Vasalgel's success in rabbits suggests an effective, less permanent alternative to vasectomy for male contraception could be around the corner. Photo by Studio KIWI/Shutterstock

WASHINGTON, March 30 (UPI) -- Researchers found an injectible gel was an effective contraceptive, preventing the presence of sperm in rabbits' semen in a study.

The gel, called Vasalgel, completely stopped the flow of sperm after being injected into rabbits, and the natural flow of sperm returned when the gel was removed, researchers report in a new study.


Vasalgel would be the first contraceptive option for men that is not permanent, the researches say, as vasectomy is effective, but also generally considered permanent.

The gel, consisting of a styrene-alt-maleic acid dissolved in dimethyl sulfoxide, is injected into the vas deferens, where it becomes a hydrogel that allows water-soluble molecules to pass through but not sperm. Because it is soft, it can flex and stay in place, keeping sperm from squeezing through.

"Results from our study in rabbits were even better than expected," Dr. Donald Waller, a professor of pharmacology and toxicology at the University of Illinois, said in a press release. "Vasalgel produces a very rapid contraceptive effect which lasted throughout the study due to its unique hydrogel properties. These features are important considerations for a contraceptive product to be used in humans."

For the study, published in the journal Basic and Clinical Andrology, 12 rabbits were treated with two formulations of Vasalgel, one being a 100 percent SMA acid and the other an 80 percent SMA acid blended with 20 percent SMA anhydride.

In 11 of the 12 rabbits, sperm was not detected in semen at all once they'd received an injection. One of the rabbits showed the presence of a small number of sperm in early samples but eventually became azoospermic as well.

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Researchers are currently planning a human clinical trial for late 2016.