Disrupted Surfaces of Porous Membranes Reduce Nuclear YAP Localization and Enhance Adipogenesis through Morphological Changes.

The disrupted surface of porous membranes, commonly used in tissue-chip and cellular coculture systems, is known to weaken cell-substrate interactions. Here, we investigated whether disrupted surfaces of membranes with micron and submicron scale pores affect yes-associated protein (YAP) localization and differentiation of adipose-derived stem cells. We found that these substrates reduce YAP nuclear localization through decreased cell spreading, consistent with reduced cell-substrate interactions, and in turn enhance adipogenesis while decreasing osteogenesis.

Porous Substrates Promote Endothelial Migration at the Expense of Fibronectin Fibrillogenesis.

Porous substrates have gained increased usage in cell studies and tissue mimetic applications because they can partition distinct cell types while still allowing important biochemical crosstalk. In the presented work, we investigated how porous substrates with micron and submicron features influence early cell migration and the associated ECM establishment, which can critically affect the rate of cell coverage on the substrate and the ensuing tissue organization. We showed through time-lapse microscopy that cell speed and migratory distance on membranes with 0.5 µm pores were nearly two-fold of those observed on nonporous membranes, while values on membranes with 3.0 µm pores fell in between. Although the cell directionality ratio and the persistence time was unaffected by the presence of pores, the cells did exhibit directionality preferences based on the hexagonal pore patterning. Fibronectin fibrillogenesis exhibited a distinct inverse relationship to cell speed, as the fibrils formed on the nonporous control were significantly longer than those on both types of porous substrates. We further confirmed on a per cell basis that there is a negative correlation between fibronectin fibril length and cell speed. The observed trade-off between early cell coverage and ECM establishment thus warrants consideration in the selection or the engineering of the ideal porous substrate for tissue mimetic applications and may help guide future cell studies.

Membrane Pore Spacing Can Modulate Endothelial Cell-Substrate and Cell-Cell Interactions.

Mechanical cues and substrate interaction affect the manner in which cells adhere, spread, migrate and form tissues. With increased interest in tissue-on-a-chip and co-culture systems utilizing porous membranes, it is important to understand the role of disrupted surfaces on cellular behavior. Using a transparent glass membrane with defined pore geometries, we investigated endothelial fibronectin fibrillogenesis and formation of focal adhesions as well as development of intercellular junctions. Cells formed fewer focal adhesions and had shorter fibronectin fibrils on porous membranes compared to non-porous controls, which was similar to cell behavior on continuous soft substrates with Young's moduli seven orders of magnitude lower than glass. Additionally, porous membranes promoted enhanced cell-cell interactions as evidenced by earlier formation of tight junctions. These findings suggest that porous membranes with discontinuous surfaces promote reduced cell-matrix interactions similarly to soft substrates and may enhance tissue and barrier formation.