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Drug Development

Contraceptive candidate acts by blocking sperm

Early human test results show a hydrogel implant occludes the vas deferens

by Laurel Oldach
January 4, 2024


An illustration shows how a double-barreled injector mixes two solutions at the point of injection. The drawing also shows a gel blocking an anatomical tube.
Credit: Contraline
A specialized injector mixes two solutions at the point of injection to polymerize in place in the vas deferens.

For decades, there have been many contraceptives marketed to women but few options marketed to men —single-use condoms or permanent vasectomy. Now, Virginia-based biotechnology company Contraline is announcing preliminary results from its first trial in humans of a technology it hopes will fill the gap: a hydrogel implant that stops sperm from escaping the body, but not permanently.

The implant works by blocking the vas deferens, the same duct that is cut during a vasectomy. The device relies on a hydrogel that forms when two aqueous solutions are injected during a 20 min procedure. Once mixed, the solutions polymerize and form a gel with pores too small for sperm to pass through. The company says in a press release that in the first test of the product on 23 men in Australia, sperm count was reduced by 99–100% 1 month after implantation. Contraline CEO Kevin Eisenfrats says the gel lasts roughly 2 years in animal studies and can be degraded earlier on demand, though that has yet to be tested in humans.

Contraline has not disclosed its chemistry. While the company holds a patent describing a polyethylene glycol gel cross-linked by thiol-maleimide reactions, independent chemists whom C&EN contacted were unwilling to comment on the work without a peer-reviewed publication to refer to. Some concerns to watch out for with any hydrogel implant, they note, are off-target reactions with tissues and an inflammatory response.

The concept of using a gel to block the vas deferens is not new. In the 1970s, researchers in India developed a copolymer of styrene and maleic anhydride to stop sperm (Contraception 1979, DOI: 10.1016/0010-7824(79)90052-0). Although the implant seemed to be effective in a trial with more than 130 participants (Indian J. Med. Res. 2019, DOI: 10.4103/ijmr.IJMR_635_18), it has yet to reach patients commercially. According to Eisenfrats, that’s because of a few chemical drawbacks: the reactants must be injected in an organic solvent, and it is unclear whether the procedure can be reversed.

Others aren’t ready to write off the styrene–maleic anhydride approach. US-based biotechnology company Next Life Sciences is developing an updated formulation after what its CEO describes in an email as “a rigorous effort to refine the hydrogel formulation for performance, consistency, and scalability.”The company says it’s planning for clinical trials of the new hydrogel to begin soon.



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