An inverted dielectrophoretic device for analysis of attached single cell mechanics

Abstract

Dielectrophoresis (DEP), the force induced on a polarizable body by a non-uniform electric field, has been widely used to manipulate single cells in suspension and analyze their stiffness. However, most cell types do not naturally exist in suspension but instead require attachment to the tissue extracellular matrix in vivo. Cells alter their cytoskeletal structure when they attach to a substrate, which impacts cell stiffness. It is therefore critical to be able to measure mechanical properties of cells attached to a substrate. We present a novel inverted quadrupole dielectrophoretic device capable of measuring changes in the mechanics of single cells attached to a micropatterned polyacrylamide gel. The device is positioned over a cell of defined size, a directed DEP pushing force is applied, and cell centroid displacement is dynamically measured by optical microscopy. Using this device, single endothelial cells showed greater centroid displacement in response to applied DEP pushing force following actin cytoskeleton disruption by cytochalasin D. In addition, transformed mammary epithelial cell (MCF10A-NeuT) showed greater centroid displacement in response to applied DEP pushing force compared to untransformed cells (MCF10A). DEP device measurements were confirmed by showing that the cells with greater centroid displacement also had a lower elastic modulus by atomic force microscopy. The current study demonstrates that an inverted DEP device can determine changes in single attached cell mechanics on varied substrates.

Characterization of biomechanical properties of cells through dielectrophoresis-based cell stretching and actin cytoskeleton modeling

“…The R 2 value obtained from the two curves were >0.98, indicating good fit for the data. Similar to the findings reported in [22, 47], the DEP method was found to yield a higher force value as compared to other characterization methods such as AFM.…”

“…They concluded that bead attachment could strongly affect the force applied to the cells, and increased stress in magnetic cytometry could reinforce nonlinearity and cellular plasticity. Urbano et al [22] examined attached epithelial cells by using DEP pushing and AFM indentation method and found that the elastic modulus differed by at least 10 times. Fortier et al [50] used AFM to characterize leukemia cells with two different probes and they found that the elastic moduli evaluated from a conical probe were larger, and their distribution was wider, as compared to the results from a spherical probe.…”

“…These two methods, however, suffer from low throughput and lengthy system setup. Dielectrophoresis (DEP) has increasingly received attention in recent years because it can be used as a simple alternative to other conventional approaches in characterizing the mechanical properties of a cell [18–22]. DEP-based cell electro-deformation was first reported in 1984 [23], and this technique involves the basic working principle of polarizing and stretching cells by using a non-uniform electric field produced by a pair of electrodes.…”

Cell properties assessment using optimized dielectrophoresis-based cell stretching and lumped mechanical modeling

“…An optimum electrode configuration is the one that is less detrimental to the cells and provides the largest elongation under similar conditions (applied voltage and frequency) for the same cell and medium. We studied six configurations based on different configurations studied in other literature 22 – 26 , including rectangular, elliptical, triangular, and combinations, depicted in Fig. 4 b.…”

“…At low frequencies (lower than 100 kHz) direct contact between electrodes and the fluid leads to bubbles. In previous studies 25 , 26 , hydrogenated silicon nitride has been used as a passivation layer to avoid the formation of bubbles. Here, we used diluted SU8 (MicroChem) by cyclopentanone as a passivation layer (Fig.…”