Hard-boiled eggs

There are many methods of female contraception, but only two methods are available to men: barrier (condoms) and vasectomy; both have their drawbacks.

Condoms are among the most affordable and simple methods of contraception, and also protect against sexually transmitted infections, but they can break. In addition, some men are allergic to latex, which is part of standard condoms. Vasectomy is a surgical procedure that can be painful and involves risks accompanying any surgical intervention. Another disadvantage of vasectomy is the irreversible effect.

Thus, the search for alternative options for male contraception is justified, and one of the methods that is currently being investigated is nanocontraception.

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The principle of nanocontraception is to deliver nanoparticles – in this case, about 100 nanometers in diameter – to the testicles, followed by heating. As the researchers suggest, the ability to raise the temperature of the testicles in a controlled manner will become a way to "turn off" sperm production at will, because when heated, the number of spermatozoa in them decreases. But this process requires caution – excessive heating can irreversibly destroy the ovarian tissue, and spermatogenesis will not recover even when the temperature normalizes.

Nanotechnology for local testicular heating was first used in mice in 2013 by biologist Fei Song and his multidisciplinary research team from the University of Toronto. Their early experiments involved injecting nanoparticles directly into the testicles of mice.

These nanoparticles were nanorods of gold atoms coated with several long polymer chains of ethylene glycol. Infrared radiation was used to heat the testicles, which increased the temperature of the nanoparticles from about 30°C to 37-45 °C, depending on the concentration of the injected nanoparticles and the intensity of the radiation.

This exposure to mice resulted in thermal damage to the skin covering the testicles, so the team concluded that it was painful for the animals, although there was no reliable way to measure the level of pain. The researchers continued to search for other ways of introducing and heating nanoparticles.

Iron rods

In the new study, Sun's group developed nanorods made of magnetic iron oxide and coated them with citric acid, retaining the same size and shape as the rods of the first generation.

These magnetic nanoparticles were injected intravenously into mice, and then a magnet was placed next to the gonads of the animals for four hours, which facilitated the movement of nanoparticles to the testicles. This procedure – injection followed by magnetic guidance – was carried out daily for 1-4 days. After that, an inductor coil was wound over the testicles of the mice, through which an electric current was passed. A magnetic field was formed, which heated the nanoparticles and, consequently, the testicles.

This method gave a similar increase in temperature to the previous one – from the initial level of 29 °C to 37-42 °C. The more days the mice were injected with nanorods, the higher the temperature in the testicles at the end of the experiment.

Heating of the testicles led to their shrinkage and extinction of function, but if the temperature did not exceed 45 ° C, a gradual recovery was noted 30 and 60 days after treatment. Fertility decreased, and in some cases was completely absent seven days after treatment, but then gradually, although not completely, recovered. 

Although fertility did not reach the initial level, there was no noticeable difference in the size of the litter of females fertilized by mice involved in the experiment; none of the cubs born had morphological defects.

Sun and his colleagues found that, unlike gold particles that remained indefinitely in the testicles of mice, iron nanorods gradually entered the liver and spleen, and then were completely eliminated from the body.

Birth planning

The cost and irreversibility of surgical castration make many pet owners look for alternative methods of contraception. Nanocontraception, according to the authors of the study, is ready for use on pets, moreover, this method is already used on cats in China.

The ultimate goal of the researchers is human contraception, but this will require detailed studies to confirm the safety of the method for men. In addition, it is necessary to modify the method of delivery of nanoparticles to the testicles.

Article W.Ding et al. Magnetic Testis Targeting and Magnetic Hyperthermia for Noninvasive, Controllable Male Contraception via Intravenous Administration is published in the journal Nano Letters.

Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on The Conversation: Great balls of fire: How heating up testicles with nanoparticles might one day be a form of male birth control.