Let Them Wear Silk

Feb. 15, 2013

By Medical Discovery News

While parents of school-aged children may feel the list of required vaccinations to be rather long, the truth is there are relatively few vaccines to combat the myriad of infectious diseases, which are the leading cause of death in the world today. However, scientists are working to develop vaccines that protect against many infectious agents and even cancer and drug addiction. 

The Achilles heel of modern vaccines is their dependence on constant refrigeration, because they are not stable at room temperature and are even more fragile at body temperature. Stabilizing vaccines and other drugs to non-refrigerated temperatures has been an intense focus of many researchers for several decades. 

If vaccines did not need to be refrigerated, they would be more accessible during natural disasters like hurricanes or earthquakes and easier to use in developing countries. In industrialized countries, almost half of all vaccines are rendered unusable because they have not been kept at cold temperatures, which results in them losing potency. 

But researchers may have found the answer to this dilemma in a surprising source – one more often seen on the label of fancy clothes than in a shot. A team at Tufts University found that encasing vaccines or other therapeutic drugs in silk prevents them from being affected by extreme changes in temperature.

Silk comes from insects that produce it, mostly to make cocoons where they complete metamorphosis from larvae to adult moths. The shimmer of silk comes from the prism-shaped structure of its fibers and allows it to refract light, which first attracted the eye of a Chinese empress in 2600 BC who decided to learn a way to weave it into cloth, according to Asian legend. Some of same qualities of silk have also made it a tool in protecting vaccines.

The protein that comprises silk has some unique properties: strength, moisture resistance, biocompatibility, and temperature resistance. In a purified state, it forms sheets with strands of cross-linked amino acids and pockets that serve as locations for vaccines and drugs to be introduced. In dried preparations, this protected location shelters vaccine and drug molecules from moisture and stabilizes them to changes in temperature.

For example, the mumps, measles and rubella (MMR) vaccine was stable up for to six months at body temperature and even at 140degrees for an extended period of time. This protection from heat also worked for two commonly prescribed antibiotics, penicillin and tetracycline. At 140 degrees, the tetracycline encased in silk only lost 10 percent of its antibacterial activity, compared to an 80 percent loss without silk. And penicillin did not lose any of its potency after 30 days in silk, compared to a complete loss at the same temperature without silk. 

This extended stability will prevent waste, lead to more effective use of precious antimicrobials, and potentially help with the antibacterial resistance problems experienced today. In addition, “wearing” silk could also work for other biological agents and drugs.

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