Yale University's biomedical engineers have hit upon a workable possbilility that may help stop HIV infection in the future - where nanoparticles can be used as a safe measure to deliver potentially therapeutic RNAs into vaginal cells.

Led by Mark Saltzman, the researchers believe that similar particles could be used to make topical creams containing anti-HIV RNAs.

The team wanted to find a better way to deliver short interfering RNAs (siRNAs) into vaginal cells that might come into contact with HIV.

These short snippets of RNA can be designed to repress specific genes, and siRNAs against HIV genes have been shown to stop the virus reproducing in humanized mice.

Usually, siRNAs are transferred into cells by attaching them to lipids, which is expensive and can be toxic, reports Nature.

In the new study, however, the scientists instead found a surprisingly simple way to pack thousands of siRNAs into nano-sized bits of a biodegradable and biocompatible plastic that is already approved for medical uses.

Such nanoparticles could then be incorporated into a vaginal gel, which could be applied by women before sex to help prevent infection.

"It's surprising that you can load as much siRNA as you can into particles like this. It wasn't obvious that it would work," said Saltzman.

For developing the new method, the team first mixed the siRNA molecules with spermidine - a natural condensing agent, which formed the siRNA into clumps that were later encapsulated in porous plastic particles 100 nanometres across.