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Here, we demonstrate a modular, reconfigurable, and self-sufficient convective heat exchanger for regulation of temperature in microfluidic systems. The heat exchanger consists of polymer tubes wrapped around a plastic pole and fully embedded in an elastomer block, which can be easily mounted onto the microfluidic structure. It is compatible with various microfluidic geometries and materials. Miniaturized, battery-powered piezoelectric pumps are utilized to drive the heat carrying liquid through the heat exchanger at desired flow rates and temperatures. Customized temperature profiles can be generated by changing the configuration of the heat exchanger with respect to the microfluidic structure. Tailored dynamic temperature profiles can be generated by changing the temperature of the heat carrying liquid in successive cycles. This feature is used to study the calcium signaling of endothelial cells under successive temperature cycles of 24 to 37 °C. The versatility, simplicity, and self-sufficiency of the heat exchanger makes it suitable for various microfluidic based cellular assays.

We describe a piezoelectric pumping system for studying the mechanobiology of human aortic endothelial cells (HAECs) under pulsatile flow in microfluidic structures. The system takes advantage of commercially available components, including pumps, flow sensors, and microfluidic channels, which can be easily integrated, programmed, and operated by cellular biologists. Proof-of-concept experiments were performed to elucidate the complex mechanotransduction processes of endothelial cells to pulsatile flow. In particular, we investigated the effect of atheroprone and atheroprotective pulsatile shear stress on endothelial cytoskeleton remodeling and distribution of β-catenin, as well as nuclear shape and size. The system is simple to operate, relatively inexpensive, portable, and controllable, providing opportunities for studying the mechanobiology of endothelial cells using microfluidic technologies.

Here, we demonstrate a multilayered microfluidic system integrated with commercially available polymer tubes for controlling the temperature of the sample under various static and dynamic conditions. Highly controllable temperature profiles can be produced by modulating the flow rate or inlet temperature of the water passing through the tubes. Customised temperature gradients can be created across the length or width of a channel by mismatching the inlet temperature of the tubes. Temperature cycles can also be produced by repeatedly switching the tubes between hot and cold flasks. Proof-of-concept experiments demonstrate the utility of this system for studying the drug-induced calcium signaling of human monocytes under dynamic thermal conditions. The versatility and simplicity of our system provides opportunities for studying temperature-sensitive chemical, biochemical, and biological samples under various operating conditions.

Nonviable cells are essential biosystems, due to the functionalities they offer and their effects on viable cells. Therefore, the separation and immobilization of nonviable cells separately or in the vicinity of viable cells is of great importance for many fundamentals investigations in cell biology. However, most nonviable cells become less polarizable than the surrounding medium at conductivities above 0.01 S/m. This means that in such a medium, dielectrophoresis, despite its great versatilities for manipulation of cells, cannot be employed for immobilizing nonviable cells. Here, we present a novel approach to change the dielectrophoretic (DEP) response of nonviable yeast cells by treating them with low concentrations of ionic surfactants such as sodium dodecyl sulfate. After this treatment, they exhibit a strong positive DEP response, even at high medium conductivities. The capability of this treatment is demonstrated in two proof-of-concept experiments. First, we show the sorting and immobilization of viable and nonviable yeast cells, along consecutive microelectrode arrays. Second, we demonstrate the immobilization of viable and nonviable cells in the vicinity of each other along the same microelectrode array. The proposed technique allows DEP platforms to be utilized for the immobilization and subsequent postanalysis of both viable and nonviable cells with and without the presence of each other.

Development of the dielectrophoretic (DEP) live cell trapping technology and its interfacing with the environmental scanning electron microscopy (ESEM) is described. DEP microelectrode arrays were fabricated on glass substrate using photolithography and lift-off. Chip-based arrays were applied for ESEM analysis of DEP-trapped human leukemic cells. This work provides proof-of-concept interfacing of the DEP cell retention and trapping technology with ESEM to provide a high-resolution analysis of individual nonadherent cells.

Quantification of programmed and accidental cell death provides useful end-points for the anticancer drug efficacy assessment. Cell death is, however, a stochastic process. Therefore, the opportunity to dynamically quantify individual cellular states is advantageous over the commonly employed static, end-point assays. In this work, we describe the development and application of a microfabricated, dielectrophoretic (DEP) cell immobilization platform for the real-time analysis of cancer drug-induced cytotoxicity. Microelectrode arrays were designed to generate weak electro-thermal vortices that support efficient drug mixing and rapid cell immobilization at the delta-shape regions of strong electric field formed between the opposite microelectrodes. We applied this technology to the dynamic analysis of hematopoietic tumor cells that represent a particular challenge for real-time imaging due to their dislodgement during image acquisition. The present study was designed to provide a comprehensive mechanistic rationale for accelerated cell-based assays on DEP chips using real-time labeling with cell permeability markers. In this context, we provide data on the complex behavior of viable vs dying cells in the DEP fields and probe the effects of DEP fields upon cell responses to anticancer drugs and overall bioassay performance. Results indicate that simple DEP cell immobilization technology can be readily applied for the dynamic analysis of investigational drugs in hematopoietic cancer cells. This ability is of particular importance in studying the outcome of patient derived cancer cells, when exposed to therapeutic drugs, as these cells are often rare and difficult to collect, purify and immobilize.

The localized motion of cells within a cluster is an important feature of living organisms and has been found to play roles in cell signaling, communication, and migration, thus affecting processes such as proliferation, transcription, and organogenesis. Current approaches for inducing dynamic movement into cells, however, focus predominantly on mechanical stimulation of single cells, affect cell integrity, and, more importantly, need a complementary mechanism to pattern cells. In this article, we demonstrate a new strategy for the mechanical stimulation of large cell clusters, taking advantage of dielectrophoresis. This strategy is based on the cellular spin resonance mechanism, but it utilizes coating agents, such as bovine serum albumin, to create consistent rotation and vibration of individual cells. The treatment of cells with coating agents intensifies the torque induced on the cells while reducing the friction at the cell-cell and cell-substrate interfaces, resulting in the consistent motion of the cells. Such localized motion can be modulated by varying the frequency and voltage of the applied sinusoidal AC signal and can be achieved in the absence and presence of flow. This strategy enables the survival and functioning of moving cells within large-scale clusters to be investigated.

We demonstrate an active microfluidic platform that integrates dielectrophoresis for the control of silver nanoparticles spacing, as they flow in a liquid channel. By careful control of the nanoparticles spacing, we can effectively increase the surface-enhanced Raman scattering (SERS) signal intensity based on augmenting the number of SERS-active hot-spots, while avoiding irreversible aggregation of the particles. The system is benchmarked using dipicolinate (2,6-pyridinedicarboxylic acid) (DPA), which is a biomarker of Bacillus anthracis. The validity of the results is discussed using several complementing characterization scenarios.