Scientists have long studied silk for its strength. Now they're using it to shore up bone. A team of bioengineers from Mexico, India and the U.S. created a silk protein-based scaffolding to encourage new bone cell growth in broken or fractured bones. The new scaffolding is stronger than other manmade bone scaffolds under study, the researchers found. They've just started testing the new material by implanting mice with the scaffolding for four weeks. The Proceedings of the National Academy of Sciences of the United States of America published their work online today (April 30).
Currently, people who need bone scaffolding usually get it from a piece of bone transplanted from healthy bone somewhere else in their bodies, which means they undergo two surgeries – one to harvest healthy bone and one to insert the bone tissue where it's needed. They may also get transplants from donors or use man-made materials. Those options eliminate the harvesting surgery, but they don't work as well as people's own bone tissue, according to the North American Spine Society.
So several research groups are on the lookout for better replacements, and are examining everything from the connective tissue found in mammals, to the hard material in lobster shells, to silk harvested from the same silkworm species that weave fibers for clothes. These biological materials are supposed to work better with the human body than entirely artificial materials.
The group publishing today is headed by a Tufts University researcher, David Kaplan, who studies silk. Kaplan's team created tiny silk fibers, 10 nanometers to 500 nanometers in length, to reinforce a spongy scaffold also made from silk protein. The researchers found that their silk-reinforced silk scaffolds can withstand greater pressure than other biologically-based bone scaffolds. The method they created to make the microfibers is faster and cheaper than the usual technique, they wrote in their paper. The scaffolds also had a rough surface, which encourages bone cell growth.
To check how the implant would fare in an animal, the researchers implanted their bone scaffolding in mice. They found that after one week, the mice's immune cells surrounded the implants, forming a "minimal" immune reaction, according to the paper. After four weeks, they found bone-like cells growing densely around the implants.
The research is a step toward better engineering of bone, the researchers wrote.
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