Acoustophoresis is rapidly gaining prominence in the field of cell manipulation. In recent years, researchers have extensively used this method for separating different types of cells from the bulk fluid. In this paper, we propose a novel acoustophoresis-based technique to capture infected or abnormal erythrocytes from blood plasma. A typical acoustic device consisting of a transducer assembly, microfluidic cavity, and a reflector is considered. Based on the concept of impedance matching, a pair of antibody-coated polystyrene layers is placed in the nodal regions of an acoustic field within the cavity. This technique allows bi-directional migration of the suspended cells to the biofunctionalized surfaces. Therefore, simultaneous capture of infected erythrocytes on both the layers is feasible. Finite element method is used to model the pressure field as well as the motion of erythrocytes under the influence of acoustic radiation, drag, and gravitational forces. A parametric analysis is done by varying the excitation frequency, driving voltage, and the thickness of the polystyrene layers. The resulting changes in the pressure amplitude and field pattern are investigated. The erythrocyte collection efficiency, rate of collection, and the cell distribution on the layer surfaces are also determined under different field conditions. The occurrence of transient cavitation in the blood plasma-filled cavity at the chosen frequency is taken into account by using its threshold pressure value as the limiting factor of pressure amplitude. The study provides an insight into the phenomenon and serves as a guideline to fabricate low-cost, multifunctional rapid diagnostic devices based on acoustophoretic separation.
biophysical cues. [1,2] Signaling molecules regulate cell migration under normal physiological conditions by controlling cell adhesion and cytoskeleton organization. [1,3,4] Conversely, pathological conditions such as metastatic cancer, vascular disease, and chronic inflammation are associated with unregulated cell migration, contributing to disease progression. [4,5] The wound healing assay is a commonly used in vitro method to study cell migration, cell interactions, and the underlying mechanisms. [6][7][8][9][10] The conventional "scratch" assay creates a cellfree area or scratch in a cell monolayer using a pipette tip or a pin tool. [10,11] Cells from intact surrounding regions migrate and repopulate the cell-free region over time. The migration rate is measured by observing the decrease in the cellfree area at regular intervals. While the scratch assay is simple and inexpensive, it requires 24-48 h to form a cell monolayer. [11] Moreover, by physically scratching the cell layer with a pipette tip or microneedle, cell-free regions of inconsistent shapes and sizes are created. [10,12,13] This process also damages the underlying plastic surface or extracellular matrix (ECM) substrate, which can significantly affect cell migration. [10,12,13] The electric cell-substrate impedance sensing (ECIS) technique, on the other hand, produces consistent cell-free regions without mechanically disrupting the cell layer. [10,12] In ECIS, a confluent cell layer is formed over a small gold film electrode placed at the bottom of a tissue culture well. Electric pulses are applied to induce cell death at the electrode surface, which creates a well-defined region devoid of cells. [14] However, dead cell fragments can remain on top of the electrode and interfere with cell migration. [12,15] Furthermore, the electric pulses can potentially injure the cells surrounding the electrode, thereby affecting their migration. [10] In contrast to the scratch assay and ECIS, the physical exclusion technique creates cell-free areas of reproducible sizes and shapes with minimal cellular damage. [12,16] This method employs physical barriers, such as plastic inserts or silicone stoppers, to prevent cells from settling in a predefined area. However, it requires 12-20 h to form confluent cellular regions around the barrier. [16,17] Commercial inserts are also expensive and unsuitable for multiple uses. [16] Magnetic levitation is another in vitro technique used to form cell clusters in a migration assay. [18] This method is based on the cellular uptake of biopolymer-encapsulated magnetic In vitro wound healing assays are widely used to investigate cell migration during various physiologic and pathologic processes. However, traditional scratch-based assays produce cell-free areas that are not reproducible, whereas the alternate insert-based exclusion method is expensive and timeconsuming. Here, a rapid, label-free, insert-free magnetic exclusion technique, where magnetic fields are used to create cell-free areas is described. Suspensions of diamagnet...
We present an analytical model that explains the motion of finite-size diamagnetic particles in paramagnetic or diamagnetic fluid media. Our model problem is the magnetic field-assisted three-dimensional assembly of carboxylate microspheres in a gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) solution that is placed in a cuboid. The trajectory of each microparticle is determined through a time marching solution of its equation of motion. The effects of the (1) magnetic field distribution and (2) magnetic susceptibility of the paramagnetic solution, which depends on the Gd-DTPA concentration, on the dynamics of particle assembly are identified. Validation of the analytical model is provided through experimental measurements. For the first time, we demonstrate that it is possible to form structures of diamagnetic particles in diamagnetic fluid media, for which we select the assembly of graphene in water.
Controlled cell assembly is essential for fabricating in vitro 3D models that mimic the physiology of in vivo cellular architectures. Whereas tissue engineering techniques often rely on intrusive magnetic nanoparticles placed in cells and hydrogel encapsulation of cells to produce multilayered cellular constructs, we describe a high-throughput, label-free, and scaffold-free magnetic field-guided technique that assembles cells into a layered aggregate. An inhomogeneous magnetic field influences the diamagnetic cells suspended in a paramagnetic culture medium. Driven by the magnetic susceptibility difference and the field gradient, the cells are displaced toward the region of lowest field strength. Two cell lines are used to demonstrate the sequential assembly of layer-on-layer aggregates in microwells within 6 h. The effect of magnet size on the assembly dynamics is characterized and a microwell size criterion for the highest cell aggregation provided. Label-free magnetic-field-assisted assembly is relevant for on-demand scalable biofabrication of complex layered structures. Potential applications include drug discovery, developmental biology, lab-on-chip devices, and cancer research.
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