Deformation-based cell separation has emerged recently as an effective approach to isolate cells that have similar size but different deformability and thus exhibits potential applications in disease diagnostic including circulating cancer cells and sickle cell anemia. However, key physical parameters that regulate deformation-based cell separation remain unclear. Here we developed a microfluidic approach in a droplet-based model system to explore the effect of physical parameters of droplets including size, viscosity, and velocity on deformation-based separation. We fabricated microfluidic devices that had a straight flow-focusing channel, a cylindrical post, two inlets and three outlets and studied droplet sorting at different channel dimensions and flow rate. We showed that decreasing viscosity or increasing velocity of droplets would result in decreasing the effective size of droplets in droplet sorting. The results showed that droplets with a large size or high viscosity were sorted to side outlets at low velocity in the microfluidic device whereas droplets with a small size or low viscosity exited through the center outlet at high velocity. Such separation was determined by the characteristic distance ([delta]) and impact angle ([theta]) during a two-step sequential droplet deformation process. The droplets were sorted to the side outlets when [delta] ≥ 0.542 or [theta] ≥ 28°, and the droplet exited through the center outlet when [delta] ≤ 0.525 or [theta] ≤ 28°. We then further tested the dependence of [delta] and [theta] on cell sorting using RPF-HUVECs and showed that with cells up to the characteristic distance [delta] = 0.419 tested in the experiment, all exited through the center outlet. [theta] measurement was skipped for all the cells exiting through the center outlet because it was not applicable. Future studies of the role of [delta] and [theta] in cell sorting however is needed by optimizing the geometric parameters of the microfluidic device, i.e., gap distance, channel width, post diameter. With properly designed microfluidic device, this microfluidic approach is expected to provide a way for conducting fast, low-cost, and efficient cell analysis that would benefit future disease diagnostics.

The manipulation of cells and microparticles within microfluidic systems using external forces is valuable for many microscale analytical and bioanalytical applications. Acoustofluidics is the ultrasound-based external forcing of microparticles with microfluidic systems. It has gained much interest because it allows for the simple label-free separation of microparticles based on their mechanical properties without affecting the microparticles themselves. Microscale Acoustofluidics provides an introduction to the field providing the background to the fundamental physics including chapters on governing equations in microfluidics and perturbation theory and ultrasound resonances, acoustic radiation force on small particles, continuum mechanics for ultrasonic particle manipulation, and piezoelectricity and application to the excitation of acoustic fields for ultrasonic particle manipulation. The book also provides information on the design and characterization of ultrasonic particle manipulation devices as well as applications in acoustic trapping and immunoassays. Written by leading experts in the field, the book will appeal to postgraduate students and researchers interested in microfluidics and lab-on-a-chip applications.

This book delves into the recent developments in the microscale and microfluidic technologies that allow manipulation at the single and cell aggregate level. Expert authors review the dominant mechanisms that manipulate and sort biological structures, making this a state-of-the-art overview of conventional cell sorting techniques, the principles of microfluidics, and of microfluidic devices. All chapters highlight the benefits and drawbacks of each technique they discuss, which include magnetic, electrical, optical, acoustic, gravity/sedimentation, inertial, deformability, and aqueous two-phase systems as the dominant mechanisms utilized by microfluidic devices to handle biological samples. Each chapter explains the physics of the mechanism at work, and reviews common geometries and devices to help readers decide the type of style of device required for various applications. This book is appropriate for graduate-level biomedical engineering and analytical chemistry students, as well as engineers and scientists working in the biotechnology industry.

Microfluidic platforms are increasingly being used for separating a wide variety of particles based on their physical and chemical properties. In the past two decades, many practical applications have been found in chemical and biological sciences, including single cell analysis, clinical diagnostics, regenerative medicine, nanomaterials synthesis, environmental monitoring, etc. In this Special Issue, we invited contributions to report state-of-the art developments in the fields of micro- and nanofluidic separation, fractionation, sorting, and purification of all classes of particles, including, but not limited to, active devices using electric, magnetic, optical, and acoustic forces; passive devices using geometries and hydrodynamic effects at the micro/nanoscale; confined and open platforms; label-based and label-free technology; and separation of bioparticles (including blood cells), circulating tumor cells, live/dead cells, exosomes, DNA, and non-bioparticles, including polymeric or inorganic micro- and nanoparticles, droplets, bubbles, etc. Practical devices that demonstrate capabilities to solve real-world problems were of particular interest.

This book summarizes the various microfluidic-based approaches for single-cell capture, isolation, manipulation, culture and observation, lysis, and analysis. Single-cell analysis reveals the heterogeneities in morphology, functions, composition, and genetic performance of seemingly identical cells, and advances in single-cell analysis can overcome the difficulties arising due to cell heterogeneity in the diagnostics for a targeted model of disease. This book provides a detailed review of the state-of-the-art techniques presenting the pros and cons of each of these methods. It also offers lessons learned and tips from front-line investigators to help researchers overcome bottlenecks in their own studies. Highlighting a number of techniques, such as microfluidic droplet techniques, combined microfluidics-mass-spectrometry systems, and nanochannel sampling, it describes in detail a new microfluidic chip-based live single-cell extractor (LSCE) developed in the editor’s laboratory, which opens up new avenues to use open microfluidics in single-cell extraction, single-cell mass spectrometric analysis, single-cell adhesion analysis and subcellular operations. Serving as both an elementary introduction and advanced guidebook, this book interests and inspires scholars and students who are currently studying or wish to study microfluidics-based cell analysis methods.

Droplet microfluidics has dramatically developed in the past decade and has been established as a microfluidic technology that can translate into commercial products. Its rapid development and adoption have relied not only on an efficient stabilizing system (oil and surfactant), but also on a library of modules that can manipulate droplets at a high-throughput. Droplet microfluidics is a vibrant field that keeps evolving, with advances that span technology development and applications. Recent examples include innovative methods to generate droplets, to perform single-cell encapsulation, magnetic extraction, or sorting at an even higher throughput. The trend consists of improving parameters such as robustness, throughput, or ease of use. These developments rely on a firm understanding of the physics and chemistry involved in hydrodynamic flow at a small scale. Finally, droplet microfluidics has played a pivotal role in biological applications, such as single-cell genomics or high-throughput microbial screening, and chemical applications. This Special Issue will showcase all aspects of the exciting field of droplet microfluidics, including, but not limited to, technology development, applications, and open-source systems.

In this thesis, a new microfluidic device is presented for sorting of deformable particles based on the hydrodynamic resistance induced in a microchannel. Hydrodynamic resistance can be related to physical properties, including size and deformability of the particle, and can also be influenced by particle-wall interactions, hence allowing sorting based on any of these characteristics. This device could find application in cell sorting and bioseparation for therapeutics, research, and point-of-care diagnostics, as well as in sorting of droplets and emulsions for research and industrial applications (e.g., pharmaceutics, food industry, etc.). The device design is carried out using an equivalent resistance model, and numerical simulations are used to validate the design. The device is fabricated in PDMS, flow velocities are characterized using particle streak velocimetry, and sorting experiments are conducted to sort deformable gelatin particles according to size, and droplets of water and glycerol according to deformability. A sorting resolution of approximately 1 pm was obtained when sorting based on size, and droplets of water and glycerol were sorted into separate streams when sorting based on deformability. The main strength of the device over existing technology lies in its simplicity: sorting is carried out passively in the microfluidic circuit, eliminating the need for additional detection or sorting modules. Moreover, the device could be easily customized to change the sorting parameter or the sorting threshold, and multiple devices can be combined in parallel (to increase throughput) or in series (to increase resolution).