Vas-occlusive contraception

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Vas-occlusive contraception is a male method that blocks sperm from moving through the vas deferens, the tubes that carry sperm from the testicles to the urethra. Researchers have studied many approaches, both reversible and irreversible, to offer alternatives to vasectomy and to hormone-based contraception. Here are the main ideas and examples:

- Intravasal devices (valves, plugs, threads)
- Intravasal control valve (ICV): a reversible valve placed in the vas deferens that can block or allow sperm flow depending on its position. Bionyx has a T-shaped valve made of gold and stainless steel; turning a perforated ball inside the T can stop or let sperm through. It requires microsurgery to implant.
- Intravasal thread (IVT/IVD): a device inserted in the vas deferens that blocks sperm transport mechanically; removing it can restore sperm flow. Results vary by animal studies and humans; in humans, a urethane-coated nylon version reduced sperm counts but did not guarantee complete sterility.

- Chemical occlusion (injections)
- Many chemical mixes have been tried to block the vas deferens by scarring the wall. A notable combination of carbolic acid and n-butyl alpha cyanoacrylate produced high rates of azoospermia and pregnancy prevention, but is irreversible and not always permanently occlusive (about 4% failure in some studies). Ethanol and formaldehyde injections have also caused sterilization but are irreversible.

- Injectable plugs (MPU) and non-injectable plugs
- Injectable polyurethane plugs (MPU) can create azoospermia in many men, but the effect typically appears after about 24 months. In studies where the plug was removed within five years, fertility often returned.
- Shug (silicon plug) is a non-injectable plug made of two silicon plugs with nylon tails to anchor it in the vas deferens. It requires surgical insertion and removal. Trials showed a large drop in sperm motility, but this approach has had limited research and isn’t as effective as a vasectomy.

- Adaptive devices and other methods
- RISUG (a trademark for Reversible Inhibition of Sperm Under Guidance): a non-toxic polymer gel injected into the vas deferens that blocks or deactivates sperm, leading to infertility within about 10 days. Its exact mechanism is not fully known, but the gel partially occludes the duct and neutralizes passing sperm. RISUG has been studied in India and is in Phase III clinical trials there.
- Vasalgel: inspired by RISUG, it uses a different polymer (styrene maleic acid) in dimethyl sulfoxide. It aims for a longer shelf-life and simpler production. It has shown azoospermia in rabbits and restored flow after removal in studies. In 2023, the patent was acquired by NEXT Life Sciences, which plans to commercialize it as Plan A for Men.

- New and ongoing efforts
- ADAM by Contraline: an injectable, aqueous-based hydrogel designed for the vas deferens. It is inserted through a minimally invasive procedure and uses ultrasound guidance for delivery. Clinical trials began in 2022.
- Overall, vas-occlusive methods are expected to have side effects similar to vasectomy, but are being developed to offer safer or reversible options.

In short, many approaches are being explored to stop sperm from reaching the outside world, with options ranging from reversible valves and mechanical threads to chemical and gel-based occlusions. Some strategies may be reversible, while others are designed to be permanent or require removal to restore fertility.