Hydrogels are often used as scaffolds in tissue engineering. Living cells introduced into the material can theoretically grow through the gel until a whole piece of tissue is formed. However, to grow well, the cells must interact with each other. Unfortunately, conventional hydrogel scaffolds do not allow for much cell-cell interaction. Granular hydrogels could solve this problem.
Instead of a uniform hydrogel, granular hydrogels are made up of many micrometer-sized subunits that are simply packed together, said Jason Burdick, a bioengineer at the University of Colorado Boulder. As part of a presentation he gave Wednesday to the American Chemical Society’s Division of Polymer Materials: Science and Engineering at the ACS Fall 2024 Meeting, Burdick discussed the work of graduate student Nikolas Di Caprio, who is using the unique properties of granular hydrogels to bioengineer cartilage tissue.
The trick, Burdick told C&EN, is to mix clusters of cells into the granular hydrogel to create a composite material (Adv. Mater. 2024, DOI: 10.1002/adma.202312226). This allows the cells to interact with each other while providing them with the structural stability of the hydrogel.
The space between the subunits of the material allows the gel to flow, making it injectable, but it also creates voids for the cartilage cell clusters to expand into. “The reason we end up getting such good cartilage, I think, is because we’re just creating cellular environments that the cells really like,” Burdick said.
Of course, the material can’t flow indefinitely. After it’s injected into a joint or mold, Burdick said, “we want to sort of click these particles together to stabilize them in that structure.” That’s accomplished by shining a light on the granular gel for 3 minutes. The tiny hydrogel spheres are made of norbornene-modified hyaluronic acid, and under the light, the norbornene groups crosslink to neighboring hydrogel spheres via a dithiol crosslinker.
The work presented “combines two areas where Jason has really pioneered, namely cartilage tissue engineering and microgels,” said Kent Leach, a biomedical engineer at the University of California, Davis. “I think it’s elegant.”
