Fig. 3

a Schematic diagram of the control of hydrogel stiffness by manipulating the crosslinking density using DNA crosslinkers. Reproduced with permission from [56], copyright John Wiley and Sons, 2021. b Schematic and optical images of nitro-dopamine-modified MNP incorporated into a collagen-based hydrogel, and SEM image of its internal microstructure. Reproduced with permission from [67], copyright American Chemical Society, 2016. c Schematic and optical images of an rGO-based hydrogel nanocomposite and its application for the growth and differentiation of myoblasts. Reproduced with permission from [69], copyright Elsevier, 2016