Fig. 4

Single-step fabrication of soft layered gels. a Horizontal layers (in different colors) are created from an agarose solution in a single-step process by injecting 100 ml 4 wt% agarose solution with 0.0015 wt% methylene blue hydrate into 100 ml 9.1 wt% NaCl solution containing 0.002 wt% fluorescein sodium salt. Boundaries of the layers are marked with dashed lines. The layers differ from one another in softness due to the different concentrations of agarose, i.e. the bottom layers are softer than those at the top. b–d Cylindrical gel slabs, which are cut from different layers in the gel, show different mechanical properties. Therefore, applying the same vertical load on the slabs results in different degrees of compression and thus indicates the different Young’s moduli of the gel in these horizontal layers