Gradient chondroitin sulfate/poly (γ-glutamic acid) hydrogels inducing differentiation of stem cells for cartilage tissue engineering

Based on the gradient distribution of structure and composition in biological cartilage tissue, we designed a gradient hydrogel scaffold by the moving photomask, using chondroitin sulfate and poly (γ-glutamic acid) as crude materials. The hydrogel scaffold had a gradient distribution of cross-linking density, which can be verified from the results of SEM and swelling behavior. Besides, the hydrogel exhibited great viscoelastic, toughness (70% strain), and strength properties (600 kPa). Additionally, the gradient hydrogel's superior cell compatibility was proved through the MTT, live/dead staining assays, and 3D cell culture experiments. Remarkably, the results of in vitro stem cell differentiation experiments showed that the duration of light directly affected the differentiation extent of stem cells, demonstrating that the gradient hydrogel scaffold can better simulate the function of natural cartilage than the homogeneous one. Due to these outstanding characteristics, this gradient hydrogel is a potential scaffold for cartilage tissue engineering. Graphical abstract • We use chondroitin sulfate/poly (γ-glutamic acid) as raw materials to prepare hydrogels to simulate natural cartilage ECM. • We introduce photomask technology to control the gradient crosslinking density of the hydrogel scaffold, which has a mild reaction. • The hydrogel has a complete continuous gradient structure similar to natural cartilage, and there is no interface combination problem. • The hydrogel has anisotropic pore morphology, swelling and biological properties to mimic natural cartilage. • The stem cell differentiation can be induced by gradient differences in mechanical properties without growth factors