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.

arm
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 chargeIllustration by Todd Detwiler
Biodome
Biodome
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.Illustration by Todd Detwiler
Ion Flood
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.Illustration by Todd Detwiler
Gene Trigger
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.Illustration by Todd Detwiler
New 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.Illustration by Todd Detwiler

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