To stimulate the growth of type II collagen -- the main protein in the clean, smooth cartilage that caps bones where they make contact in joints -- the NU researchers created a bioactive nanogel that can be injected into the joint in a minimally invasive manner. The gel self-assmebles into a fibrous, solid extracellular matrix similar to what joint cells see in natural cartilage production. The gel also binds to one of the key growth factors for cartilage regeneration and keeps it localized in the damaged area. This stimulates the stem cells present in bone marrow that in turn activate type II collagen production naturally. The matrix slowly breaks down into nutrients as the natural cartilage builds up, eventually being replaced altogether by locally grown cartilage tissue.