A new way to make artificial cartilage uses 3D woven fibers and hydrogel to mimic the strength and suppleness of the real stuff.
Articular cartilage is the tissue on the ends of bones where they meet at joints in the body 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 Farshid Guilak, a professor of orthopedic surgery and biomedical engineering at Duke University, and his team developed a 3D fabric “scaffold” into which stem cells could be injected and successfully “grown” into articular cartilage tissue. Constructed of minuscule woven fibers, each of the scaffold’s seven layers is about as thick as a human hair. The finished product is about one 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.
Xuanhe Zhao, assistant professor of mechanical engineering and materials science, 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. “It has all the mechanical properties of native cartilage and can withstand wear and tear without fracturing.”
He and Guilak began working together to integrate the hydrogel into the fabric of the 3D 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 Zhao’s invention 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 use of hydrogel and scaffolding on their own. The research appears in the journal Advanced Functional Materials.
“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. “It’s a very promising candidate for artificial cartilage in the future.”
The team’s next step will likely be to implant small patches of the synthetic cartilage in animal models, according to Guilak and Zhao.
The National Institutes of Health, the Arthritis Foundation, the Collaborative Research Center, AO Foundation, Davos, Switzerland and the NSF helped support the project.
Source: Duke University