One Step Closer to Artificial Cartilage

Researchers keep inching toward the goal of creating a synthetic articular cartilage—that all important tissue that cushions the end of bones where they meet at joints. Now Farshid Guilak, M.D., a professor of orthopedic surgery at Duke University and Kuanhe Zhao, Ph.D., assistant professor of mechanical engineering at the same institution, have created artificial replacement tissue that mimics both the strength and suppleness of natural cartilage.

As reported in Science 2.0, in 2007 Guilak and his team developed a three-dimensional fabric “scaffold” into which stem cells could be injected and “grown” into articular cartilage tissue. He constructed the seven layer scaffold from minuscule woven fibers, each layer about as thick as a human hair. The finished scaffold is about 1 millimeter thick.

The next challenge for Guilak was to develop the right medium to fill the empty spaces of the scaffold—a medium that could sustain compressive loads, provide a lubricating surface and support the growth of stem cells. That proved to be difficult. Materials that were supple enough to simulate native cartilage he found to be too fragile to grow in a joint and withstand loading. Stronger substances were not smooth and flexible enough.

Enter Zhao. In 2012 he had 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 in the mid-December 2013 press release. “It has all the mechanical properties of native cartilage and can withstand wear and tear without fracturing.”

Zhao and Guilak began working together to integrate Zhao’s hydrogel into the fabric of Guilak’s 3-D woven scaffolds in a process Zhao compares to pouring concrete over a steel framework. The tests showed that Zhao’s invention was tougher than the materials Guilak had created and had a lower coefficient of friction. The material did not yet meet the standards of natural cartilage but it did outperform 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, founder of Duke’s Soft Active Materials (SAMs) Laboratory. He believes that it is a promising candidate for artificial cartilage in the future.