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How Silk Could Drive Ortho Innovation

Medical device experts are getting pretty innovative with orthopedic implant materials, even engineering special titanium dioxide nanotube surfaces. But they might have a bit of competition from Mother Nature.

Surgical plates and screws made from pure silk protein not only offer improved bone remodeling, but also can also be absorbed by the body over time, according to a research team from Tufts University School of Engineering and Beth Israel Deaconess Medical Center.

Tufts Beth Israel Deconess silk screws
Silk-based screws, as shown on Tufts University's website

"One of the other big advantages of silk is that it can stabilize and deliver bioactive components, so that plates and screws made of silk could actually deliver antibiotics to prevent infection, pharmaceuticals to enhance bone regrowth and other therapeutics to support healing," David Kaplan, PhD, co-senior author and Tufts chair of biomedical engineering, said in a news release.

The research on silk-based orthopedic implants was published Tuesday in the journal Nature Communications.

Kaplan and colleagues had already developed silk-based sponges, fibers, and foams for use in the operating room and clinical settings. But using the protein to create an actual implantable, solid medical device for fracture fixation presented new challenges.

The solution came through taking the silk protein obtained from Bombyx mori (B. mori) silkworm cocoons and folding it in  complex ways that give it exceptional properties when it came to strength and versatility.

The next step was to try out 28 silk-based screws in six laboratory rats, with assessments conducted at four and eight weeks after implantation.

"No screws failed during implantation," Kaplan says. Better yet, the silk-based plates and screws appeared to have an advantage over metal or synthetic polymer plates when it comes to interacting with bodily fluid and tissues. Because silk is slow to swell, it maintained mechanical integrity in such situations.

Granted, the screws still need to be tried out in people. But the implications are still exciting.

"Having a resorbable, long-lasting plate and screw system has potentially huge applications," says co-senior author Samuel Lin, MD, of the Division of Plastic and Reconstructive Surgery at Beth Israel Deaconess Medical Center and associate professor of surgery at Harvard Medical School.

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The silk-based screws might initially be used to treat the hundreds of thousands facial injuries that take place annually. But Lin suspects there is potential to treat a variety of bone fractures with them.

"Because the silk screws are inherently radiolucent [not seen on X-ray] it may be easier for the surgeon to see how the fracture is progressing during the post-op period, without the impediment of metal devices," Lin says.

"And having an effective system in which screws and plates 'melt away' once the fracture is healed may be of enormous benefit," Lin says. "We're extremely excited to continue this work in larger animal models and ultimately in human clinical trials."

Silk isn't only naturally derived material that has been getting attention from medical device designers lately.

Last year, a group of U.S., Iraqi, and Spanish research reported that they had demonstrated proof of concept for a heart pulse sensor and current-driven actuator devices based on spider silk coated with functionalized carbon nanotubes.

The researchers--from Florida State University, University of Baghdad (Iraq), Institut de Ciencia de Materials de Barcelona (Spain), and Institucio Catalana de Recerca (Spain)--found the coated fibers are four times tougher than neat silk fiber, versatile and multi-functional, and exhibit polar, shapeable, conducting, flexible, strain- and humidity-sensitive properties, according to their paper in Nature Communications.

Meanwhile, Carnegie Mellon University's Chris Bettinger and Jay Whitacre found that cuttlefish ink provides just the right chemistry and nanostructure to power tiny, ingested electronic devices.

Chris Newmarker is senior editor of MPMN and Qmed. Follow him on Twitter at @newmarker.

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