Monday, March 12, 2007

TR10: Nanohealing

Tiny fibers will save lives by stopping bleeding and aiding recovery from brain injury, says Rutledge Ellis-Behnke.

By Kevin Bullis

Rutledge Ellis-Behnke Credit: Asia Kepka

Multimedia •  View a slideshow of Ellis-Behnke's work.

This article is one in a series of 10 stories we're running this week covering today's most significant emerging technologies. It's part of our annual "10 Emerging Technologies" report, which appears in the March/April print issue of Technology Review.

In the break room near his lab in MIT's brand-new neuroscience building, research scientist Rutledge Ellis-Behnke provides impromptu narration for a video of himself performing surgery. In the video, Ellis-Behnke makes a deep cut in the liver of a rat, intentionally slicing through a main artery­. As the liver pulses from the pressure of the rat's beating heart, blood spills from the wound. Then Ellis­-­Behnke covers the wound with a clear liquid, and the bleeding stops almost at once. Untreated, the wound would have proved fatal, but the rat lived on.

The liquid Ellis-Behnke used is a novel material made of nanoscale protein fragments, or peptides. Its ability to stop bleeding almost instantly could be invaluable in surgery, at accident sites, or on the battlefield. Under conditions like those inside the body, the peptides self-assemble into a fibrous mesh that to the naked eye appears to be a transparent gel. Even more remarkably, the material creates an environment that may accelerate healing of damaged brain and spinal tissue.

Ellis-Behnke stumbled on the material's capacity to stanch bleeding by chance, during experiments designed to help restore vision to brain-­damaged hamsters. And his discovery was itself made possible by earlier serendipitous events. In the early 1990s, Shuguang Zhang, now a biomedical engineer at MIT, was working in the lab of MIT biologist Alexander Rich. Zhang had been studying a repeating DNA sequence that coded for a peptide. He and a colleague inadvertently found that under certain conditions, copies of the peptide would combine into fibers. Zhang and his colleagues began to reëngineer the peptides to exhibit specific responses to electric charges and water. They ended up with a 16-amino-acid peptide that looks like a comb, with water-loving teeth projecting from a water-repelling spine. In a salty, aqueous environment--such as that inside the body--the spines spontaneously cluster together to avoid the water, forming long, thin fibers that self-assemble into curved ribbons. The process transforms a liquid peptide solution into a clear gel.

Originally, Ellis-Behnke intended to use the material to promote the healing of brain and spinal-cord injuries. In young animals, neurons are surrounded by materials that help them grow; Ellis-Behnke thought that the peptide gel could create a similar environment and prevent the formation of scar tissue, which obstructs the regrowth of severed neurons. "It's like if you're walking through a field of wheat, you can walk easily because the wheat moves out of the way," he says. "If you're walking through a briar patch, you get stuck." In the hamster experiments, the researchers found that the gel allowed neurons in a vision-related tract of the brain to grow across a lesion and reëstablish connections with neurons on the other side, restoring the hamster's sight.