Published in the journal of Advanced Functional Materials Volume 23, Issue 47, page 5825, December 17, 2013
A Duke research team has developed a better recipe for synthetic replacement cartilage in joints.
Tiny interwoven fibers make up the three-dimensional fabric “scaffold” into which a strong, pliable hydrogel is integrated and injected with stem cells, forming a framework for growing cartilage. This image appears on the cover of the Advanced Functional Materials Dec. 17, 2013. Credit: courtesy of Frank Moutos and Farshid Guilak
Combining two innovative technologies they each helped develop, Farshid Guilak, a professor of orthopedic surgery and biomedical engineering, found a way to create artificial replacement tissue that mimics both the strength and suppleness of native cartilage. The results of this work appear Dec. 17 in the journal Advanced Functional Materials.
Articular cartilage is the tissue on the ends of bones where they meet at joints in the body â€“ including in the knees, shoulders and hips. It can erode over time or be damaged by injury or overuse, causing pain and lack of mobility. While replacing the tissue could bring relief to millions, replicating the properties of native cartilage — which is strong and load-bearing, yet smooth and cushiony — has proven a challenge.
In 2007 Guilak and his team developed a three-dimensional fabric “scaffold” into which stem cells could be injected and successfully “grown” into articular cartilage tissue. Constructed of minuscule woven fibers. The finished product is about 1 millimeter thick.
Since then, the challenge has been 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. Materials supple enough to simulate native cartilage have been too squishy and fragile to grow in a joint and withstand loading. “Think Jell-O,” says Guilak. Stronger substances, on the other hand, haven’t been smooth and flexible enough.
To address this issue, Guilak started working with Xuanhe Zhao, assistant professor of mechanical engineering and materials science. Zhao proposed a theory for the design of durable hydrogels (water-based polymer gels) and in 2012 collaborated with a team from Harvard University to develop an exceptionally strong yet pliable interpenetrating-network hydrogel.
“It’s extremely tough, flexible and formable, yet highly lubricating,” Zhao says.
He and Guilak began working together 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 their experiments, the researchers compared the resulting composite material to other combinations of Guilak’s scaffolding embedded with previously studied hydrogels. The tests showed that the composite material was tougher than the competition with a lower coefficient of friction. And though the resulting material did not quite meet the standards of natural cartilage, it easily outperformed all other known potential artificial replacements across the board, including the hydrogel and scaffolding by themselves.
The team’s next step will likely be to implant small patches of the synthetic cartilage in animal models, according to Guilak.
Their work was supported in part by National Institutes of Health grants AG15768, AR50245, AR48182, AR48852, the Arthritis Foundation, the Collaborative Research Center, AO Foundation, Davos, Switzerland and the NSF (CMMI-1253495, CMMI-1200515, and DMR-1121107).