Degradation of the meniscus—the shock-absorbing knee cartilage that cushions the shinbone from the thighbone—can lead to pain, swelling, stiffness, arthritis and knee replacement surgery. A hydrogel-based material developed at Duke University could one day improve surgical outcomes by enabling replacement knee parts that are custom-shaped to each patient’s anatomy to be 3-D printed.

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

Available implants either do not match the strength and elasticity of the original cartilage, or are not biocompatible and fail to support cell growth that promotes healing around the site. Hydrogels, however, are biocompatible and share a very similar molecular structure to cartilage.

The researchers mixed together two different types of hydrogels—one stiffer and stronger, and the other softer and stretchier—to create a double-network hydrogel. The strength and elasticity of the mixture are adjusted by changing the relative amounts of the two ingredients to achieve a formula that best matches that of human cartilage.

Including nanoparticle clay renders the mock-cartilage 3-D-printable. With this addition, the hydrogel flows like water when placed under shear stress, such as when being squeezed through a small needle. In the absence of stress, the hydrogel immediately hardens into its printed shape.

A synthetic meniscus was 3-D-printed from an X-ray computed tomography image of an anatomical model to demonstrate the potential to customize hydrogel implants based on 3-D images of a patient’s anatomy. The whole process, from scan to finished meniscus, took only about a day.