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Porous membranes are ubiquitous in cell co-culture and tissue-on-a-chip studies. These materials are predominantly chosen for their semi-permeable and size exclusion properties to restrict or permit transmigration and cell-cell communication. However, previous studies have shown pore size, spacing and orientation affect cell behavior including extracellular matrix production and migration. The mechanism behind this behavior is not fully understood. In this study, we fabricated micropatterned non-fouling polyethylene glycol (PEG) islands to mimic pore openings in order to decouple the effect of surface discontinuity from potential grip on the vertical contact area provided by pore wall edges. Similar to previous findings on porous membranes, we found that the PEG islands hindered fibronectin fibrillogenesis with cells on patterned substrates producing shorter fibrils. Additionally, cell migration speed over micropatterned PEG islands was greater than unpatterned controls, suggesting that disruption of cell-substrate interactions by PEG islands promoted a more dynamic and migratory behavior, similarly to enhanced cell migration on microporous membranes. Preferred cellular directionality during migration was nearly indistinguishable between substrates with identically patterned PEG islands and previously reported behavior over micropores of the same geometry, further confirming disruption of cellsubstrate interactions as a common mechanism behind the cellular responses on these substrates. Interestingly, compared to respective controls, there were differences in cell spreading and a lower increase in migration speed over PEG islands compared prior results on micropores with identical feature size and spacing. This suggests that membrane pores not only disrupt cell-substrate interactions, but also provide additional physical factors that affect cellular response.

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Porous membranes are fundamental elements for tissue‐chip barrier and co‐culture models. However, the exaggerated thickness of commonly available membranes may represent a stumbling block impeding a more accurate in vitro modeling. Existing techniques to fabricate membranes such as solvent cast, spin‐coating, sputtering, and plasma‐enhanced chemical vapor deposition (PE‐CVD) result in uniform thickness films. Here, a robust method to generate ultrathin porous parylene C (UPP) membranes is developed not just with precise thicknesses down to 300 nm, but with variable gradients in thicknesses, while at the same time having porosities up to 25%. Surface etching and increased roughness which lead to improved cell attachment is also shown. Next, the mechanical properties of UPP membranes with varying porosity and thickness is examined and the data is fitted to previously published models, which can help determine the practical upper limits of porosity and lower limits of thickness. Lastly, a straightforward approach allowing the successful integration of the UPP membranes into a prototyped 3D‐printed scaffold is validated, demonstrating mechanical robustness and allowing cell adhesion under varying flow conditions. Collectively, the results support the integration and the use of UPP membranes to examine cell–cell interaction in vitro.

Inflammatory diseases and cancer metastases lack concrete pharmaceuticals for their effective treatment despite great strides in advancing our understanding of disease progression. One feature of these disease pathogeneses that remains to be fully explored, both biologically and pharmaceutically, is the passage of cancer and immune cells from the blood to the underlying tissue in the process of extravasation. Regardless of migratory cell type, all steps in extravasation involve molecular interactions that serve as a rich landscape of targets for pharmaceutical inhibition or promotion. Transendothelial migration (TEM), or the migration of the cell through the vascular endothelium, is a particularly promising area of interest as it constitutes the final and most involved step in the extravasation cascade. While in vivo models of cancer metastasis and inflammatory diseases have contributed to our current understanding of TEM, the knowledge surrounding this phenomenon would be significantly lacking without the use of in vitro platforms. In addition to the ease of use, low cost, and high controllability, in vitro platforms permit the use of human cell lines to represent certain features of disease pathology better, as seen in the clinic. These benefits over traditional pre-clinical models for efficacy and toxicity testing are especially important in the modern pursuit of novel drug candidates. Here, we review the cellular and molecular events involved in leukocyte and cancer cell extravasation, with a keen focus on TEM, as discovered by seminal and progressive in vitro platforms. In vitro studies of TEM, specifically, showcase the great experimental progress at the lab bench and highlight the historical success of in vitro platforms for biological discovery. This success shows the potential for applying these platforms for pharmaceutical compound screening. In addition to immune and cancer cell TEM, we discuss the promise of hepatocyte transplantation, a process in which systemically delivered hepatocytes must transmigrate across the liver sinusoidal endothelium to successfully engraft and restore liver function. Lastly, we concisely summarize the evolving field of porous membranes for the study of TEM.

Cellular processes are linked to the alignment (anisotropy) and orientation (directionality) of collagen fibers (i.e., landscape) in the native extracellular matrix (ECM). Given the vital role that cell‐matrix interactions play in regulating biological functions, several microfluidic methods have successfully established anisotropic 3D collagen gels to develop quantitative relationships between structural cues and cellular responses. However, independently tailoring the fiber anisotropy and fiber directionality within a landscape remains a challenge. Here, a user‐friendly microfluidic platform with a non‐uniform channel geometry is used to control the degree of fiber anisotropy and directionality as a function of extensional strain rate and a defined flow path, respectively. New experimental capabilities, including independent control over the degree of fiber anisotropy and directionality, spatial gradients in anisotropy, and multi‐material interfaces, are demonstrated. A channel peel‐off technique provides direct access to the microengineered collagen landscapes, and the alignment of single MD‐MB‐231 cancer cells and monolayers of human umbilical vein endothelial cells (HUVEC) is shown. Finally, the platform's modular capability is highlighted by integrating an ultrathin porous Parylene (UPP) membrane onto the microengineered collagen landscape as a method to control the degree of cell‐matrix interaction.

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Bone tissue engineering is a new and applicable emerging approach to repair the bone defects. Electrical conductive scaffolds through a physiologically relevant physical signaling, electrical stimulation, has shown a highly promise in this approach. In this paper, we fabricated carbon nanofiber/gold nanoparticle (CNF/GNP) conductive scaffolds using two distinct methods; blending electrospinning in which GNP were blended with electrospinning solution, and electrospinning/electrospraying in which GNP was electrosprayed simultaneously with electrospinning. The obtained electrospun mats underwent stabilization/carbonization process.The scaffolds were characterized by SEM, XRD, FT-IR and Raman spectroscopy. SEM characterizations showed improved morphology and a slight decrease in the diameter of the spinned and sprayed nanofibers (from 178.66 ± 38.40 nm to 157.94 ± 24.14 nm and 120.81 ± 13.77 nm, respectively), while XRD analysis confirmed the crystal structure of the nanofibers.Raman spectroscopy revealed enhancement in the graphitization of the structure, and the electrical conductivity of the structure improved by up to 29.2% and 81% in electrospraying and blending electrospinning modes, respectively. Indirect MTT and LDH toxicity assays directly were performed to assess MG63 cell toxicity, but no significant toxicity was observed and the scaffolds did not adversely affect cell proliferation. It can be concluded this structure have potential for bone tissue engineering applications.