Mending menisci with 3D printed hydrogel

The hydrogel-based material is claimed to be the first to match human cartilage in strength and elasticity while also remaining 3D-printable and stable inside the body. To demonstrate how it might work, the researchers used a $300 3D printer to create custom menisci for a plastic model of a knee.

"We've made it very easy now for anyone to print something that is pretty close in its mechanical properties to cartilage, in a relatively simple and inexpensive process," said Benjamin Wiley, an associate professor of chemistry at Duke and author on the paper - 3D Printing of a Double Network Hydrogel with a Compression Strength and Elastic Modulus Greater than that of Cartilage - which appears online in ACS Biomaterials Science and Engineering.

Surgeons can attempt to repair a torn or damaged meniscus, but often it must be partially or completely removed. Available implants either do not match the strength and elasticity of the original cartilage, or are not biocompatible.

Hydrogels have been gaining traction as a replacement for lost cartilage as they are biocompatible and share a very similar molecular structure to cartilage. Researchers have, however, struggled to create recipes for synthetic hydrogels that are equal in strength to human cartilage or that are 3D-printable.

"The current gels that are available are really not as strong as human tissues, and generally, when they come out of a printer nozzle they don't stay put - they will run all over the place, because they are mostly water," Wiley said.

Feichen Yang, a graduate student in Wiley's lab and author on the paper, experimented with mixing together two different types of hydrogels - one stiffer and stronger, and the other softer and stretchier - to create a double-network hydrogel.

"The two networks are woven into each other," Yang said. "And that makes the whole material extremely strong."

By changing the relative amounts of the two hydrogels, Yang could adjust the strength and elasticity of the mixture to arrive at a formula that best matches that of human cartilage.

He also mixed in a nanoparticle clay to make the mock-cartilage 3D-printable. With the addition of the clay, the hydrogel flows like water when placed under shear stress, such as when being squeezed through a small needle. But as soon as the stress is gone, the hydrogel hardens into its printed shape.

In a simple demonstration, Yang took a CT scan of a plastic model of a knee and used the information from the scan to 3D print new menisci using his double network hydrogel. The whole process, from scan to finished meniscus, took only about a day, he said.