Kevlar-based artificial cartilage mimics the magic of the real thing

Kevlar-based artificial cartilage mimics the magic of the real thing
The artificial cartilage is very flexible yet resistant to tearing. Credit: Joseph Xu, Michigan Engineering Communications & Marketing

The unparalleled liquid strength of cartilage, which is about 80 percent water, withstands some of the toughest forces on our bodies.

Synthetic materials couldn't match it—until "Kevlartilage" was developed by researchers at the University of Michigan and Jiangnan University.

"We know that we consist mostly of —all life does—and yet our bodies have a lot of structural stability," said Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering at U-M, who led the study. "Understanding cartilage is understanding how life .forms can combine properties that are sometimes unthinkable together."

Many people with joint injuries would benefit from a good replacement for cartilage, such as the 850,000 patients in the U.S. who undergo surgeries removing or replacing cartilage in the knee.

While other varieties of synthetic cartilage are already undergoing clinical trials, these materials fall into two camps that choose between cartilage attributes, unable to achieve that unlikely combination of strength and water content.

The other that mimic the physical properties of cartilage don't contain enough water to transport the nutrients that cells need to thrive, Kotov said.

Kevlar-based artificial cartilage mimics the magic of the real thing
Cells survive well in the synthetic cartilage matrix: green cells are alive, and red cells are dead. Credit: Lizhi Xu, Kotov Lab, University of Michigan.

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.

The 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.

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 stand up to 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.

Kevlar-based artificial cartilage mimics the magic of the real thing
An electron microscope image of the synthetic cartilage matrix. Credit: Lizhi Xu, Kotov Lab, University of Michigan.

As 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 . 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."

Kotov is a member of the Biointerfaces Institute, which provides shared space for researchers from U-M's engineering and medical schools. He is also a professor of chemical engineering, science and engineering, and macromolecular science and engineering.

The study, recently published in Advanced Materials, is titled "Water-rich biomimetic composites with abiotic self-organizing nanofiber network." It was supported by the National Science Foundation, with additional funding from the Department of Defense. The university is seeking patent protection and partners to bring the technology to market.


Explore further

Artificial cartilage under tension as strong as natural material

More information: Lizhi Xu et al. Water-Rich Biomimetic Composites with Abiotic Self-Organizing Nanofiber Network, Advanced Materials (2017). DOI: 10.1002/adma.201703343
Journal information: Advanced Materials

Citation: Kevlar-based artificial cartilage mimics the magic of the real thing (2017, November 15) retrieved 24 August 2019 from https://phys.org/news/2017-11-kevlar-based-artificial-cartilage-mimics-magic.html
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User comments

Nov 15, 2017
A better "mesh" for hernia repair?

Nov 16, 2017
A better "mesh" for hernia repair?

Possibly.
AND, it'd be bulletproof...:-)

Nov 16, 2017
A better "mesh" for hernia repair?

I was thinking exactly the same thing. This would work much better than the titanium replacements currently used for herniated lumbar discs.

Dec 06, 2017
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 stand up to 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.


What an astounding DESIGN!

There's definite PURPOSE and great execution resulting from intimate knowledge, understanding and ABILITY to create the requisite structures. Plus - it's totally bio-compatible with it's surroundings. It remains to be seen whether the artificial cartilage will not induce some kind of reaction.

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