RISUG consists of injecting a polymer gel, styrene maleic anhydride in dimethyl sulfoxide, into the vas deferens. The polymer has a positive charge, and when negatively charged sperm pass through the vas deferens, the charge differential severely damages the sperm.[5] A second injection washes out the substance and restores fertility. As of 2011[update], RISUG is in Phase III of human testing in India and has been patented in India, China, Bangladesh and the United States.