Cartilage-like hydrogel promises 3D-printable knee implants

Far more than a simple hinge, the human knee is a complex, intricate mechanism, and a knee injury is a painful and debilitating of condition that's difficult and expensive to repair. Duke University is developing a cartilage-like material based on hydrogel that may make the task of repairing knees easier. 

The 3D-printable hydrogel allows bioengineers to create bespoke artificial replacement parts for injured knees that are tailored to match the old part both in shape and mechanical properties.

The current hydrogels lack the strength and ooze away when put through a 3D printer due to their high water content, so the Duke researchers are looking at a new hydrogel-based material that they claim is the first to match human cartilage in strength and elasticity, yet is 3D-printable. It was created by Yang, who combined a stiff strong hydrogel with one that is soft and stretchy. When mixed, the polymer chains wove together to create a new hydrogel that is strong and elastic. More importantly, by altering the proportions, these properties could be controlled across different parts of the artificial meniscus.

Yang then added a nanoparticle clay to the hydrogel to make it printable. When subjected to shear stress, the clay particles collapse into a smooth-flowing liquid, but once in place after oozing through a printing needle, they set hard to hold up the hydrogel structure.

Using a US$300 printer, Yang was able to print a replacement meniscus with the new hydrogel in only a day – showing that what was once a daunting manufacturing process could soon be simple and inexpensive.