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Biomedical Engineering

The Biomedical Engineering blog is the place for conversation and discussion about topics related to engineering principles of the medical field. Here, you'll find everything from discussions about emerging medical technologies to advances in medical research. The blog's owner, Chelsey H, is a graduate of Rensselaer Polytechnic Institute (RPI) with a degree in Biomedical Engineering.

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Silk’s Not Just for Neckties

Posted June 13, 2016 1:34 PM by BestInShow

With so many novel advanced materials making news these days – like graphene in all its permutations – I was pleased to discover that silk, a material that dates back to ancient times, has many 21st-century uses. Researchers at Tufts University’s Silk Lab, at MIT, North Dakota State University, and elsewhere are contributing novel applications for silk proteins.

Where does silk come from?

Silk comes from silkworm spit. Doesn’t that just make you want to run out and buy a set of silk PJs? Seriously, if you ask most people where they think silk comes from, they’d answer it comes from the cocoons of mulberry silkworms (Bombyx mori) cultivated expressly for textiles. (And their cocoons are made of spit.) These cocoons produce the gold standard of textile silk because each one unreels into a single strand of silk. Longer fibers make superior fabric. Most silk comes from the larvae of cocoon-forming insects. However, other insects and, most notably, arachnids also produce silk fiber.

It’s more accurate to define silk as fibers composed predominately of fibroin, an insoluble protein, with sericin, a water-soluble, glue-like protein, coating the filaments. This definition includes all types of naturally-produced and manmade silk. Researchers typically separate the fibroin from the sericin and use the fibroin in their experiments.

Biomedical applications of silk

I got the idea for this blog when I read about Tufts University’s silk portfolio. Two researchers, biomedical engineer David Kaplan and physicist Fiorenzo Omenetto, have developed products ranging from edible optical sensors to multiple biomedical devices. Several qualities of silk – biocompatibility, manipulability, biodegradability, and sustainability – make it highly attractive to biomedical researchers. Silk is also “tunable;” researchers can fashion it into different forms for different purposes. Following are some products, from Tufts, MIT, and elsewhere, that showcase both silk’s qualities and the researchers’ out-of-the-box thinking.

The first silk-based biomedical product from Tufts is a long-term bioresorbable surgical mesh designed for the support and repair of weakened or damaged connective tissue. Pharmaceutical company Allergan bought Serica, the Tufts spinoff that developed this product, in 2010; Allergan continues to develop its potential.

Kaplan and the Tufts team combined fibroin with glycerol to create a self-curing 2D and 3D printer “ink” that can print body tissues and body parts. Previous attempts used thermoplastics and other materials that require heat curing, a process that damages some components. Fabricators can include antibiotics or other compounds with the silk-based ink.

Amanda Brooks, a North Dakota State University researcher, is developing spider silk hydrogels to deliver antibiotics directly to an infection. She tunes the tiny silk bubbles to recognize infection and act only on the infection, not on healthy tissues.

Omenetto’s lab – the Silk Lab at Tufts – and John Rogers of the University of Illinois at Urbana Champaign are exploiting silk’s compatibility with electronics to develop a wireless, remote-controlled, silk-based device referred to as a “magnesium heater,” and designed to kill a localized bacterial infection. When the heater has finished its work, it dissolves harmlessly in the patient.

Image from Tufts University

A brand-new non-medical oddball use for silk

Tufts silk specialists just published news of a method for keeping fruit fresh for at least a week without refrigeration, a technique that could significantly reduce waste incurred when transporting food to market. Fruit coated in a tasteless, odorless, nearly invisible coating of silk exploits silk’s biocompatibility and dissolvability in the human body.

… and an off-the-wall, way out-of-the-box use

MIT researchers led by Markus Buehler have discovered that the different levels of silk’s structure, specifically spider silk, correspond with “the hierarchical elements that make up a musical composition—individual notes assembled into measures, which in turn form a melody, and so on.”

Working with composer John McDonald, a professor of music at Tufts, and MIT postdoc David Spivak, a mathematician who specializes in category theory, Buehler discovered that “strong but useless” protein molecules produced aggressive music, and useful fibers produced softer music. “This taught us that it’s not sufficient to consider the properties of the protein molecules [when designing a molecule] alone,” Buehler says. It’s also necessary to “think about how they can combine to form a well-connected network at a larger scale.”

A wonder material?

Tufts’ Omenetto believes that, while silk might be a wonder material, science should take a broader view. One of the reasons he and others like working with silk is the low impact silk processing and use has on biological systems and the environment. He’d like to see science seek other substances that share this combination of function and low impact. In the meantime, he and other researchers continue to exploit silk’s advantages.

References

https://en.wikipedia.org/wiki/Silk

https://live-sciencefriday.pantheonsite.io/videos/the-medical-wonders-of-worm-spit-2/

https://spectrum.ieee.org/tech-talk/biomedical/devices/silkbased-implants-fight-bacterial-infection-then-vanish-

Image credit:

Wikipedia

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Re: Silk’s Not Just for Neckties

06/13/2016 6:42 PM

Good stuff....It's hard to beat silk fabric for light weight and strength....The biomedical uses are something new I have not heard of before, sounds promising....

https://en.wikipedia.org/wiki/Silk

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Re: Silk’s Not Just for Neckties

06/14/2016 7:40 AM

The development of the 3D printer "ink" strikes me as especially promising. Since the body doesn't react to silk, and silk is already approved for medical use, printed silk "parts" shouldn't have as arduous a journey through the FDA approval process. A group from Tufts and Harvard Medical School are using silk-based plates and screws to hold fractured bone in place (http://hms.harvard.edu/news/translational-research/bone-repair-silk-3-11-14). The potential for custom-designing plates and screws is exciting.

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Re: Silk’s Not Just for Neckties

06/13/2016 10:27 PM

Hmm. Maybe I should have told my wife 16 years ago: "Stick with me kid, and you'll be bleeding into silk". It would have made a better impression than what I told her. But she married me anyway!

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