Biomedical engineers at Tufts University (Medford, MA) have demonstrated the first all-polymeric bone scaffold repair material that is fully biodegradable and can provide significant mechanical support. Employing micron-sized silk fibers to reinforce a silk matrix, the new technology could possibly improve how bones and other tissues are repaired following accidents or diseases.

As reported in the Proceedings of the National Academy of Sciences Online Early Edition, the Tufts researchers were able to develop a fully biodegradable composite with high-compressive strength and improved cell responses related to bone formation in vitro by bonding silk protein microfibers to a silk protein scaffold. They discovered that silk microfiber-protein composite matrices mimicked the mechanical features of native bone, including the matrix stiffness and surface roughness that enhanced human mesenchymal stem cell differentiation. In combination with the inherent strength of silk fiber, compact fiber reinforcement enhanced compressive properties within the scaffolds.

“By adding the microfibers to the silk scaffolds, we get stronger mechanical properties as well as better bone formation," explains David Kaplan, chair of biomedical engineering at Tufts University. "Both structure and function are improved. This approach could be used for many other tissue systems where control of mechanical properties is useful and has broad applications for regenerative medicine.”

To create the scaffolds, the scientists applied alkaline hydrolysis to break down complex molecules into their building blocks. By using this approach, the researchers reduced the time and cost of making the microfibers in a variety of sizes. For example, microfibers ranging in size from 10 to 20 µm were produced in one minute, while conventional processing could produce fibers measuring 100 µm or larger only after 12 minutes.

Despite their achievement, the scientists could produce silk composite scaffolds with significantly lower compressive properties than that of native bone. However, they suggest that such scaffolds can play a valuable role as temporary biodegradable support for native cells to grow.