Self-Made Microcapsules Hold Infinite Possibilities

Medical Device & Diagnostic Industry Magazine
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Originally Published MDDI August 2005

R&D Digest

Self-Made Microcapsules Hold Infinite Possibilities

Heather Thompson

Microcapsules that are smaller than living cells could be used to deliver imaging agents or drugs. The capsules are created using a mix- and-shake process that enables self-assembly.

The technique is different from traditional methods for creating drug-delivery capsules. And the capsules may be more shelf stable than those formed by other processes, too, says head researcher Michael Wong, PhD, who specializes in nanotechnology and materials chemistry at Rice University (Houston). “It really is a platform technology,” says Wong.

He explains that the microcapsules have a relatively thick shell—about 100–150 nm—that makes them very strong. “They are better able to resist drying, and they can withstand temperatures up to 70°C,” Wong says.

The capsules are a hybrid of a polymer and inorganic nanoparticles. For the basic design, Wong's team uses a polymer-and-salt solution mixed with nanosized silica particles. As the silica is introduced to the solution, a reaction occurs and the mixture creates hollow spheres. The process takes place in water, and any chemical or drug that is suspended in the water will get trapped inside the hollow spheres when they form.

The researchers plan to use the microcapsule development process for drug delivery. And they have numerous ideas for how to make the resulting devices. Some avenues they are exploring include using changes in pH or temperature to trigger the microcapsules to open and release drugs.

Imaging techniques involving contrast agents also hold possibilities for the microcapsules. Wong hopes that they can improve magnetic resonance imaging by protecting living cells from the normally toxic contrast agents. By delivering the contrast agents within the capsules, Wong says, damage to tissue and loss of the agent can be prevented.

The team also has plans to improve the microcapsules by making them multifunctional.

“Right now, we have microcapsules that are dumb,” Wong explains. “They just float around in water, but if we replace the silica with a material like iron oxide, then the capsule is magnetic.” Magnetic microcapsules could allow doctors to use magnets to precisely position drugs prior to their release.

Taking the idea further, Wong says using quantum dots (fluorescent nanoparticles) could make the capsules even more useful for drug delivery and imaging. “And if we mixed the two, we could build in even more functionality. We ultimately want smart capsules.”

The team has also done several experiments for encapsulating enzymes. Enzymes are extremely fragile and expensive, but protecting them from chemical reactions could mean that the enzymes could be used more than once. The Rice team has data showing that the enzymes are too large to leak through a microcapsule, but smaller molecules can pass through and enable the enzymes to act as a catalyst for chemical reactions.

There are many possibilities for the microcapsules, and Wong says the technology is ready for scale-up.
“I think they will be on the market very soon. Our technology is ready,” he says. “If a company asked us today to encapsulate Compound X, I believe we could have it ready in six months to a year.”

Halliburton Energy Services, Oak Ridge Associated Universities, Kraft Foods, and Rice University funded the research.

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