These tiny interwoven fibers make up the 3-D fabric "scaffold" into which a strong, pliable hydrogel is integrated and infiltrated with stem cells, forming a framework for growing cartilage. The resulting composite material is tough, flexible and formable and has excellent frictional properties. It mimics both the strength and suppleness of native cartilage.
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Duke University's Farshid Guilak, a professor of orthopedic surgery and biomedical engineering, and Xuanhe Zhao, assistant professor of mechanical engineering and materials science, combined two technologies they each helped develop to create a better formula for synthetic replacement cartilage in joints.
Guilak and his team had developed a 3-D fabric "scaffold" into which stem cells could be injected and successfully "grown" into articular cartilage tissue. Made of tiny woven fibers, each of the scaffolds seven layers is about as thick as a human hair, with the finished product about 1 millimeter thick. His next step was to develop the right medium to fill the empty spaces of the scaffold, one that can sustain compressive loads, provide a lubricating surface and potentially support the growth of stem cells on the scaffold. Zhao, on the other hand, had proposed a theory for the design of durable hydrogels--water-based polymer gels--and in 2012, he collaborated with a team from Harvard University to develop an exceptionally strong yet pliable interpenetrating-network hydrogel. Zhao and Guilak then worked in partnership to integrate the hydrogel into the fabric of the 3-D woven scaffolds in a process Zhao compares to pouring concrete over a steel framework.
In comparing the resulting composite material to other combinations of Guilak's scaffolding embedded with previously studied hydrogels, the researchers found that Zhaos invention was tougher, and with a lower coefficient of friction. While the resulting material did not quite meet the standards of natural cartilage, it easily outperformed all other known potential artificial replacements, including the hydrogel and scaffolding by themselves. "From a mechanical standpoint, this technology remedies the issues that other types of synthetic cartilage have had," says Zhao. "Its a very promising candidate for artificial cartilage in the future."
The team plans on implanting small patches of the synthetic cartilage in animal models as the next step.
This research was supported in part by the National Science Foundation (grants CMMI 12-53495, CMMI 12-00515 and DMR 11-21107). [Note: This image appeared on the cover of the Dec. 17, 2013, issue of Advanced Functional Materials.]
To learn more about this research, see the Duke news release Duke Engineers Make Strides Toward Artificial Cartilage. (Date of Image: 2012)