A reversible male contraceptive, targeted to the testes with magnets

The researchers tested two forms of iron oxide nanoparticles, which are biodegradable and can be guided and heated with magnetic fields, as male contraceptives. One type of nanoparticle was coated with polyethylene glycol (PEG) and the other with citric acid. Although the PEG-coated nanoparticles could be heated to higher temperatures, they were not as easily manipualated by magnets as the other ones.

So the researchers injected repeated doses of citric acid-coated nanoparticles into the bloodstream of mice for 2 days, guided the nanomaterials to the testes with magnets, and then applied an alternating magnetic field to the area for 15 minutes. The nanoparticles heated the testes to a temperature of 104 F, shrinking them and inhibiting spermatogenesis before gradual recovery 30 to 60 days after treatment. The mice couldn't father any pups 7 days after treatment, but they were back to fathering about 12 pups per pregnant female at day 60.

The nanoparticles were non-toxic to cells and were gradually eliminated from the body, offering new possibilities for male contraception, the researchers say.