FIG. 5.

(a) Printed brain-like layered structures. [a (i)] Illustration of the proposed brain-like layer structure. [(a) (ii)]–[(a) (vii)] The printing process to create a brain-like structure. Each color represents a layer. [(a) (vi)] Confocal microscope images of neurons in different layers after 5 days of culture. The image is colored for the distribution of the cells through the z-axis in the bioink RGD-GG gel as indicated. [(a) (vii)] The expanded view of the area from the square, showing an axon penetrating into the adjacent layer. Scale bars represent 100 mm. Reproduced with permission from Lozano et al., Biomaterials 67, 264–273 (2015). Copyright 2015 Elsevier.¹⁶⁶ (b) 3D bioprinted iPSC-derived neuronal and glial progenitor cells after in vitro culture. [(b) (ii)–(b) (iv)] The image of 3D printed sNPCs and OPCs in a channel after 7 days of culture showing axon projections in close proximity to the OPCs. OPCs express mCherry (red), sNPCs differentiate into neurons and express the β3III-tubulin (green), and the merged image is shown along with a close-up. [(b) (vi)] Distribution of cell types in specific channels: sNPCs only (left), OPCs only (middle), and sNPCs and OPCs (right). sNPCs are detected with human-specific antibody SC121 (red), and OPCs express eGFP (green). The image was taken 24 h post printing. [(b) (vii)] sNPCs and OPCs co-printed in a scaffold after 4 days of culture. β3III-tubulin shows axonal projections down the channels, and the OPCs express mCherry. Reproduced with permission from Joung et al., Adv. Funct. Mater. 28, 1801850 (2018). Copyright 2018 John Wiley & Sons.¹⁶⁷