In this paper, we report a new method to incorporate 3D scaffold with electrotaxis measurement in the microfluidic device. The electrotactic response of lung cancer cells in the 3D foam scaffolds which resemble the in vivo pulmonary alveoli may give more insight on cellular behaviors in vivo. The 3D scaffold consists of ordered arrays of uniform spherical pores in gelatin. We found that cell morphology in the 3D scaffold was different from that in 2D substrate. Next, we applied a direct current electric field (EF) of 338 mV/mm through the scaffold for the study of cells’ migration within. We measured the migration directedness and speed of different lung cancer cell lines, CL1-0, CL1-5, and A549, and compared with those examined in 2D gelatin-coated and bare substrates. The migration direction is the same for all conditions but there are clear differences in cell morphology, directedness, and migration speed under EF. Our results demonstrate cell migration under EF is different in 2D and 3D environments and possibly due to different cell morphology and/or substrate stiffness.

We describe a recently developed oblique-incidence reflectivity difference (OI-RD) microscope, a form of polarization-modulated imaging ellipsometer, for label-free–high-throughput detection of biomolecular reactions on DNA and protein microarrays. We present examples of application of this technique to end-point and real-time investigations of DNA–DNA hybridization, antibody–antigen capture, and protein–small-molecule binding reactions. Compared to a conventional imaging ellipsometer based on the polarizer–compensator–sample–analyzer scheme and under the off-null condition, a polarization-modulated OI-RD microscope is inherently more sensitive by at least 1 order of magnitude to thickness changes on a solid surface. Compared with imaging surface plasmon resonance microscopes based on reflectance change on falling or rising slopes of the surface plasmon resonance, the OI-RD microscope (1) has a comparable sensitivity, (2) is applicable to conventional microscope glass slides, and (3) easily covers a field of view as large as the entire surface of a $1\text{\hspace{0.17em} in .}\times 3\text{\hspace{0.17em} in .}$ $(2.54\mathrm{c}\mathrm{m}\times 7.62\mathrm{c}\mathrm{m})$ microscope slide.

The wound-healing assay is an easy and economical way to quantify cell migration under diverse stimuli. Traditional assays such as scratch assays and barrier assays are widely and commonly used, but neither of them can represent the complicated condition when a wound occurs. It has been suggested that wound-healing is related to electric fields, which were found to regulate wound re-epithelialization. As a wound occurs, the disruption of epithelial barrier short-circuits the trans-epithelial potential and then a lateral endogenous electric field is created. This field has been proved invitro as an important cue for guiding the migration of fibroblasts, macrophages, and keratinocytes, a phenomenon termed electrotaxis or galvanotaxis. In this paper, we report a microfluidic electrical-stimulated wound-healing chip (ESWHC) integrating electric field with a modified barrier assay. This chip was used to study the migration of fibroblasts under different conditions such as serum, electric field, and wound-healing-promoting drugs. We successfully demonstrate the feasibility of ESWHC to effectively and quantitatively study cell migration during wound-healing process, and therefore this chip could be useful in drug discovery and drug safety tests.

Interactions of glycan-binding proteins (GBPs) with glycans are essential in cell adhesion, bacterial/viral infection, and cellular signaling pathways. Experimental characterization of these interactions based on glycan microarrays typically involves (1) labeling GBPs directly with fluorescent reagents before incubation with the microarrays, or (2) labeling GBPs with biotin before the incubation and detecting the captured GBPs after the incubation using fluorescently labeled streptavidin, or (3) detecting the captured GBPs after the incubation using fluorescently labeled antibodies raised against the GBPs. The fluorescent signal is mostly measured ex situ after excess fluorescent materials are washed off. In this study, by using a label-free optical scanner for glycan microarray detection, we measured binding curves of 7 plant lectins to 24 glycans: four β1-4-linked galactosides, three β1-3-linked galactosides, one β-linked galactoside, one α-linked N-acetylgalactosaminide, eight α2-3-linked sialosides, and seven α2-6-linked sialosides. From association and dissociation constants deduced by global-fitting the binding curves, we found that (1) labeling lectins directly with fluorescent agents change binding profiles of lectins, in some cases by orders of magnitude; (2) those lectin–glycan binding reactions characterized with large dissociation rates, though biologically relevant, are easily missed or deemed insignificant in ex situ fluorescence-based assays as most captured lectins are washed off before detection. This study highlights the importance of label-free real-time detection of protein–ligand interactions and the potential pitfall in interpreting fluorescence-based assays for characterization of protein–glycan interactions.

A key step leading to influenza viral infection is the highly specific binding of a viral spike protein, hemagglutinin (HA), with an extracellular glycan receptor of a host cell. Detailed and timely characterization of virus-receptor binding profiles may be used to evaluate and track the pandemic potential of an influenza virus strain. We demonstrate a label-free glycan microarray assay platform for acquiring influenza virus binding profiles against a wide variety of glycan receptors. By immobilizing biotinylated receptors on a streptavidin-functionalized solid surface, we measured binding curves of five influenza A virus strains with 24 glycans of diverse structures and used the apparent equilibrium dissociation constants (avidity constants, 10–100 pM) as characterizing parameters of viral receptor profiles. Furthermore by measuring binding kinetic constants of solution-phase glycans to immobilized viruses, we confirmed that the glycan-HA affinity constant is in the range of 10 mM and the reaction is enthalpy-driven.

Collective cell migration plays important roles in various physiological processes. To investigate this collective cellular movement, various wound-healing assays have been developed. In these assays, a “wound” is created mechanically, chemically, optically, or electrically out of a cellular monolayer. Most of these assays are subject to drawbacks of run-to-run variations in wound size/shape and damages to cells/substrate. Moreover, in all these assays, cells are cultured in open, static (non-circulating) environments. In this study, we reported a microfluidics-based wound-healing assay by using the trypsin flow-focusing technique. Fibroblasts were first cultured inside this chip to a cellular monolayer. Then three parallel fluidic flows (containing normal medium and trypsin solution) were introduced into the channels, and cells exposed to protease trypsin were enzymatically detached from the surface. Wounds of three different widths were generated, and subsequent wound-healing processes were observed. This assay is capable of creating three or more wounds of different widths for investigating the effects of various physical and chemical stimuli on wound-healing speeds. The effects of shear stresses, wound widths, and β-lapachone (a wound healing-promoting chemical) on wound-healing speeds were studied. It was found that the wound-healing speed (total area healed per unit time) increased with increasing shear stress and wound width, but under a shear stress of 0.174 mPa the linear healing speed (percent area healed per unit time) was independent of the wound width. Also, the addition of β-lapachone up to 0.5 μM did not accelerate wound healing. This microfluidics-based assay can definitely help in understanding the mechanisms of the wound-healing process and developing new wound-healing therapies.