Currently, metal fixation systems are the gold standard for fracture fixation, and fixation devices are usually made of metal alloys. But metal devices can have disadvantages: they can cause stress on the underlying bone because they are stiffer and less bendable. They can also cause an increased risk of infection and poor wound healing. In some cases, metal implants must be removed after the fracture heals, forcing a second surgery. Recently, resorbable fixation devices, composed of synthetic polymers, have attracted the attention of many scientists because they lack stress masking and so can avoid removal and can improve bone reconstruction. However, their use is limited to pediatric craniofacial procedures, which may pose a risk of inflammatory reactions and are difficult to implant. Currently, a team of researchers from Tufts University School of Engineering and Israel Medical Center (BIDMC) have developed surgical plates and screws using silk proteins from cocoons that not only improve bone reconstruction after injury, but more importantly, can also be absorbed by the body over time, eliminating the need for surgical removal of the device. This device is no less efficacious than the currently used polylactic acid glycolic acid fixation system. Related findings were published in the March 4, 2014, issue of Nature Communications. Dr. Samuel Lin, co-author of the paper and associate professor of surgery at Harvard Medical School, noted, “Unlike metals, the composition of silk proteins may be more similar to that of bone components. The silk protein material is very strong. They maintain structural stability under very high temperatures and other harsh conditions, and they can be easily sterilized.” According to co-senior author David Kaplan, chair of Tufts University’s Department of Biomedical Engineering, “Another great advantage of silk proteins is that they can stabilize and deliver biologically active components, so plates and screws made of silk proteins could actually deliver antibodies to prevent infection, deliver drugs to enhance bone regeneration and provide other therapies to support recovery. “ Previously, Kaplan and his research group have developed silk-based sponges, fibers and foams for use in surgical suites and clinical settings. But until now, silk proteins have not been used to develop a solid medical device for fracture fixation. The researchers used silk proteins obtained from the cocoons of the domestic silkworm (Bombyx mori) to prepare surgical plates and screws. Silk proteins are produced in the glands of the domestic silkworm and fold in a complex manner, resulting in unique properties: exceptional strength and versatility. To test the new device, the researchers took a total of 28 silk-made screws and implanted them into six laboratory rats. The screws were inserted very directly and then tested at four and eight weeks after implantation. Kaplan noted that all screws were successfully implanted during the implantation process. Because silk swells very slowly, the new devices maintained their mechanical integrity even when they encountered fluid and surrounding tissue during the procedure. The results show that the use of silk plates and screws allows patients to avoid the complications associated with metal or synthetic polymer devices when they come into contact with fluid. Lin said, “The resorbable, long-lasting plate and screw system has tremendous application potential.” Although originally intended to treat facial trauma with filament screws (occurring at a rate of hundreds of thousands per year), the device still has the potential to treat a variety of different fracture types. Lin adds that because silk screws are inherently ray-permeable, they may make it easier for surgeons to see the progress of a fracture after surgery without the obstruction of a metal device. Once the fracture has healed, these screws and plates will disappear, which has significant benefits. Researchers will continue this study in larger animal models and eventually for clinical trials in humans.