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. 2022 Mar 14;10:846230. doi: 10.3389/fbioe.2022.846230

FIGURE 6.

FIGURE 6

Strategies for creating gradients that could be implemented in microphysiological systems. (A) Engineered signaling centers for the spatially controlled patterning of human pluripotent stem cells, showing schematic of the microfluidic device a single unit of the device, a picture of the PDMS microfluidic device filled with colored ink in the distinct compartments, and computational simulation of the diffusion of a reference molecule from the source side of the cell chamber after 48 h of perfusion. [Reproduced from (Manfrin et al., 2019) with permission]. (B) Schematic representation of scaffold-mediated spatially graded gene delivery strategy implemented to create a spatial distribution of Runx2 retrovirus within 3D matrices. The proximal portion of collagen scaffolds was coated with PLL before incubation in retroviral supernatant and fibroblast seeding. Representation of a fibroblast-seeded construct containing spatial patterns of noncovalently immobilized retrovirus, showing distribution of Runx2 retrovirus (R2RV) created by partially coating the proximal portion (left side) of collagen scaffolds with PLL at a dipping speed of 170 μm/s before incubation in retroviral supernatant and cell seeding. Confocal microscopy images demonstrating a graded distribution of FITC-labeled PLL (green) (B) and FITC-labeled PLL gradient colocalized with uniformly distributed cell nuclei (DAPI, blue), and immunohistochemical staining for eGFP (pink) counterstained with hematoxylin (blue) revealed elevated eGFP expression on the proximal scaffold portion coated with PLL-R2RV. [Reproduced from (Phillips et al., 2008. Copyright (2008) National Academy of Sciences, United States) with permission]. (C) Nanofiber scaffolds with gradations in mineral content for mimicking the enthesis using a graded coating of calcium phosphate on a nonwoven mat of electrospun nanofibers by submerging in 10× concentrated simulated body fluid added at a constant rate to linearly reduce the deposition time from the bottom to the top end of the substrate (d refers to the distance from the bottom edge of the substrate) (Left). SEM images of graded calcium phosphate coatings on the PLGA nanofibers from different regions, with d = 0 mm representing the longest exposure to SBF and d = 11 mm representing the shortest exposure to SBF [Reproduced from (Li et al., 2009) with permission].