biological membranes, particularly the stratum corneum of the skin. However, the fundamental mechanisms that govern the interactions between penetration enhancers and membranes are not fully understood. Therefore, the goal of this work was to identify naturally fluorescent penetration enhancers (FPEs) in order to utilize well-established fluorescence techniques to directly study the behavior of FPEs within the skin. In this study, 12 FPE candidates were selected and ranked according to their potency as skin penetration enhancers. The best FPEs found compared well to SLS, a well-known potent skin penetration enhancer. Based on the ranking of the FPEs, FPE design principles are presented. In addition, to illustrate the novel, direct, and non-invasive visualization of the behavior of FPEs within skin, three case studies involving the use of two-photon fluorescence microscopy are presented, including visualizing glycerol-mitigated and US-enhanced FPE skin penetration. Previous two-photon fluorescence microscopy studies have indirectly visualized the effect of penetration enhancers on skin by using a fluorescent permeant to probe the transdermal pathways of the penetration enhancer. These effects can now be directly visualized and investigated using FPEs. The combination of FPEs with fluorescence techniques represents a useful new approach for elucidating the mechanisms involved in penetration enhancement and membrane irritation, and for improving structure-activity relationships for penetration enhancers. The new physical insights obtained using FPEs will aid in designing effective penetration enhancers for drug delivery applications, including penetration enhancers to be combined with US for synergistically enhancing transdermal drug delivery. The experimental strategies presented in this thesis pave the way for investigations in several transdermal fields, including evaluating nanoparticle skin toxicity, designing nanoparticle drug delivery carriers, evaluating ultrasound-assisted transdermal vaccination, elucidating mechanisms of chemical penetration enhancer-induced skin irritation, designing topical formulations with penetration enhancers, and elucidating mechanisms of ultrasound and penetration enhancer synergism in enhancing skin permeability.

[发布机构] Massachusetts Institute of Technology