Table 1.

Most common polymers for cartilage hydrogel scaffolds and their biological activities.

Polymer	Properties	References
Collagen	It has chondro-inductive properties which lead to a suitable 3-D microenvironment for enhancing MSC chondrogenesis. Collagen can also provide immunomodulatory properties by reducing certain immunogenic effects.	[28–30]
Chondroitin sulfate	It provides chondro-protective and anti-inflammatory properties to enhance cartilage tissue regeneration. Furthermore, it increased the production of collagen type II.	[23]
Hyaluronic acid (HA)	It improves early-stage chondrogenesis and was proved to repair osteochondral defects in vivo studies. HA interacts with receptors such as CD44 to adjust signal transduction and stem cell differentiation.	[11, 31, 32]
Alginate	It enhances the proliferation of chondrocytes and maintains the chondrocyte phenotype. Its fast and simple gelation makes it suitable for injection.	[33, 34]
Chitosan	The similarity of its structure with GAG leads to chondrocyte proliferation and chondrogenesis. It also improves chondrocyte homeostasis.	[35, 36]