INTERNATIONAL HEALTH experts estimate that nearly half of all global vaccines are lost due to breakdowns in the cold chain. Even in industrialised nations, loss of drug efficacy at body temperature is a serious problem for advanced pharmaceutical delivery systems such as implantable drug-coated devices. The World Health Organisation estimates that unregulated temperatures at gaps in the chain account for the loss of half of all vaccines produced in the world, costing vaccine programmes approximately $200-300 million a year.
Most vaccines, enzymes, and antibodies and many antibiotics and other drugs require constant refrigeration from manufacture to delivery to maintain their effectiveness.
Vaccines and antibiotics are generally stored and transported cold, and lose their efficacy if not properly refrigerated at the right temperature at all points along the cold chain, from production to use. Keeping vaccines and antibiotics to small pouches of self-standing silk protein bio material can keep cold-sensitive drugs stable and eliminate the need for cold storage, like refrigeration because refrigeration and electricity are scarce and expensive in many countries.
Researchers at the Tufts University School of Engineering have 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 degrees F, by stabilising them in a silk protein made from silkworm cocoons. This could be a universal storage and handling system.
The low toxicity and price of silk make it a good candidate for application. Silk protein has a unique structure and chemistry that makes it strong, resistant to moisture, stable at extreme temperatures, and bio compatible, all of which make it very useful for stabilising antibiotics, vaccines and other drugs. The protein fibre of silk is composed mainly of fibroin and produced by certain insect larvae to form cocoons. The best-known type of silk is obtained from the Cocoon of the larvae of the mulberry Silk worm and Bombyx mori reared in captivity (Seri culture). Silk has a smooth, soft texture that is not slippery, it is one of the strongest natural fibres but loses up to 20% of its strength when wet. It has a good moisture regain of 11 per cent. Silk is resistant to most mineral acids, except for sulphuric acid, which dissolves it. It is yellowed by perspiration.
We can make silk into micro needles to deliver a vaccine is an enormously added advantage that can potentially provide a lot of useful solutions to stabilisation, distribution and delivery,” says Kaplan, who has been studying silk for two decades.
Jeney Zhang, a graduate student from Tufts University, working in the lab of silk maestro David Kaplan, showed that silk can stabilise two antibiotics – penicillin and tetracycline – as well as the measles, mumps and rubella (MMR) vaccine.
Wrapped in silk, penicillin spent a month at 60 degrees Celsius with no loss of activity. Normally, it breaks down after a few weeks at room temperature (25C), or just a day at human body temperature (37C) – a month at 60 is unheard of. Tetracycline is even more delicate. In silk, it lost 20 per cent of its activity after a month at 60C, and was unharmed at lower temperatures.
Silk stabilisation 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. Panilaitis earned his Ph.D. in biology at Tufts Graduate School of Arts and Sciences before joining Kaplan’s lab in 2001 as a post doctoral fellow.
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 percent of their initial potency.
How does silk protect is not clear yet, the researchers propose that silk protein may traps the vaccines viral particles in spaces between its ß-sheets, holding the particles in their native, folded state and preventing de naturation. Silks structure also excludes some water, enhancing its preservative qualities.