Silk Stretches Drugs' Shelf Life To New Lengths

Jul 13, 2012
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This is SCIENCE FRIDAY. I'm Ira Flatow. This story is one of those aha moments when you hear about two totally unconnected items which find each other and solve an important problem. It's the story of the silkworm and the vaccine, which when combined could help vaccinate thousands of kids in hard-to-reach places.

To reach those kids, vaccines must travel in refrigerators and freezers up and down windy mountain paths or dirt roads. Ever schlep a refrigerator through a jungle? Well, then you know why. By some estimates, the money spent on keeping vaccines and antibiotics cold accounts for 80 percent of their price, and that's where the silkworm comes in because new research shows that the silkworm's cocoon, made out of silk, can serve as a cheap and effective to store the drugs from the killing heat.

Dr. David Kaplan Stern is professor and chair in the Department of Biomedical Engineering at Tufts University. He's also senior author of a study on this research in the Proceedings of the National Academy of Sciences. He joins us from Medford, Massachusetts. Welcome back to SCIENCE FRIDAY, Dr. Kaplan.

DR. DAVID KAPLAN: Thanks for having me back.

FLATOW: This is an interesting story. We've been - you know, how did you get to combine silk and vaccines and find a way to keep them from perishing in the heat?

KAPLAN: We had done some prior research, which showed proteins like enzymes and also hemoglobin were quite stable in silk-based materials from some other studies we were doing and therefore had led us to a series of studies over the last few years with vaccines, because of their inherent instability to heat, as well as antibiotics, to see if this protein matrix called silk would also stabilize this broader range of otherwise labile substrates. And it turned out that it does a pretty remarkable job in achieving that goal.

FLATOW: Give us an idea of the exact system that's going on there. What is going on inside the silk that protects the vaccine, the protein?

KAPLAN: We think in terms of mechanism, as we describe in the paper, there are very, very extensive networks of hydrophobic domains due to the basic chemistry of the silk protein that we use. And that's coupled with a very, very low water content that ends up in the materials once we form the silk into, for example, films, like a small piece of plastic film like you would normally see.

And this combination of features seems to really both entrap vaccines as well as essentially pin them to the silk substrate and prevent their denaturation and therefore their loss of activity.

FLATOW: So the vaccine gets sort of stuck in a nook and a cranny inside the silk?

KAPLAN: Correct, and there are so many nano-scale nooks and crannies in the silk that there's plenty of surface area for this kind of interaction.

FLATOW: And it protects it to high temperature?

KAPLAN: Yes, so the vaccines, the study we conducted over six months was up to 45 degrees centigrade, and we see again remarkable stabilization for the measles-mumps-rubella vaccine over that timeframe that otherwise, obviously, without the silk would be completely gone within a very short period of time.

And for the antibiotics, we showed this was in effect for extended periods of time, up to about 60 degrees centigrade.

FLATOW: And how soon can you get this out into the field?

KAPLAN: Well, that depends on a number of issues. I mean, we are a research lab. So we will depend on partners and, you know, corporate interactions to scale up the process and begin to go through whatever regulatory paths we'll need. So it'll take some time, but in terms of the data we have and the potential, we see things are really ready to go in certain directions quite quickly.

FLATOW: 1-800-989-8255 is our number. Is the idea to create a micro-needle of silk that both stores and delivers the vaccine so you have a delivery system, too?

KAPLAN: Yes, that's one of the modes we are considering and one of the more attractive ones, in fact, because if you think about it, during, sort of, the processing to make these vaccine-stable films, if you include micro-needle arrays on one side, and we've demonstrated this already, then you can have a sort of a pocket-carryable vaccine distribution system. And it would be fairly simple, low-cost and could be self-administered, depending on the specific needs. And this would open up obviously transport to all parts of the world, regardless of the availability of refrigeration.

FLATOW: Very interesting. So what makes silk such an interesting - I know you've been studying it for like 20 years, right?

KAPLAN: Correct.

FLATOW: And is there a difference in spider silk as opposed to the silkworm silk?

KAPLAN: There are many similarities between the two, as a family of proteins. There are also some distinct differences. There are many different kinds of both spider silks and silkworm silks. The silk we use for this particular study is really based on a purified version of what's present in the textile world, and we choose that because the infrastructure is there, the supplies are there to really utilize this in a widespread application like vaccine distribution that we're talking about.

FLATOW: So you could use it for more than just vaccines?

KAPLAN: Oh correct. Yes, it's used, as you said at the beginning, it's used in medical sutures forever, if you will, and newer medical products have been developed, as well. So there's a growing sort of domain of silk-based materials for a variety of medical needs coming along.

FLATOW: And as a way to store more than just vaccines and antibiotic?

KAPLAN: Oh, we anticipate that to be the case. We've demonstrated this with antibodies, monoclonal antibodies. I mentioned enzymes already. And so we anticipate quite a range of potential utility for therapeutics.

FLATOW: So you think this a game-changer for storing drugs?

KAPLAN: Well, we are very optimistic, yes. I think it could certainly have a major impact.

FLATOW: I want to thank you very much for taking time to be with us today, and good luck to you. It's very fascinating.

KAPLAN: Thanks very much.

FLATOW: David Kaplan Stern, professor and chair in the Department of Biomedical Engineering at Tufts University. He was a senior author on a study on this research in the Proceedings of the National Academy of Sciences. Transcript provided by NPR, Copyright NPR.