Chinese researchers have developed an experiment cocktail-inspired male birth control method that is long-lasting, effective and reversible.

For decades, women have shouldered most of the burden of contraception. However, long-term use of female birth control pills could increase the risk for side-effects such as blood clots or breast cancer. Common forms of male contraception are either short-term (condoms) or long-term (vasectomy). However, condoms can fail and vasectomies, while effective, are not often reversible. 

Now, a team from the Nanchang University developed a new method that involves injecting four layers of materials into the vas deferens -- the duct in the male reproductive system that conveys sperm from the testicle to the urethra. The layers are injected sequentially, beginning from a hydrogel that forms a physical barrier to sperm; gold nanoparticles, which heat up when irradiated with near-infrared light; an ethylenediaminetetraacetic acid (EDTA), a chemical that breaks down the hydrogel and also kills sperm; and finally, another layer of gold nanoparticles. 

The injected materials kept the rats from impregnating females for more than 2 months. However, when the researchers shone a near-infrared lamp on the rats for a few minutes, the layers mixed and dissolved, allowing the animals to produce offspring. "Inspired by cocktails, we designed a medium term (2-20 weeks) male contraceptive strategy. Through a sequential injection process of four reagents, physical clogging of the vas deferens and chemical inhibition of the sperm motility were realised simultaneously," said Xiaolei Wang from the University.

"The contraceptive period could be directly preset by adjusting the injection ratio of each reagent," Wang said. The method, reported in the journal ACS Nano, was inspired from cocktails, such as the Galaxy, that bartenders make by layering colorful liquids in a glass. If the beverage is stirred or heated, the layers combine into a uniform liquid. 

Similarly, applying heat would cause the injected layers of materials to mix, breaking them down and "unplugging the pipeline", Wang noted. While previous attempts to create a male pill have resulted in side effects such as liver damage or low sex drive, the researchers say that this pilot experiment is promising. However, more research is needed to verify the safety of the materials.