We are developing and applying a set of optical devices that measure characteristics of formulation coating in the human vagina, including local thickness and dilution, and local pH.
Fluorimetric Device
- Fiberoptic (endoscope) encased in transparent, phallus-shaped insertion device
- Formulation labeled with sodium fluorescein
- Some experiments include application of vaginal fluid or semen simulant labeled with indocyanine green
- Linear correlation between fluorescence intensity and local thickness of coating layer
- 35 - 50 micron spatial resolution of thickness
- Systematically map coating over vaginal surface adjacent to tube (inside of cylinder) using local fluorimetric readings and video images
We present here examples of measurements of spatial distributions of formulation coating thickness over the vaginal epithelial surfaces.
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We are developing biophysically relevant summary measures of the coating thickness distributions. These focus on:
Extent
- What fraction of the vaginal surface/volume contains detectable formulation?
- How thick is the local coating?
Location
- Where is the formulation located along the vaginal axes?
Uniformity/variability/continuity
- How smooth is the distribution?
- Are there bare spots? If so, what are their characteristics?
LCI Device
A multiplexed LCI (low coherence interferometry) instrument is being developed by our collaborator, Adam Wax, for use as a label-free, high-resolution method for intravaginal measurement of microbicidal gel distribution. LCI exploits the low coherence of broadband light to achieve depth-resolved thickness measurements with micron resolution.
The following plots show a comparison of gel thickness measurement linearity for the LCI system and the fluorimetry system. The LCI system achieves excellent response without the need for a fluorescent label.
In the future, the LCI system will be integrated into the fluorimetric system to allow simultaneous data collection.
Advantages of the LCI system:
- it is label-free
- it allows time-independent measurements - the time interval following gel application can be greatly increased
- micron spatial resolution of thickness