Biomedicine: The silk road to recovery

Thanks to some remarkable properties, silk is finding its way inside the body.

Chinese Princess Xi Ling Shi usually gets credit for the discovery of silk as a usable fibre in 2640 BC. Legend has it that she was the first to unravel a silkworm’s cocoon after it fell in her teacup. There’s no way she could have known then that those cocoons would not only be farmed to spin into cloth, but also to make a stronger breast implant and internal body sensors.

But that’s exactly what’s happening in the biomedical and technological research and development right now. It turns out that silk’s combination of superior strength, like Kevlar, and flexibility, like nylon, makes it incredibly versatile. Plus, the silkworm is a renewable resource, and perhaps most important, the absence of toxic chemicals in the silk proteins means the body can often absorb the silk.

Much of the research on the applications of silk come out of the Tufts School of Engineering at Tufts University in Medford, Mass., in particular from the work of two biomedical engineering researchers, Fiorenzo Omenetto and David Kaplan. “I was intrigued by the remarkable mechanical properties of these fibres spun by worms and spiders,” Kaplan says of what made him investigate silk in 1989. Omenetto began to study silk just five years ago, intrigued by the material’s remarkable optical properties.

Together, the two worked alongside John Rogers, a researcher at the University of Illinois, on an optics project that explores the potential of “silicon-on-silk” electronics. But these devices aren’t for computers or cellphones, they’re actually meant to go inside the body, and could one day monitor the body’s functions (say, blood sugar levels for a diabetic). The silk allows the device to integrate with the human body, and after some time, slowly dissolve into the surrounding tissue.

But there are still a number of obstacles to full commercial production. “Achieving biocompatibility can be challenging,” said Rogers when the research was published in the journal Applied Physics Letters. “Electronic devices made to be implanted in the body are usually encased to protect them. [In our approach] a major portion of the electronics is simply consumed by the body, as their function in monitoring or healing is no longer needed.”

While that research continues, there’s healing potential locked in the very same fibres that scientists have begun to tap.

In early 2009, a Massachusetts-based biomaterials provider called Serica Technologies (which is affiliated with Tufts through its CEO, Greg Altman), successfully won FDA approval for its SeriScaffold product. The product is a surgical mesh made out of a fibre protein from the silkworm. The scaffold is also bio-resorbable like the sensors, which means they can be absorbed by the body without requiring mechanical removal.

The original press release sold SeriScaffold as the answer for the sophisticated tissue-repair needs of the estimated 60,000 women who annually undergo breast reconstruction procedures as a result of illnesses such as breast cancer. It explained that the silk product could be absorbed more slowly than other proteins like collagen, which would “enable optimal healing” by providing a better, longer-lasting support system for tissue or implants.

At the beginning of 2010, Serica Technologies was acquired by Allergan, a health-care company that focuses on developing innovative pharmaceuticals, but also makes Botox and Natrelle breast implants. Now that Serica is a wholly owned subsidiary, it’s unclear how Allergan plans to develop these products. Along with the SeriScaffold, Serica also brought other silk innovations to Allergan, including SeriGel (a silk product used in plastic surgery and drug delivery), and SeriACL graft (a biodegradable ligament graft that is used for ligament repair).

To fill the need for silk in the future, scientists are capable of making the proteins in a lab, but sometimes mother nature does it best. “It is only if you are making very high-strength materials that you need to revert to the native fibres,” says Kaplan, although he says it’s easier to purify and process the man-made stuff. Still, Omenetto and Kaplan say there may one day be the potential to grow silk like cotton, so it can be harvested. For now, the most common medical application for silk is medical tape and silk suture sets, mostly made in the same country whose princess introduced the world to silk thousands of years ago.