Nano- and Micro-Patterned S-, H-, and X-PDMS for Cell-Based Applications: Comparison of Wettability, Roughness, and Cell-Derived Parameters

Structure and dynamics of ESCRT-III membrane remodeling proteins by high-speed atomic force microscopy

Endosomal Sorting Complex Required for Transport (ESCRT) proteins assemble on the cytoplasmic leaflet of membranes and remodel them. ESCRT is involved in biological processes where membranes are bent away from the cytosol, constricted, and finally severed, such as in multi-vesicular body formation (in the endosomal pathway for protein sorting) or abscission during cell division. The ESCRT system is hijacked by enveloped viruses to allow buds of nascent virions to be constricted, severed and released. ESCRT-III proteins, the most downstream components of the ESCRT system, are monomeric and cytosolic in their autoinhibited conformation. They share a common architecture, a four-helix bundle with a fifth helix that interacts with this bundle to prevent polymerizing. Upon binding to negatively charged membranes, the ESCRT-III components adopt an activated state that allows them to polymerize into filaments and spirals, and to interact with the AAA-ATPase Vps4 for polymer remodeling. ESCRT-III has been studied with electron microscopy (EM) and fluorescence microscopy (FM); these methods provided invaluable information about ESCRT assembly structures or their dynamics, respectively, but neither approach provides detailed insights into both aspects simultaneously. High-speed atomic force microscopy (HS-AFM) has overcome this shortcoming, providing movies at high spatio-temporal resolution of biomolecular processes, significantly increasing our understanding of ESCRT-III structure and dynamics. Here, we review the contributions of HS-AFM in the analysis of ESCRT-III, focusing on recent developments of non-planar and deformable HS-AFM supports. We divide the HS-AFM observations into four sequential steps in the ESCRT-III lifecycle: 1) polymerization, 2) morphology, 3) dynamics, and 4) depolymerization.

Micropatterning of cells via adjusting surface wettability using plasma treatment and graphene oxide deposition

The wettability of a polymer surface plays a critical role in cell-cell interaction and behavior. The degree to which a surface is hydrophobic or hydrophilic affects the adhesion and behavior of cells. Two distinct techniques for patterning the surface wettability of a Cyclic Olefin Copolymer (COC) substrate were developed and investigated in this article for the purpose of patterning cell growth. These include oxygen plasma treatment and graphene oxide (GO) coating to alter the wettability of the COC substrate and create hydrophilic patterned regions on a hydrophobic surface. When the two techniques are compared, patterning the surface of COC using GO film results in a more stable wettability over time and increases the roughness of the patterned area. Interestingly, both developed techniques were effective at patterning the COC surface’s wettability, which modulated cell adhesion and resulted in micropatterning of cell growth. The novel methods described herein can be used in the fields of cell and tissue culture as well as in the development of new biological assays.

Pervaporation-assisted in situ formation of nanoporous microchannels with various material and structural properties

Nanoporous structures are crucial for developing mixed-scale micro-/nanofluidic devices because they facilitate the manipulation of molecule transport along the microfluidic channel networks. Particularly, self-assembled particles have been used for fabricating various nanoporous membranes. However, previous self-assembly mechanisms relied on the material and structural homogeneities of the nanopores. Here, we present a pervaporation-assisted in situ fabrication method that integrates nanoporous membrane structures into microfluidic devices. The microfluidic devices contain a control-channel layer at the top, which induces local and addressable pervaporation, and the main-channel layer, which is present at the bottom with pre-designated locations for nanoporous microchannels; the layers are separated using a gas-permeable film. The target particle suspensions are loaded into the main channels, and their pervaporation is controlled through the gas-permeable film, which successfully assembles the particles at the pre-designated locations. This method yields nanoporous microchannels with various material and structural properties by fabricating heterogeneous nanopore arrays/junctions in series and other diverse structures along the microchannels. We validate the basic working principle of microfluidic devices containing nanoporous microchannels. Furthermore, we theoretically analyze the fundamental experimental results, which suggest the remarkable potential of our strategy to fabricate nanopore networks without using conventional nanofabrication methods.

Micro-cavities on PDMS microchannel replicated from sandpaper templates trap cells to enhance cell adhesion and proliferation

Polydimethylsiloxane (PDMS) launched its fame in constructing micro-devices for studying cell growth, cell-cell interaction, assembling organ-on-chip models because of its excellency in optical transparency, gas permeability, nontoxicity, elastics, and well-developed...

A rapid nucleic acid concentration measurement system with large field of view for a droplet digital PCR microfluidic chip

Droplet digital polymerase chain reaction (ddPCR) is an effective technique, with unparalleled sensitivity, for the absolute quantification of target nucleic acids. However, current commercial ddPCR devices for detecting the gene chip are time consuming due to complex image stitching. To address this issue, we propose a universal concentration determination system and realize one-time gene chip imaging with high resolution. All the functional units are controlled by self-developed software using the PyQt5 module in Python. Without stitching technology, images of the ddPCR chip (28 mm × 18 mm) containing 20 000 independent 0.81 nL micro chambers can be obtained in less than 15 seconds, which saves about 165 seconds. A white laser light source (2 mW cm^-2) was employed as a substitute for the mercury lamp. Its wavelength matches well with typical fluorescent dyes (e.g., HEX, ROX and Cy5), and thus it can strengthen the fluorescence intensity for weak signals. The results also demonstrated that the correlation coefficient for the measured concentration and theoretical value was above 99%, by testing the ddPCR products with COVID-19 virus. Such a system can greatly reduce the time required for image acquisition and DNA concentration determination, and thus is able to speed up the lab-to-application process for ddPCR technology.

A method for high-content functional imaging of intracellular calcium responses in gelatin-immobilized non-adherent cells

Functional imaging of the intracellular calcium concentration [Ca²⁺]_i using fluorescent indicators is a powerful and frequently applied method for assessing various biological questions in vitro, including ion channel function and intracellular signaling in homeostasis and disease. In functional [Ca²⁺]_i imaging experiments, the fluorescence intensity of single cells is typically recorded during application of a chemical stimulus, i.e. by exchange of modified extracellular media, exposure to drugs and/or ligands. The concomitant mechanical perturbation caused by the perfusion of different solution during experimentation severely hinders calcium imaging in non-adherent cells, including peripheral immune cells, as cells in suspension are dislocated by turbulent flow during chemical stimulation. The quantitative analysis, involving time-courses of intracellular fluorescence signal changes, necessitates cells to remain at the same position throughout the experiment. To prevent dislocation of cells during solution exchange, and to enable imaging as well as analysis of Ca²⁺ responses in immune cells, a gelatin-based method for immobilization of non-adherent cells was developed. Gelatin has been a long-serving material for cell immobilization, e.g. in 3D bio-printing of cells and has thus, also been employed in the context of this study. To demonstrate the applicability of the established method for functional Ca²⁺ imaging in gelatin-immobilized suspension cells, a proof-of-concept study was conducted using human peripheral blood model cell lines (Jurkat/T-lymphocytes and THP-1/monocytes), Ca²⁺ indicators (Fluo-4 and Fura-2) and two different fluorescence microscopy rigs. The data presented that the established methodology is applicable for studying Ca²⁺ signaling by in vitro high-content functional imaging of [Ca²⁺]_i in suspension cells, including but not restricted to human immune cells.