The effectiveness of microbicidal gels, topical products developed to prevent infection by sexually transmitted diseases
including HIV/AIDS, is governed by extent of gel coverage, pharmacokinetics of active pharmaceutical ingredients
(APIs), and integrity of vaginal epithelium. While biopsies provide localized information about drug delivery and tissue
structure, in vivo measurements are preferable in providing objective data on API and gel coating distribution as well as
tissue integrity. We are developing a system combining confocal fluorescence microscopy with optical coherence
tomography (OCT) to simultaneously measure local concentrations and diffusion coefficients of APIs during transport
from microbicidal gels into tissue, while assessing tissue integrity. The confocal module acquires 2-D images of
fluorescent APIs multiple times per second allowing analysis of lateral diffusion kinetics. The custom Fourier domain
OCT module has a maximum a-scan rate of 54 kHz and provides depth-resolved tissue integrity information coregistered
with the confocal fluorescence measurements. The combined system is validated by imaging phantoms with a
surrogate fluorophore. Time-resolved API concentration measured at fixed depths is analyzed for diffusion kinetics.
This multimodal system will eventually be implemented in vivo for objective evaluation of microbicide product
performance.
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