Once it's been injured, the protective cartilage in our knees and other joints heals very slowly – if at all. A new injectable gel, however, could both reinforce the tissue after it's been damaged, and encourage new cartilage to grow over top of it.
Currently being developed by scientists at the University of Pennsylvania, the hydrogel contains a modified form of a gooey substance known as hyaluronic acid, which is produced naturally by the body's connective tissue. In recent years, the acid has also been experimentally used to ward off glaucoma, heal damaged cardiac tissue, and refill herniated spinal discs.
In lab tests, the U Pennsylvania hydrogel was injected into degenerated joint cartilage in mice. Such cartilage covers the interfacing ends of the bones within a joint, and when not damaged, it keeps them from painfully grinding against one another as that joint moves.
It was found that after being injected, the hydrogel intertwined with the structural matrix of the cartilage, thus stabilizing and strengthening it. This finding was backed up by other tests, in which the gel restored the regular activity of cartilage-producing/maintaining chondrocyte cells in living cartilage tissue samples.
Additionally, the sticky hyaluronic acid hydrogel was found to provide a good "roosting" surface for mesenchymal stem cells that were subsequently injected into the injured joint. Those cells proceeded to grow into a new external layer of cartilage, further protecting the recently reinforced original tissue beneath.
"We often relate this combined approach to treating a damaged deck in your backyard," says the lead scientist, Asst. Prof. Jay Patel. "To fortify the existing wood structure, you need something like a wood hardener, then you can apply a wood sealer to prevent future wear. In the same way, we applied a substance that seeps into the pores of the tissue and provides reinforcement, then 'sealed' it by guiding the behavior of injected stem cells towards forming a layer that caps the whole structure."
Studies on larger animals are now being planned, followed by clinical trials on humans.
The hydrogel is currently being commercialized by spinoff company Forsagen, and is described in a paper that was recently published in the journal Advanced Healthcare Materials. Scientists at the University of Delaware are also developing an injectable hyaluronic acid-based hydrogel, which in their case releases pain-killing medication into joints as they're moving.
Source: University of Pennsylvania
