A reversible male contraception that uses magnets to target the testes.

Long-acting, reversible contraceptives are available for women, but most options for males are either single-use, such as condoms, or difficult to reverse, such as vasectomies. Researchers have discovered magnetic, biodegradable nanoparticles that reduced the likelihood of mice fathering pups for at least 30 days, paving the way for a safe, long-lasting, and reversible male contraception, according to ACS' Nano Letters.

Men's sperm count can be reduced by elevated temperatures, which can be induced by wearing too-tight pants or underwear. As a type of male birth control, some researchers have looked into more severe heating of nanoparticles injected into the testes.

However, the injection can be uncomfortable, the heating might cause skin injury, and the majority of nanomaterials studied thus far are not biodegradable. Weihua Ding, Fei Sun, and colleagues intended to create a safe and effective magnetic-thermal method of male contraception that didn't require injections into the testes.

The researchers used two types of biodegradable iron oxide nanoparticles that can be steered and heated using magnetic fields as male contraceptives. Polyethylene glycol (PEG) was used to coat one type of nanoparticle, while citric acid was used to coat the other PEG-coated nanoparticles could be heated to greater degrees, but they were more difficult to handle with magnets than the others. The researchers injected citric acid-coated nanoparticles into the circulation of mice for two days, then used magnets to direct the nanomaterials to the testes, where they were subsequently exposed to an alternating magnetic field for 15 minutes. The nanoparticles heated the testes to 104 degrees Fahrenheit, shrinking them and halting spermatogenesis for 30 to 60 days before gradually recovering. The mice couldn't father any pups for the first seven days following therapy, but by day 60, they were fathering roughly 12 pups per pregnant female. According to the researchers, the nanoparticles were non-toxic to cells and were gradually cleared from the body, opening up new possibilities for male contraception.