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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.

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.