Frogs Can Regrow Lost Legs in the Lab. Now, Researchers Say Human Limb Regeneration Could Happen ‘in Our Lifetime’

A 24-hour treatment using a five-drug cocktail kickstarted a yearlong regrowth process in the amphibians

the underside of a spotted yellow frog called an African clawed frog against a black background
African clawed frogs (Xenopus laevis) were able to regrow a functional limb within 18 months of the novel treatment. Paul Starosta via Getty Images

Just a handful of animals are able to naturally replace lost limbs, including some salamanders, starfish, and axolotls. In the wild, an African clawed frog can’t regrow a missing appendage. But now, a new experimental technique is helping the amphibians replace their lost body parts, and scientists hope their work could someday make human limb regeneration possible.

In the study recently published in Science Advances, researchers at Tufts and Harvard University first amputated the leg of an adult female African clawed frog, and then coated the stump with a special five-drug cocktail. They let the wounds soak in the solution for the next 24 hours. Then, over the next year and a half, the adult frogs regrew a functional leglike structure with nerves, muscles, bones, and toelike projections. 

"It's exciting to see that the drugs we selected were helping to create an almost complete limb," study author Nirosha Murugan, a biologist at Tufts University, says in a statement. "The fact that it required only a brief exposure to the drugs to set in motion a months-long regeneration process suggests that frogs and perhaps other animals may have dormant regenerative capabilities that can be triggered into action."

Animals, like lizards, that can regrow limbs use stem cells at the end of the wound to rebuild their lost appendage, per USA Today’s Jordan Mendoza. But like humans, African clawed frogs can’t regrow complex limbs and instead heal the wound with scar tissue.

To stimulate the growth of a leg, the scientists applied a silicone cap they called “BioDome,” to each frog's wound. Each cap contained a mixture of five drugs including hormones to encourage nerve and muscle growth and another to prevent the frogs' bodies from producing collagen, which leads to scarring, per Live Science’s Patrick Pester. The thimble-like cap mimicked the fluid-filled sac where embryos develop.

"Using the BioDome cap in the first 24 hours helps mimic an amniotic-like environment, which, along with the right drugs, allows the rebuilding process to proceed without the interference of scar tissue," study author David Kaplan, an engineer at Tufts, says in a news release.

The frogs’ regenerated limbs were functional, but not perfect. Their new appendages lacked toenails and some webbing, but the frogs were able to use their new leg to swim.

“It’s not a full limb that’s regrown,” says Kelly Tseng, a biologist studying regeneration at the University of Nevada, Las Vegas, who was not involved with the research, to Sabrina Imbler for the New York Times. “But it’s certainly a robust response.”

Next, the research team is trying out their technique on mice, which they expect will present new challenges. Despite the obstacles ahead, the success of the experiment African clawed frogs makes Murugan believe she’ll see similar applications for humans within decades.

"The biomedical engineering aspect is actually making these new advancements to kind of understand and fix biology. And I think that integration is going to make this happen in our lifetime," Murugan says to Morgan McFall-Johnsen for Business Insider.

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