Nanoparticle-studded capsules could have lots of purposes

Fatty molecules that make up the membrane surrounding, and compartments within, cells have been turned to a different purpose by University of Illinois researchers.

While structures created with lipid molecules aren't very stable normally, UI Professor Steve Granick's lab has found a way to "cover them with studs of nanoparticles that sort of armor them."

"You can treat them as if they were ... very durable objects," the materials science, chemistry and physics professor said recently.

Granick and graduate student Liangfang Zhang have employed the technique to create tiny capsules of biocompatible lipid molecules and filled the microscopic containers with fluorescent dye to test for leakage. None was detected.

That could make the capsules useful for delivering drugs to specific sites in the body or delivering DNA, proteins and other genetic material in gene therapies, for example. The capsules might even be linked together like tiny boxcars carrying a variety of materials, perhaps some that don't normally exist and function outside the cell membrane.

With other reactive molecules attached to their surface, the capsules also could be employed as molecular-scale sensors to detect, say, toxins or tumors.

"We haven't done any of that yet, but this opens the door to doing it," said Granick, a professor at the UI's Materials Research Laboratory and Beckman Institute.

Granick said the capsules also might be used as cargo carriers in plants as well as people, of potential importance in an agricultural state like Illinois.

In addition, he said they could be useful to scientists, as sort of super small fish bowls in which to contain other molecules and study their interactions.

The problem with structures made from untreated lipid molecules is that lipids naturally want to bump into each other, stick together and make bigger conglomerations, which makes it hard to maintain the capsule-sized units.

"They love to combine with one another," Granick said. "You don't want them coalescing."

But Zhang, who's studying chemical engineering, found that lipid structures could be stabilized at a certain size by studding them with nanoparticles.

"It turned out to work very well," Granick said. "No one had tried before and he had no idea if it would work."

It worked so well that the UI researchers are two years ahead of where they expected to be at this time.

"Now we want to use them," Granick said.

The researchers create the capsules in solution via the lipids' natural tendency to self-assemble, fill them with a cargo, or attach other molecules to their surface. They then introduce the nanoparticles, which carry a charge that attracts them to, and makes them adhere to, the lipid structures.

In effect, the nanoparticles act as bumpers, preventing the lipids from contacting and coalescing, Granick said. Since the particles don't cover the entire surface, they leave gaps that can be used as paths to let out whatever cargo is inside or as spaces where other molecules get attached to the outside.

The technique was outlined online recently ahead of publication in the American Chemical Society journal Nano Letters. The U.S. Department of Energy funded the research.

Having shown it's possible to make stable capsules and contain dye inside them, Granick and colleagues are working now on other techniques that could allow the vessels to be put to use.

The UI researchers still have to test the nanoparticles for biocompatibility. But they've successfully used a variety of types, from latex to silica and both positively and negatively charged, so it shouldn't be difficult to identify particles that can be safely used in the body, Granick said.

Among other things, his lab also is studying how the capsules, once they reach an intended location, might be directed to release their contents.

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