Human Knee

Researchers at University of California have created and are testing artificial tissue, which appears to be up to six times as strong as natural cartilage. They’ve successfully tested it in mice, rabbits, miniature pigs, and sheep, and the next steps are to test it for longer periods of time, and then, ultimately, to test it in humans.

“We’ve made great strides in engineering replacement cartilage. Our work showed, for the first time, that we can create a scaffold-free tissue with properties approaching those of native tissue,” says Jeni Lee, an associate at Novo Ventures, a Ph.D. in biomedical engineering, and an author of a recent study in Nature Materials.

“This achievement gives us comfort that, if implanted, this tissue can withstand load-bearing within the joint and, ultimately, restore joint function,” Lee says. “Ideally, a tissue-engineered cartilage implant would delay the need for a total joint replacement.”

[Read joint replacement news.]

One of the strengths of the new creation, which was constructed in the lab of Kyriacos Athanasiou, who recently moved from UC Davis to UC Irvine, is its “scaffold”-free approach. Scaffolding in bioengineering refers not to something that parallels the kind of temporary apparatus that construction workers use to access out-of-reach parts of a building, but instead to a structure’s supporting walls and beams, according to Lee.

“We can choose to remodel those walls — like creating a bigger dining room — or leave them in place and just live around them. But we cannot easily change some of them, such as major support beams,” she explains. “Similarly in tissue engineering, the cells may remodel the scaffold they are placed in, but they aren’t able to remodel certain scaffolds.”

Researchers have long sought to create artificial cartilage, because the real thing doesn’t regenerate. (The researchers note in the study that as early as the fourth century B.C., Aristotle noted that cartilage “when once cut off [does not] grow again.”)

[Read about knee injections and cartilage growth.]

Lee and her colleagues’ unusual scaffold-free approach, she says, is like a foundation, four walls, and a house roof with no interior walls.

“The cells can then go in and build whatever they want that is best suited for them,” she says. “In reality, the foundation, four walls, and roof do not exist for these cells either.”

“The artificial cartilage that we engineer is fully biological with a structure akin to real cartilage,” explains Athanasiou, on the UC Davis site. “Most importantly, we believe that we have solved the complex problem of making tissues in the laboratory that are strong and stiff enough to take the extremely high loads encountered in joints such as the knee and hip.”

[Read about minding the (joint) gap.]

Three of the biggest challenges inserting the lab-grown cartilage in animals — and eventually into humans — going forward, according to Lee, are integrating the native and engineered cartilage, immobilizing and rehabilitating the patient to allow for healing, and making the implant sufficiently structurally stable that it can bear the joint’s rigorous mechanics.

But the team is optimistic, as Athanasiou told Capital Public Radio. “With our approach, we should be able to treat [cartilage] defects before they destroy the entire joint,” he told the Sacramento station.