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Glass proteins shatter dehydration protocols

07/12/2010
Erin Podolak

Researchers have developed a dehydration method that preserves proteins in a glass state, which can improve protein-based drug delivery and protein preservation.

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A new dehydration method preserves proteins in a glass state, which may improve protein-based drug delivery mechanisms and protein preservation methods. The protocol, developed by researchers from Duke University’s Department of Mechanical Engineering and Materials Science, is the first to use dehydration to form protein-based glass microdroplets.

In addition to proteins, the new method could be used to dehydrate other molecules, including salts, sugars, DNA, polymers, and other water-soluble small molecules, like prescription drugs. Previous drug delivery systems, such as those utilizing frozen or powdered proteins, have a tendency to clog syringes, impeding delivery.

A glassified protein microdroplet. Source: Duke University


“In the freeze-drying process itself, some very sensitive biologic drugs can also get damaged," David Needham a professor of mechanical engineering and materials science at Duke University’s Pratt School of Engineering who worked on the research, said in a press release. “Freeze-drying proteins into solids is also slower and more expensive than glassifying them and the resulting flaky powder is harder to handle than glassified beads.”

The new method removes virtually all the water from around a dissolved protein by using energy currents and controlled water activity (Aw) to pull the water molecules into a second solution. "It's like a sponge sucking water off a counter," said Needham.

Only water molecules that are essential to the protein’s molecular structure remain in the glassified proteins. This small amount of water is not enough to support the growth of bacteria or fungi, and allows the glassified proteins to regain their original functions after rehydration. This makes the glassification of protein microdroplets a promising method for protein preservation.

The team tested their method with the enzyme protein lysozyme. Microdroplets were formed by inserting a micropipet loaded with lysozyme solution into a chamber filled with decanol, a drying agent. Applying pressure to the micropipet, researchers released a microdroplet of lysozyme solution into the decanol and then reattached it on the end of the micropipet by suction. Under diffusion-controlled dissolution, the droplets hardened within 30 minutes and were then released a second time to settle on the bottom of the chamber.

The choice of decanol was an important to method’s success, said Needham. Decanol does not dissolve in water, but water does dissolve in decanol. This allowed the researchers to use the solvent as a drying agent, removing the water from the solution and away from the protein.

Needham’s team is working with Duke University’s Brain Tumor Center and Comprehensive Cancer Center to secure additional funding to study the glass microdroplets as drug delivery systems for the cancer drugs O6-AMBG, lapatinib, and shepherdin.

Needham has formed a company called Biogyali (in Greek, gyali means glass) to develop this technology for commercial purposes. The researchers plan to further develop the glass microdroplets, specifically experimenting with a time-release component by encasing the microdroplets in a polymer that would biodegrade over time to release a certain drug.

Funding for the research was provided by the National Institutes of Health. The paper, "Hydration potential of lysozyme: protein dehydration using a single microparticle technique," was published in the March edition of Biophysical Journal.