Silk-Wrapped Drugs Stay Potent Longer
Encasing drugs in silk-film tabs can keep them potent even without refrigeration, one team of engineers found. The tabs can help deliver temperature-sensitive medicines to regions without good infrastructure to keep things refrigerated.
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Just as caterpillars encase themselves in silk to protect them while they're metamorphosing, a silk wrapping may help protect medicines from losing their potency, according to a new study. The new research sought to improve the stability of drugs that normally work only if they're kept cool. Trapping drugs in thin tabs made of purified silk proteins may keep them as potent as refrigeration does, a team of engineers found. "The silk coats the vaccine and then prevents it from losing potency," said David Kaplan, a Tufts University bioengineer who led the research.
Silk-packaged vaccines and antibiotics may be especially helpful in developing countries that don't have the infrastructure to keep drugs refrigerated during every step of the journey from manufacturer to clinic, Kaplan and his colleagues wrote in a paper detailing their research, published today (July 9) in the journal Proceedings of the Natural Academy of Sciences. Even in developed countries, doctors' offices sometimes throw out vaccines that get left out too long. Silk proteins added to drugs may help reduce that waste.
To see if silk helps keep temperature-sensitive drugs active at warmer temperatures, researchers encased one vaccine and two antibiotics in small squares of a thin film they developed using proteins that domesticated silkworms make. The scientists stored their silk tabs at different temperatures, then later tested the drugs' potency after dissolving the silk film.
They found that silk-treated medicines maintained their potency as well or better than the same drugs preserved in other ways, including freeze-drying and storing in a film of collagen. A silk-coated measles, mumps and rubella vaccine stayed 85 percent potent after six months at 98.6 degrees Fahrenheit (37 degrees Celsius), for example, while a powdered measles vaccine only maintained about 10 percent of its potency at that temperature. The silk film kept penicillin 100 percent active for 30 days at 140 degrees Fahrenheit (60 degrees Celsius) and kept the antibiotic tetracycline 90 percent active for 14 days at 140 degrees Fahrenheit. [Tobacco Plants Turn into Living Vaccine Factories]
"I think all of the data at high temperatures (40-60 C) for these compounds is quite remarkable and suggests this is a very robust and useful technology," Kaplan wrote in an email to InnovationNewsDaily.
The silk film works by cradling the active molecules in medicines in tiny, nano-size pockets. The pockets help the molecules maintain their shape, which is crucial for their activity. The pockets also seal away water, which can alter a molecules' shape.
In the future, if researchers develop the silk film further, Kaplan said he imagined it might be used in three ways. Doctors might dissolve the film and give medicines, silk and all, to patients. Clinical-grade, purified silk doesn't elicit a strong immune reaction from the body and is already used in some sutures. Researchers could also develop a way to separate the silk proteins from the medicine, so they would administer only the medicine.
"The third way, my favorite, would be like a Band-Aid," Kaplan said in a later interview with InnovationNewsDaily. He imagines a silk stick-on strip that has tiny needles on its sticky surface. The needles would puncture the skin in a way that the patient couldn't feel and deliver the strip's vaccine contents underneath the skin.
Kaplan, who has been studying silk for more than 20 years, previously found that silk film tabs kept other biological materials — including enzymes, antibodies and blood protein called hemoglobin — stable and fresh. Because the tab method works so well with so many different biological substances, it may become a universal packaging for stabilizing drugs, he said.