Spiders and Worms: The All-Organic Way to Mend Bones
WHY YOU SHOULD CARE
Because if you break a bone, wouldn’t you rather hold it together with something that dissolves when everything’s healed?
By Kenneth Skinner
Kanye West’s music video for his breakout single “Through the Wire” may have made rapping with a reconstructed jaw look easy. In reality, the medical implants used to mend fractured bones can result in a number of complications. But soon, we may be able to kiss those clunky plates and screws goodbye — thanks to a wriggling caterpillar roughly the size of a pinkie finger.
Many medical devices are made of metal alloys, an extremely stiff material that often must be surgically removed after healing and can even corrode in the body, causing pain and swelling. But what if implants could work more seamlessly — and organically — within our bodies? Imagine a silk screw in your fractured bone that simply dissolves after doing its job.
Unlike metal, silk protein composition more closely resembles our own bones.
Scientists are looking to the humble silkworm in the quest for more natural, pliable alternatives. The silkworm’s salivary glands spew one of the world’s strongest, most durable fibers. Don’t be fooled by its diaphanous appearance — weight for weight, it’s as strong as steel when stretched. In a recent Nature Communications paper, investigators tested the use of natural-silk-based screws for use in surgery.
Silk is a global, multibillion-dollar trade, and its products have broad use, from operating rooms to wedding dresses. Biotech firms are searching for ways to commercialize silk-derived products on a grand scale, which could very well lead to the beginnings of a new biotech Silk Road.
Why silk? Silk, which has been FDA-approved for use in medical devices, has building blocks naturally present in the body. Which means that, unlike metal, silk protein composition more closely resembles our own bones.
Silk-based materials have been studied for their utility in humans in other ways, such as antibiotic injections. Antibiotics can be loaded into silk and then released in the body’s deep tissues, where traditional injections couldn’t penetrate an infection site. Silk materials are also very robust and stay stable at very high temperatures —170 degrees Celsius, or 338 degrees Fahrenheit — which also helps keep the antibiotics sterile.
The Nature Communications study found that the silk screws remained in the bone for up to eight weeks before gradually being reabsorbed by the body, eliminating the need for surgical removal. And since silk is invisible on X-ray radiographs, the screws don’t obstruct doctors’ views of the healing process around the wound.
Spider silk has been tested as a coating material for silicone breast implants.
For many years, silkworm-derived silk has been used for bandages and textiles, but don’t discount silk from other, less cuddly bugs — like spiders. Spider silk is very elastic (it can even be used for violin strings), conducts heat as well as metals and, by weight, is tougher than silkworm silk and steel. But spider silk has seen very little commercialization — most likely because spiders may spend more time cannibalizing each other than spinning silk.
So a synthetic option would be more commercially viable. Enter AMSilk, a finalist in last year’s Ernst & Young’s Entrepreneur of the Year competition. The German firm has developed the first and only biotech production method for making man-made silk biopolymers. How exactly?
AMSilk relies on genetically modified E. coli bacterium (one that won’t land you in the hospital). Spider silk genes are inserted into bacteria, which essentially programs the bacteria to make spider silk protein. AMSilk uses this process to make silk powder for shampoos and cosmetics. In shampoo, the spider silk is supposed to adhere to keratin, the key structural protein in hair, and make damaged hair look and feel, well, silkier.
Spider silk has also been tested for a more unlikely cosmetic application: silicone breast implants. AMSilk has completed preclinical testing for BioShield-S1, an ultrathin coating of spider silk proteins that modifies the implant’s surface during the first months after implantation — when a patient’s immune system is most sensitive to the foreign material. The findings, published this year in Advanced Functional Materials, showed that the silk coating shields the implants from immune attack, which often triggers scarring, swelling and other side effects.
Other companies are also hopping aboard the spider silk bandwagon.
For instance, Spiber uses bacteria to produce spidroin, a main structural protein in spider silk. One gram of the protein (named Qmonos, from kumo-no-su, the Japanese phrase for “spiderweb”) produces about 5.6 miles of artificial silk — enough to make hundreds of silk screws that can be used for bone fractures. Currently, the Swedish startup can produce 1 kilogram of the silk protein per day and is developing facilities to produce on a much larger scale.
Then there’s Randy Lewis, a biology professor at Utah State University, who has scaled his silk production using genetically modified goats that produce spider silk protein in their milk. A new 70,000-square-foot facility at the university will house large fermentation equipment to process the goats’ milk and maximize synthetic spider silk production. Lewis founded Araknitek in 2012 to commercialize applications for spider silk such as tire threads and even material for 3-D printing.
Instead of chasing silkworms and spiders, companies are now looking to other organisms, such as bacteria, that they hope will yield vast amounts of modified silk protein and help them build an even larger web of commercial applications and medical breakthroughs. Take that, Spider-Man.
Kenneth Skinner is a Morehouse graduate and a Ph.D. candidate in chemical biology at Harvard University.
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