Researchers from the University of Utah and Northwestern University have been studying an innovative new gel that may serve as a molecular female condom capable of blocking HIV and other pathogens from passing through. The gel solidifies when the vaginal environment’s pH level changes to more basic, as when semen is introduced, thus creating a physical mesh barrier with pores down to 30 nanometers in size, smaller than most viruses can pass through. The researchers hope that the new material may one day provide women with a discreet way to protect themselves from pregnancy and venereal diseases.
In 2006, Kiser and colleagues published a study on their development of another "molecular condom" to be applied vaginally as a liquid, turn into a gel coating at body temperature, then, in the presence of semen, turn liquid and release an anti-HIV drug.
Unfortunately, few antiviral drugs bind to and attack HIV in semen. And in Africa, high air temperatures prevent the gel from turning liquid so it could coat the vagina evenly, Kiser says.
The new "molecular condom" gel in the current study works in the opposite way. Like the old version, it changes in response to changes in pH – acidity or alkalinity – in the vagina caused by the introduction of semen during sex. But unlike the old gel, which became liquid at the higher (less acidic) pH of semen, the new "molecular condom" becomes a semisolid at the pH of semen, forming a mesh of "crosslinked" molecules.
The new gel is applied as a gel, and then becomes more solid and impenetrable as changes in pH alter the strength of the bond between the gel’s two key components, both of which are polymers, or long, chain-like molecules made of many smaller, repeating units: PBA, or phenylboronic acid, and SHA, or salicylhydroxamic acid.
The chemical bonds between the two polymers constantly attach and detach at normal, acidic vaginal pHs of about 4.8, allowing the gel to flow, Kiser says. But at a pH of 7.6 – the slightly alkaline condition when semen enters the vagina – the PBA and SHA polymers "crosslink" and stick tightly together, he adds.
Part of the new study characterized the flow of the gel.
"It flows at a vaginal pH, and the flow becomes slower and slower as pH increases, and it begins to act more solid at the pH of semen," Jay says. HIV moves slowly within the gel, even when the gel is at lower pHs (higher acidity) and still flowing, but the virus is blocked at higher pHs caused by the entry of semen into the vagina.
The crosslinked polymers form a mesh that is smaller than microscopic, and instead is nanoscopic – on the scale of atoms and molecules – with a mesh size of a mere 30 to 50 nanometers – or 30 to 50 billionths of a meter.
The gel also could help prevent AIDS by blocking movement of immune system cells that try to combat infectious agents but instead get hijacked by the AIDS virus.
Press release: An HIV-Blocking Gel for Women …
Abstract in Advanced Functional Materials: Modulation of Viscoelasticity and HIV Transport as a Function of pH in a Reversibly Crosslinked Hydrogel
(hat tip: NewScientist)