When cartilage in joints such as the knees gets damaged, it is very slow to heal – if it ever does at all. An experimental new biohybrid material could one day replace it, however, and may even promote the growth of new natural cartilage.
One of the challenges in designing artificial cartilage lies in the fact that like its natural counterpart, the material must be malleable enough to bend with the joint, yet also tough enough to withstand the loads constantly placed upon it.
In the past, substances made of natural polymers such as collagen, fibrin or hyaluronic acid have been put forth as replacement materials, as have purely synthetic substances. According to scientists at Cornell University, neither approach has successfully combined the two key qualities of real cartilage.
With that limitation in mind, the researchers developed a biohybrid material consisting of natural collagen fibers suspended within a synthetic hydrogel. The gel is zwitterionic, meaning that each ion within it is both positively and negatively charged.
When the hydrogel and collagen are initially mixed, the ions in the gel interact with the positively and negatively charged ions in the collagen fibers, causing the latter to self-assemble into an interconnected network like that in natural collagen. The resulting material is thus tough and resilient, yet also soft and flexible.
In lab tests, the biohybrid was found to "approach the performance" of natural joint cartilage – it was 40 percent more elastic than zwitterionic gel without the added collagen, plus it possessed 11 times the fracture energy (which is a measure of durability). Additionally, because the new material is biocompatible, it can play host to adjacent cartilage cells which migrate into it and reproduce.
"Ultimately, we want to create something for regenerative medicine purposes, such as a piece of scaffold that can withstand some initial loads until the tissue fully regenerates," said Asst. Prof. Nikolaos Bouklas, who is leading the study along with Prof. Lawrence Bonassar. "With this material, you could 3D print a porous scaffold with cells that could eventually create the actual tissue around the scaffold."
The research is described in a paper that was recently published in the journal Proceedings of the National Academy of Sciences.
Source: Cornell University
