If I Only Had a Nano-Heart

Even on a cellular level, wound healing takes time. The body must target a large number of molecules called growth factors to just the right area to help repair the damage. Samuel Stupp, a chemist at Northwestern University in Evanston, Illinois, and colleagues wondered whether they could speed up the process by injecting a bit of nanotechnology into the mix. The new tools are molecules called peptide amphiphiles. Once injected into the body, the amphiphiles self-assemble into long, thin nanofibers, which hang out in the wound area.

After figuring out how to make the peptide amphiphiles, Stupp's team last year added eight amino acids, allowing the fiber to bind to a protein called heparin. Heparin in turn binds to growth factors that stimulate blood-vessel growth in natural wound healing. When the researchers injected a solution containing the amphiphiles into the corneas of mice--a standard model for testing new blood-vessel growth--the amphiphiles formed fibers that then prompted new blood vessels to grow.

To see whether the fibers could help animals recover from an actual injury, Stupp teamed up with Jon Lomasney, a molecular pharmacologist at Northwestern University Feinberg School of Medicine in Chicago, Illinois. The researchers induced heart attacks--and thus heart damage--in 20 mice. A half-hour later, they injected half of the mice with a solution containing their heparin-binding amphiphiles, while control animals received either an injection of growth factors alone or no treatment.

The growth factors quickly diffused away from the target area in the control animals. But in those given the amphiphiles, nanofibers assembled at the injury site and stayed put, drawing the body's own growth factors to the injury site. A month later, the team found that the hearts of the animals that received the amphiphiles pumped blood nearly as well as those of healthy animals. In contrast, the hearts of the control animals contracted about 50% less than normal. The same nanofibers also dramatically hastened wound healing in rabbits, the researchers reported here yesterday at a semiannual meeting of the American Chemical Society.

"It looks like great stuff," says Steven Zimmerman, a chemist at the University of Illinois, Urbana-Champaign, who helped organize the symposium. Stupp recently formed a company called Nanotope to help commercialize the technology.