The research is in its early days, but Chinese scientists say they're using bartenders' tricks to stir up a new, reversible male contraceptive.
In experiments with rats, the method successfully kept sexually active males from impregnating females for more than two months.
"The two most widely used male contraceptives are condom and vasectomy," noted a team led by Xiaolei Wang, of Nanchang University. "A reliable and reversible medium-term [2 to 20 weeks] contraceptive method between the one-off condom and permanent contraception is urgently needed."
Their potential solution was inspired by the colourful layered cocktails often concocted by bartenders. In these mixes, liquids form distinct layers in a glass. But when stirred or heated, the layers combine into a uniform liquid.
Promising, but a long way to go
So, Wang's group developed a form of male contraception in which layers of materials are injected into the vas deferens - the duct through which sperm travels from the testicle to the urethra - to block it.
The blockage continues until heat applied to the blocked area causes the layers to mix, breaking them down and thereby unplugging the vas deferens.
The Chinese group say they tested this method in male rats by injecting four layers of materials into the vas deferens. In sequence, the injected layers were: a hydrogel that forms a physical barrier to sperm; gold nanoparticles that heat up when irradiated with near-infrared light; ethylenediaminetetraacetic acid (EDTA), a chemical that breaks down the hydrogel and also kills sperm; and one more layer of gold nanoparticles.
While in place, the liquid layers in the vas deferens prevented the male rats from impregnating females for more than 2 months, Wang's team reported Jan 30 in the journal ACS Nano.
But when the researchers shone a near-infrared lamp on the male rats for a few minutes, the layers mixed and dissolved, and the male rats were once again able to impregnate females. This offers "an effective and reversible manner to fill the gap of current medium-term contraceptive strategy" for men, the team said.
But, "though our method is promising, there is still a long way to go for practical practice," the Chinese team said. "More animal experiments are needed to verify the safety of materials," they said, and results in animals often fail to pan out in people.
One fertility expert in the United States agreed that much more study is needed.
"This study is a very preliminary look at injectable male contraception," said Dr Mary Rausch, of Northwell Health Fertility in Manhasset, New York. "Though this has a long way to go before it would be ready for trial or certainly use in humans, it would be a medical breakthrough if it did come to fruition.