International health experts
estimate that nearly half of all global vaccines are lost due to breakdowns in
the "cold chain." Even in industrialized nations, loss of drug efficacy at body
temperature is a serious problem for advanced pharmaceutical delivery systems
such as implantable drug-coated devices. 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 programs 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 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%. 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 enormous 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 vaccine’s viral particles in spaces between its β-sheets,
holding the particles in their native, folded state and preventing de naturation.
Silk’s structure also excludes some water, enhancing its preservative qualities.