Figure 2.

Schematic diagram and representative experimental results of (a) molding strategy (adapted with permission from Wang et al. ⁴¹ ), (b) sacrificial material strategy (adapted with permission from Wu et al. ⁴⁶ ), (c) coaxial extrusion strategy (adapted with permission from Zeng et al. ⁵² ), (d) inkjet printing strategy (adapted with permission from Christensen et al. ⁵⁹ ), and (e) lithography-based printing strategy (adapted with permission from Melchiorri et al. ⁶⁰ ).