How scientists are engineering silk to save our bodies

Silk has been valued for millennia, but in recent years, scientists have paid attention to the material because it is extraordinarily strong, so it is useful for bulletproof vests and body armor. The potential of silk is more than just protecting the exterior of our anatomy, however, researchers are now designing silk so that one day it can heal our wounds, hold our bones and become part of our bodies.

Silk is made by silkworms for their cocoons and by spiders for their nets. The two types are spun differently and have some different properties. (For example, silk made by worms tends to be weaker). But in both cases, the material is strong, elastic and safe to use within the human body, which opens it up to a wide range of medical uses.

A silkworm farm in Indonesia.
Photo by Nurcholis Anhari Lubis / Getty Images

One possibility is that silk can heal our wounds faster. In a study recently published in the journal Advanced Science scientists designed silkworms to spin a material activated by the light it disinfects. First, the researchers identified all the natural proteins that could be activated by a specific type of light to create a chemical reaction that kills pathogens, according to Young Kim, a material scientist at Purdue University and co-author of the article.

Next, scientists genetically manipulated silkworms by inserting this protein, called mKate 2, into their DNA. These silkworms then produced a bright red silk activated by visible green light, like a regular LED light. When scientists put something E. coli bacteria in the red silk and flashed a green light on it for an hour, the survival rate of the bacteria was reduced by 45 percent. This process is very similar to the use of hydrogen peroxide to disinfect a cut, says Kim. Fluorescent silk and light together generate chemicals similar to hydrogen peroxide.

Silk does not distinguish harmful pathogens (such as E. coli) from benign ones, but, as Kim points out, neither does hydrogen peroxide. And we still do not know the minimum time that light needs to shine on silk to be effective. But the discovery is exciting and the material could be used in devices that purify air and water and in many areas of health. In another recent work, Kim and his team discovered the exact physical properties that make silk cool, which is useful in treating inflammation. This finding could help us make the silk even colder, or design other fabrics to cool them down too. Between the effects of automatic silk cooling and these antibacterial properties, it could be an ideal material for advanced bandages.

Silk can also be used to prop up parts of our body. When we fracture or break bones, doctors usually implant a piece of metal to stabilize the area until it is fixed. Most of the time, these metals, such as stainless steel and titanium, are very stiff and can cause more fractures, according to Mei Wei, a materials scientist at the University of Connecticut. When the bone heals, the doctors need to do another surgery to remove the metal. Wei and his team created a silk form that could offer a better solution. It is strong but also elastic, and will degrade inside the body after about a year, eliminating the need for another surgery. Their results were published this month in Journal of the Mechanical Behavior of Biomedical Materials.

The team combined a protein found in spider silk, called fibroin, with a plastic form and a type of calcium that is found in our bones. The result is much stronger than natural bone. In fact, it has the highest recorded resistance for a material that can also be absorbed in the body, says Wei. The team is still improving it with the hope that it can improve and be even stronger before testing animals and then in clinical trials, he adds.

The big problem with silk is that it is expensive to manufacture. Silkworms are rare and difficult to breed, and spider farms are generally not an attractive idea. But the material inside the trees, called wood-based nanocellulose, is strong and cheap. A possible solution is to combine the two in a cheap and even better material. Nanocellulose is also durable. After all, "when nature builds a tree, it needs to give it a good mechanical structure and performance so that the tree does not fall," says Daniel Söderberg, researcher at the KTH Royal Institute of Technology in Stockholm and author of the document ACS Nano on this hybrid material. The team of Söderberg put them together: nanocellulose for strength and silk for greater hardness and elasticity. "We are using the basic components of nature and we combine them," he says.

The material is on par with Kevlar, and could be used for bulletproof vests. But one day, it could also be used to replace parts of the body. This material decomposes in the natural world, but not inside our bodies because they can not process the nanocellulose. Still, it's safe and the cells grow in it and around it. And its elasticity makes it ideal for certain parts of the body such as tendons.

Tendons are difficult to replace precisely because of their need to stretch. At this time, there is no easy way to correct them, and replacement often means taking tendons from another part of the body. The silk-nanocellulose hybrid has the necessary properties that could be used to replace a tendon, says Söderberg. However, to get there, he and his team try to further improve the resistance of the material and are also studying the economics of the process, for example, how to produce it easily and economically so that the possibility of silk as a part of the body and all other potentials of a strong silk come to fruition.

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