Reversible inhibition of sperm under guidance

Reversible inhibition of sperm under guidance (RISUG), formerly referred to as the synthetic polymer styrene maleic anhydride (SMA), is the development name of a male contraceptive injection developed at IIT Kharagpur in India by the team of Dr. Sujoy K Guha. Phase III clinical trials are underway in India, slowed by insufficient volunteers. It has been patented in India, China, Bangladesh, and the United States. A method based on RISUG, Vasalgel, is currently under development in the US.

RISUG works by an injection into the vas deferens, the vessel through which the sperm moves before ejaculation. RISUG is similar to vasectomy in that a local anesthetic is administered, an incision is made in the scrotum, and the vas deferens is injected with a polymer gel rather than being cut and cauterized. In a matter of minutes, the injection coats the walls of the vas with a clear gel made of 60 mg of the copolymer styrene/maleic anhydride (SMA) with 120 µl of the solvent dimethyl sulfoxide. The copolymer is made by irradiation of the two monomers with a dose of 0.2 to 0.24 megarad for every 40 g of copolymer and a dose rate of 30 to 40 rad/s. The source of irradiation is cobalt-60 gamma radiation.

The effect the chemical has on sperm is not completely understood. Originally it was thought that it lowered the pH of the environment enough to kill the sperm. More recent research claims that this is not enough to explain the effect.

...
Wikipedia