Semi-solid gels function as physical barriers to human immunodeficiency virus transport in vitro

Area of Science:

• Biomedical Sciences
• Virology
• Materials Science

Background:

• Vaginal gels are explored as physical barriers against HIV transmission during sexual contact.
• The efficacy of these gels as barriers depends on their ability to impede the transport of HIV virions.
• Understanding HIV transport dynamics within gel matrices is critical for evaluating microbicide products.

Purpose of the Study:

• To quantify the diffusion of HIV virions within semi-solid gel formulations.
• To assess the barrier function of thin gel layers against HIV transport.
• To provide baseline data for the design of novel HIV barrier products and interpretation of microbicide trials.

Main Methods:

• Quantification of HIV virion diffusion coefficients in hydroxyethyl cellulose (HEC) and methylcellulose (MC) gels.
• Utilized a Transwell system to evaluate the barrier efficacy of approximately 150-μm thick gel layers.
• Measured HIV transport reduction over 0, 4, and 8-hour incubation periods.

Main Results:

• HIV diffusion coefficients in undiluted HEC and MC gels were significantly reduced (4±2 x 10⁻¹² and 7±1 x 10⁻¹² cm²/s, respectively), approximately 10,000 times lower than in water.
• Substantial gel dilution was required to increase diffusion coefficients by two orders of magnitude.
• Gel layers demonstrated a log reduction in HIV transport across the Transwell membrane.

Conclusions:

• Hydroxyethyl cellulose (HEC) and methylcellulose (MC) gels act as effective in vitro physical barriers to HIV transport.
• The barrier function is influenced by gel concentration, distribution, and dilution by physiological fluids.
• The physical barrier properties of placebo gels must be considered in the design and interpretation of microbicide clinical trials.