Mucus membranes play an important role in the human body, providing a line of defense against conditions like acid reflux, inflammatory bowel disease and, in a way, pregnancy. When the mucus barrier inside the cervix relaxes during ovulation sperm is able to enter and fertilize the eggs, but scientists in Sweden have come up with a way to keep the door locked, raising the prospect of a hormone-free contraceptive that induces no side effects.

"The starting point for us has been to regard mucus membranes as a separate material that you can work with and modify," says Thomas Crouzier, a scientist at KTH Royal Institute of Technology in Stockholm and leader of the new research. "In order to do that, one must understand the mucus membrane's functions, including acting as a barrier that stops bacteria and viruses while allowing oxygen or nutrients to pass through."

The scientists homed in on two components of mucus gels called dextran polymers and cholera proteins, which diffuse throughout as the barrier breaks down. The team found they could manipulate this process with the addition of chitosan, a compound derived from crustacean shells that scientists have previously investigated for applications ranging from the promotion of wound-healing to increasing the shelf life of foods.

By cross-linking the mucus gel with chitosan, the team found they could apply the brakes to the diffusion of the dextran and cholera. In the lab using purified pig mucus, the researchers found this had the effect of tightening the barrier. If these kinds of results could be translated to humans, the team says the contraception could take the form of a small vaginal capsule that quickly dissolves, with the blocking effect taking place in just a few minutes.

"The polymeric material can close this possibility, and could prevent fertilization from occurring," Crouzier says. "In this way, we get a contraceptive that is not based on hormones and has no side effects."

The research was published in the journal Biomacromolecules.