Apr 20, 2017 | By Tess

A team of researchers from Duke University in North Carolina is developing a novel 3D bioprinting material that could one day be used to create patient-specific cartilage implants. The innovative cartilage-mimicking material is made from a hydrogel mixture and could be used to 3D print menisci implants to repair damaged knees.

To anyone who has suffered a knee injury and has been instructed to wear a knee brace for pretty much the rest of their lives, the news coming out of Duke University will be very exciting. In a paper recently published in the journal ACS Biomaterials Science and Engineering, a team of researchers from Duke University has described its process of developing a hydrogel-based material that can be 3D printed into custom, cartilage-mimicking structures.

While the project is still in its early stages, the researchers did demonstrate how a low-cost $300 3D printer could be used to 3D print the biocompatible material into a meniscus-shaped structure which was then implanted onto 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,” explained Benjamin Wiley, an associate professor of chemistry at Duke University who contributed to the research paper.

Menisci, for those unfamiliar with the human knee’s anatomy, are a pair of cartilage-based “shock absorbers” which are located between the thigh and shin bones. They are essentially responsible for cushioning and protecting our bones with every step, jump, and movement we take. But while our menisci protect our knees, they are not impervious to damage themselves, as even minor knee injuries can damage the cartilage, resulting in pain and potentially causing such conditions as arthritis.

Current treatments for repairing or replacing damaged menisci are limited, however, as existing implants are not as strong as the original cartilage or are not fully biocompatible. The research being done at Duke University is hoping to offer a suitable alternative to these existing treatments, one that provides both biocompatibility and strength.

(Image: WebMD)

Within the biomedical field, the benefits of hydrogels are becoming increasingly apparent, as the biocompatible materials have a similar molecular structure to cartilage. However, a few challenges still exist with the materials. “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,” explained Wiley.

The Duke research project is addressing these challenges and has found an innovative way to overcome them, at least on the 3D printing front. Feichen Yang, one of the team’s researchers has been experimenting with mixing two different types of hydrogels together: one stiff and strong, the other soft and stretchy.

By combining both hydrogels using a “double-network” technique, the team was able to create a material that could be adjusted to have specific properties. Then, by adding a nanoparticle clay to the mixture, Yang was able to make the hydrogel mixture 3D printable. As the researchers explain it, the clay makes the hydrogel mixture turn to liquid when it is under shear stress (like being extruded) but then solidify when the stress is gone.

With their new process, the researchers are hopeful that, one day in the future, 3D printing could be used to create customized shapes out of the cartilage-mimicking material to be implanted in patients. For menisci treatments especially, being able to print bespoke shapes could offer big benefits. As Wiley said: “Shape is a huge deal for the meniscus. This thing is under a lot of pressure, and if it doesn’t fit you perfectly it could potentially slide out, or be debilitating or painful.”

Additionally, being able to adjust the hydrogel’s properties so that they are variable (i.e. softer on one end and stronger in the middle) could allow for the implants to more closely mimic a real meniscus—a feat which is impossible when using more traditional molding techniques.

Despite the technology being in its early stages, the Duke team has already demonstrated its feasibility using a plastic knee model. More specifically, the team 3D scanned a plastic knee model and created a 3D model of the menisci, which were then 3D printed using the double-network hydrogel. The entire process reportedly only took a day, marking what is certainly a promising start.

“This is really a young field, just starting out,” Wiley commented. “I hope that demonstrating the ease with which this can be done will help get a lot of other people interested in making more realistic printable hydrogels with mechanical properties that are even closer to human tissue.”



Posted in 3D Printing Materials



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