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Reported by: Dr. Venkat S. Karra, Ph.D.

Most vaccines, enzymes, and antibodies and many antibiotics and other drugs require constant refrigeration from manufacture to delivery to maintain their effectiveness. A serious obstacle to the effective use of life-saving pharmaceuticals is keeping them cold. International health experts estimate that nearly half of all global vaccines are lost due to breakdowns in the “cold chain.”

Tufts biomedical engineers team led by David L. Kaplan, PhD, has discovered a way to maintain the potency of vaccines and other drugs—that otherwise require refrigeration—for months and possibly years at temperatures above 110 F, by stabilizing them in a silk protein made from silkworm cocoons. They found that silk stabilization preserved the efficacy of the measles, mumps and rubella (MMR) vaccine, as well as penicillin and tetracycline, at a wide range of temperatures (at least up to 60 C or 140 F) significantly better than other options such as collagen encapsulants, dried powders, and solutions.

“Silk protein has a unique structure and chemistry that makes it strong, resistant to moisture, stable at extreme temperatures, and biocompatible, all of which make it very useful for stabilizing antibiotics, vaccines, and other drugs. Importantly, the pharmaceutical-infused silk can be made in a variety of forms such as microneedles, microvesicles, and films that allow the non-refrigerated drugs to be stored and administered in a single device.

Measles is one of the leading killers of children worldwide. Without refrigeration, the MMR vaccine rapidly loses potency. But after six months of storage in freeze-dried silk films at body temperature (37 C) and at 113 F (45 C), all components of the vaccine retained approximately 85% of their initial potency. Silk-stabilized antibiotics also retained high activity.

Storage in silk films at body temperature resulted in no activity loss for tetracycline, compared with an 80% loss within four weeks of storage in solution. Even for films stored at 140 F (60 C), tetracycline activity loss was only 10 percent after two weeks, compared with 100% loss after two weeks of storage in solution.

No activity loss was observed for penicillin stored in silk films at 60 C for 30 days; in contrast, total activity loss was observed within 24 hours when penicillin was stored in solution at the same temperature. Silk stabilization also protected the tetracycline against degradation by light, a benefit that the researchers did not anticipate, according to co-author and research assistant professor Bruce Panilaitis. So far, Panilaitis adds, the researchers haven’t found any pharmaceutical that they have been unable to stabilize. This could be a “universal storage and handling system.”

The research will be published in the Proceedings of the National Academy of Sciences (PNAS).

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