How to grow an arm

Using tiny electrical currents to go from stump to fully functioning appendage

This article explains a theoretical limb regeneration process being developed by bioengineer Michael Levin. Read our profile of him here.

Severed Arm

Surgeons prepare an amputation site for limb ­regeneration by cleaning the wound site of debris. They then expose raw nerves, bones, ­tendons, muscles, and other tissues so the molecules in them can be treated with a faint electrical charge


To conduct electrical currents, the wound site must remain moist and protected from air, which would dry it out and expose the wound to infection. So surgeons put this sleeve over the site. Made of silicone, rubber, and silk, it mimics the aquatic habitat of a womb.

Ion Flood

The sleeve contains drugs that can manipulate the body’s ion channels, hollow proteins that sit on the surface of cells letting charged molecules move in and out, thus changing a cell’s charge and its signaling to other cells across the body.

Gene Trigger

The cells’ bioelectric signals influence the action and direction of genes, acting as a sort of software code for the entire body. Once the signal to divide cells is given, a cascading effect happens, and the body will begin the natural process of growing an arm.

New Arm

The process is as fast as normal human fetal growth. That means a 25-year-old solder who lost an arm to a roadside bomb would have to wait a decade, until the age of 35, for the arm of a middle-schooler—but one that would be fully functioning.

This article was originally published in the January/February 2017 issue of Popular Science, under the title “How To Grow An Arm.”

Rachel Feltman

Rachel Feltmanis the Executive Editor of Popular Science and the host of the podcast The Weirdest Thing I Learned This Week. She's an alum of Simon's Rock and NYU's Science, Health, and Environmental Reporting program. Rachel previously worked at Quartz and The Washington Post. Contact the author here.