Circulating tumor cells (CTCs) are rare cancer cells that are shed from primary or metastatic tumors into the peripheral blood circulation. Phenotypic and genetic characterization of these rare cells can provide important information to guide cancer staging and treatment, and thus further research into their characteristics and properties is an area of considerable interest. In this protocol, we describe detailed procedures for the production and use of a label-free spiral microfluidic device to allow size-based isolation of viable CTCs using hydrodynamic forces that are present in curvilinear microchannels. This spiral system enables us to achieve ≥ 85% recovery of spiked cells across multiple cancer cell lines and 99.99% depletion of white blood cells in whole blood. The described spiral microfluidic devices can be produced at an extremely low cost using standard microfabrication and soft lithography techniques (2-3 d), and they can be operated using two syringe pumps for lysed blood samples (7.5 ml in 12.5 min for a three-layered multiplexed chip). The fast processing time and the ability to collect CTCs from a large patient blood volume allows this technique to be used experimentally in a broad range of potential genomic and transcriptomic applications.

Microfiltration is a ubiquitous and often crucial part of many industrial processes, including biopharmaceutical manufacturing. Yet, all existing filtration systems suffer from the issue of membrane clogging, which fundamentally limits the efficiency and reliability of the filtration process. Herein, we report the development of a membrane-less microfiltration system by massively parallelizing inertial microfluidics to achieve a macroscopic volume processing rates (~ 500 mL/min). We demonstrated the systems engineered for CHO (10–20 μm) and yeast (3–5 μm) cells filtration, which are two main cell types used for large-scale bioreactors. Our proposed system can replace existing filtration membrane and provide passive (no external force fields), continuous filtration, thus eliminating the need for membrane replacement. This platform has the desirable combinations of high throughput, low-cost, and scalability, making it compatible for a myriad of microfiltration applications and industrial purposes.

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Nanomagnetic force stimulation with ferromagnetic nanoparticles was found to trigger calcium influx in cortical neural networks without observable cytotoxicity. Stimulated neural networks showed an average of 20% increment in calcium fluorescence signals and a heightened frequency in calcium spiking. These effects were also confined spatially to areas with engineered high magnetic field gradients. Furthermore, blockage of N-type calcium channels inhibited the stimulatory effects of the nanomagnetic forces, suggesting the role of mechano-sensitive ion channels in mediating calcium influx.

Diagnosis of malaria at the early stage of infection is challenging due to the difficulty in detecting low abundance parasites from blood. Molecular methods such as real-time polymerase chain reaction (qPCR) can be especially useful for detecting low parasitemia levels due to their high sensitivity and their ability to recognize different malarial species and strains. Unfortunately, the accuracy of qPCR-based malaria detection can be compromised by many factors, including the limited specificity of primers, presence of PCR inhibitors in blood serum and DNA contamination from nucleated blood cells. Here, we use a label-free, shear-modulated inertial microfluidic system to enrich malaria parasites from blood so as to facilitate a more reliable and specific PCR-based malaria detection. This technique capitalizes on cell focusing behaviors in high aspect ratio microchannels coupled with pinched flow dynamics to isolate ring-stage malaria parasites from lysed blood containing white blood cells (WBCs). In this high aspect ratio (ratio of the channel height to the width) platform, the high shear rate along the channel width causes the dispersed WBCs at the inlet to migrate and align into two streams near the channel sidewalls while the malaria parasites remain unfocused. Sensitive detection of parasites at spiked densities ranging from 10(3) to 10(4)Plasmodium falciparum parasites per mL (~2-10 per μL) has been demonstrated; they have also been quantified in whole blood using qPCR. This is approximately 100-fold more sensitive than the gold standard conventional microscopy analysis of thick blood smears. The simplicity of this device makes it ideal for integration with an automatic system for ultra-fast and accurate detection despite low levels of parasitemia. It can also help in malaria screening and elimination efforts.

Microfluidic cell-separation technologies have been studied for almost two decades, but the limited throughput has restricted their impact and range of application. Recent advances in microfluidics enable high-throughput cell sorting and separation, and this has led to various novel diagnostic and therapeutic applications that previously had been impossible to implement using microfluidics technologies. In this review, we focus on recent progress made in engineering large-volume microfluidic cell-sorting methods and the new applications enabled by them.

Techniques offering remote control of neural activity with high spatiotemporal resolution and specificity are invaluable for deciphering the physiological roles of different classes of neurons in brain development and disease. Here, we first confirm that microfabricated substrates with enhanced magnetic field gradients allow for wireless stimulation of neural circuits dosed with magnetic nanoparticles using calcium indicator dyes. We also investigate the mechanism of mechano-transduction in this system and identify that N-type mechano-sensitive calcium ion channels play a key role in signal generation in response to magnetic force. We next applied this method for chronic stimulation of a fragile X syndrome (FXS) neural network model and found that magnetic force-based stimulation modulated the expression of mechano-sensitive ion channels which are out of equilibrium in a number of neurological diseases including FXS. This technique can serve as a tool for acute and chronic modulation of endogenous ion channel expression in neural circuits in a spatially localized manner to investigate a number of disease processes in the future.

Neuromodulation tools are useful to decipher and modulate neural circuitries implicated in functions and diseases. Existing electrical and chemical tools cannot offer specific neural modulation while optogenetics has limitations for deep tissue interfaces, which might be overcome by miniaturized optoelectronic devices in the future. Here, a 3D magnetic hyaluronic hydrogel is described that offers noninvasive neuromodulation via magnetomechanical stimulation of primary dorsal root ganglion (DRG) neurons. The hydrogel shares similar biochemical and biophysical properties as the extracellular matrix of spinal cord, facilitating healthy growth of functional neurites and expression of excitatory and inhibitory ion channels. By testing with different neurotoxins, and micropillar substrate deflections with electrophysical recordings, it is found that acute magnetomechanical stimulation induces calcium influx in DRG neurons primarily via endogenous, mechanosensitive TRPV4 and PIEZO2 channels. Next, capitalizing on the receptor adaptation characteristic of DRG neurons, chronic magnetomechanical stimulation is performed and found that it reduces the expression of PIEZO2 channels, which can be useful for modulating pain where mechanosensitive channels are typically overexpressed. A general strategy is thus offered for neuroscientists and material scientists to fabricate 3D magnetic biomaterials tailored to different types of excitable cells for remote magnetomechanical modulation.