Fig. 5

3D bioprinted in vitro models of human tissues and organs. a 3D cell-printed skin model composed of epidermis, dermis, hypodermis, and vascular channel. Stained images using representative markers of each layer: b epidermis, c dermis, d vascular channel, and e hypodermis (scale bars, 50 µm). Reproduced with permission from Kim et al.¹¹⁹ f 3D bioprinting of transparent corneal tissue via the alignment of collagen fibers within the nozzle during bioink extrusion. g Second-harmonic generation (SHG) images of shear-aligned collagen using each nozzle. (scale bar, 20 μm). h Distributions of collagen orientations at different azimuthal angles. Reproduced with permission from Kim et al.¹²⁰ i Schematic diagram of the spinal cord illustrating gray matter and white matter boundaries and the 3D bioprinting process. Reproduced with permission from Joung et al.¹²⁴ j Coaxial printing of monolayer and bilayer structures in complex hollow tubes. The schematic represents monolayer (I), bilayer (II), and fine-tuning between monolayer to bilayer at defined intervals in the complex hollow (III) tubes for renal tubular tissue. k A convoluted hollow tube with a transitional region between monolayer and bilayer structures. (scale bars, 1 mm). l Schematic representation of the glomerulus and proximal tubule in native kidney tissue. m 3D bioprinting of complex renal tubular structures. (scale bar, 500 μm). Reproduced with permission from Singh et al.¹³²