Researchers at Duke University created a hydrogel-based material that mimics cartilage and it may one day be used to 3-D print knee replacement parts customized for each patient.

In many cases of a torn or damaged meniscus, surgeons have to either partially or completely remove it. The current available implants aren't as strong and elastic as natural cartilage.

"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," Benjamin Wiley, an associate professor of chemistry at Duke, said in a statement.
Hydrogels have a very similar molecular structure to cartilage and they support the growth of cells to encourage healing around the site. But historically it has been a challenge to create recipes for hydrogels that have the same strength as human cartilage and are 3-D printable.

The researchers decided to experiment by combining a stiffer, stronger hydrogel with a softer, more flexible hydrogel to create a double-network hydrogel. They adjusted the amounts of the two hydrogels to achieve a formula that best matches human cartilage.

An ingredient called nano particle clay was also added to make it 3-D-printable. The team then took a CT scan of a plastic model of a knee and used the information to 3-D print new menisci using the double-network hydrogel.

The entire process from the time of the CT scan to the finished 3-D printed menisci took only about a day. In addition, the 3-D printer that was used cost $300.

Customized 3-D-printed implants are already being used for hip replacement, cranial plates and spinal vertebrae procedures.

In February, researchers at Mayo Clinic developed a 3-D printed bioabsorbable scaffold that can reconstruct ruptured anterior cruciate ligaments in the knee and deliver a protein that promotes bone regeneration.

"This is really a young field, just starting out," said Wiley. "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."

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