From individual proteins to whole tissues, scientists have been engineering or growing biological mimics for a variety of medical and industrial applications. Bioengineers from the Institute for Medicine and Engineering (IME) at the University of Pennsylvania have designed an artificial capsule that imitates many of the qualities of natural cells. The capsule - dubbed a polymersome - has wide-ranging possibilities, from a new gene-therapy delivery vehicle to an artificial red blood cell. The collaborative study between IME and the University of Minnesota describes the physical properties of the capsules. The team's findings appear in the May 14 issue of Science.
"We've created an entirely new type of synthetic capsule," says co-senior author Daniel Hammer, Ph.D., professor of chemical engineering. "The polymersomes are the same size as natural cells, but their outer membrane is much tougher than the phospholipid membrane of biological cells. And, they have the capacity to be undetectable by the human immune system so could be used to deliver all kinds of therapies to specific targets."
The capsules were produced using block copolymer chemistry. A carbon-based polymer and an organic solvent are dried on a wire. Then water is added to the system and the wire is zapped with electricity. Over time, as the polymer film lifts off the wire's surface, capsules automatically form.
"Using this method we've been able to make capsules the size of natural cells from synthetic polymers, which has never been done before," notes Dennis Discher, Ph.D., co-senior author and assistant professor of mechanical, chemical, and bioengineering. The largest artificial cell made prior to these are a micron in diameter, whereas the polymersomes range from 10 to 35 microns. Most human cells are 10 microns.
Polymersomes are also biocompatible. A chemical tag made from polyethylene
oxide is used to make lipid capsules and other biological delivery vehicles
Contact: Karen Young Kreeger
University of Pennsylvania School of Medicine