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Single-cell mechanics measurements are crucial in understanding mechanotransduction and cellular properties, such as adhesion and stiffness. Here, we present a microfluidic probe device that can generate controlled hydrodynamic loads on single cells in an open cell culture environment. The device is optimized to produce uniform stresses across the area of a cell for cell adhesion measurements. Microfluidic probe (MFP) devices that can be used to create hydrodynamically confined flows (HCMs) have emerged as a unique device for selectively treating cells and surfaces. Typical MFP devices generate complex-shaped flows and non-uniform hydrodynamic loads on the surface beneath the device. We have used computational fluid dynamics to optimize the port geometry of the MFP device to generate an HCM with uniform shear stresses in a region beneath the device. The devices were fabricated from a combination of silicon and PDMS and characterized through flow experiments above a polyacrylamide gel seeded with fluorescent beads. Bead displacements were measured as a function of flow conditions and general agreement with the model was obtained. Finally, we have used the devices to characterize the adhesion strength of patterned fibroblast cells adhered to a collagen-coated substrate. The results presented establish a design for an MFP device that can apply controlled mechanical forces to cells in open liquid environments.

This paper describes both qualitative and quantitative analysis of rapid microvortex flow generation and manipulation induced by opto-electrohydrodynamic technique. A flow named twin opposing microvortex (TOMV) is generated by infrared laser light under non-uniform alternating current (AC) electric fields. For the AC electric fields, frequency ranges from 3 kHz up to 2 MHz while the voltage is changed up to 10 Vp-p (peak-to-peak voltage). Simultaneously, the laser shines either of a pair of electrodes with a power of 0.5 W. Micron-resolution particle image velocimetry technique has been used to construct the velocity fields of the TOMV flow. The strength of the TOMV flow can be tuned by adjusting the AC voltage and frequency. The maximum measurable in-plane velocity of 54.7 µm s−1 outside electrode regions can be achieved with an AC signal of 9 Vp-p and 107 kHz and a laser beam of 0.5 W. This is achieved with indium tin oxide electrodes located on the top surface of a microchamber, in which the electrodes are 16 µm wide and 300 µm long with a spacing of 73 µm between them. This three-dimensional flow generation can be used for in situ micropump and mixing.

The development and analysis of the performance of microfluidic components for lab-on-a-chip devices are becoming increasingly important because microfluidic applications are continuing to expand in the fields of biology, nanotechnology, and manufacturing. Therefore, the characterization of fluid behavior at the scales of micro- and nanometer levels is essential. A variety of microfluidic velocimetry techniques like micron-resolution Particle Image Velocimetry (μPIV), particle-tracking velocimetry (PTV), and others have been developed to characterize such microfluidic systems with spatial resolutions on the order of micrometers or less. This article discusses the fundamentals of established velocimetry techniques as well as the technical applications found in literature.