More than 30 million people in the United States suffer from osteoarthritis (OA), the most common type of arthritis. The damage or breakdown of joint cartilage between bones mostly causes OA, which is sometime called degenerative joint disease or “wear and tear” arthritis.
For years scientists have struggled to develop a material with the unparalleled liquid strength of cartilage, which is about 80 percent water. Synthetic materials couldn't match it—until "Kevlartilage.”
Developed by researchers with the University of Michigan and China’s Jiangnan University, this new Kevlar-based hydrogel recreates the magic of cartilage by combining a network of tough nanofibers from Kevlar—the aramid fibers best known for making bulletproof vests—with a material commonly used in hydrogel cartilage replacements called polyvinyl alcohol, or PVA.
"We know that we consist mostly of water—all life does—and yet our bodies have a lot of structural stability," says Nicholas Kotov, the Michigan-engineering professor who led the study. "Understanding cartilage is to understand how life forms can combine properties that are sometimes unthinkable together."
Synthetic cartilage materials fall into two camps that choose between cartilage attributes, unable to achieve that unlikely combination of strength and water content. Kotov says synthetic materials that mimic the physical properties of cartilage don't contain enough water to transport the nutrients that cells need to thrive.
Meanwhile, hydrogels—which incorporate water into a network of long, flexible molecules—can be designed with enough water to support the growth of the chondrocytes cells that build up natural cartilage. Yet those hydrogels aren't especially strong. They tear under strains a fraction of what cartilage can handle.
In natural cartilage, the network of proteins and other biomolecules gets its strength by resisting the flow of water among its chambers. The pressure from the water reconfigures the network, enabling it to deform without breaking. Water is released in the process, and the network recovers by absorbing water later.
This mechanism enables high impact joints, such as knees, to withstand punishing forces. Running repeatedly pounds the cartilage between the bones, forcing water out and making the cartilage more pliable, as a result. Then, when the runner rests, the cartilage absorbs water so that it provides strong resistance to compression again.
The synthetic cartilage boasts the same mechanism, releasing water under stress and later recovering by absorbing water like a sponge. The aramid nanofibers build the framework of the material, while the PVA traps water inside the network when the material is exposed to stretching or compression. Even versions of the material that were 92 percent water were comparable in strength to cartilage, with the 70-percent version achieving the resilience of rubber.
Because the aramid nanofibers and PVA don't harm adjacent cells, Kotov anticipates that this synthetic cartilage may be a suitable implant for some situations, such as the deeper parts of the knee. He also wonders whether chondrocytes might be able to take up residence inside the synthetic network to produce a hybrid cartilage.
But his potential applications are not limited to cartilage. He suspects that similar networks, with different proportions of aramid nanofibers, PVA and water, may be able to stand in for other soft tissues.
"We have a lot of membranes in the body that require the same properties. I would like to evaluate the space," Kotov said. "I will talk to doctors about where the acute need is and where this intersection of the properties will allow us to make best headway and biggest impact."
Results of the study were published in Advanced Materials.
BCC Research’s new report on hydrogels, Hydrogels: Applications and Global Markets to 2022, observes that hydrogels present excellent opportunities for advancements in wound care, drug delivery and agriculture applications. As demonstrated by “Kevlartilage,” traditional solutions are unable to meet the needs of advanced wound care and controlled release of active ingredients. Super absorbent polymer hydrogels have proven their worth and have reached a stage of dominance in their application areas.
BCC Research estimates the global market for hydrogels to reach $16.5 billion in 2017 and $22.3 billion by 2022, growing at a compound annual growth rate (CAGR) of 6.3%.
To learn more about this vibrant market, download the free report overview.