Sheathless Size-Based Acoustic Particle Separation

Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In this paper, we present a microfluidic platform for sheathless particle separation using standing surface acoustic waves. In this platform, particles are first lined up at the center of the channel without introducing any external sheath flow. The particles are then entered into the second stage where particles are driven towards the off-center pressure nodes for size based separation. The larger particles are exposed to more lateral displacement in the channel due to the acoustic force differences. Consequently, different-size particles are separated into multiple collection outlets. The prominent feature of the present microfluidic platform is that the device does not require the use of the sheath flow for positioning and aligning of particles. Instead, the sheathless flow focusing and separation are integrated within a single microfluidic device and accomplished simultaneously. In this paper, we demonstrated two different particle size-resolution separations; (1) 3 µm and 10 µm and (2) 3 µm and 5 µm. Also, the effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. These technologies have potential to impact broadly various areas including the essential microfluidic components for lab-on-a-chip system and integrated biological and biomedical applications.Bankhead-Coley Florida Cancer Research Program (Grant # 1BN04-34183)National Science Foundation (U.S.) (Grant 0968736)National Science Foundation (U.S.) (Grant 1135419)National Science Foundation (U.S.) (Grant 1056475

Inertio- and Elasto-Magnetic Fractionation of Multiple Microparticles in Newtonian and Non-Newtonian Fluid

Sorting of microparticles and cells using microfluidic platforms has several applications in diagnosis, biotechnology, and medicine. However, the currently available microfluidic sorting techniques have one or more of the following drawbacks such as low throughput, need for diluting sheath flows for operating devices, inability to sort multiple particles simultaneously, low purity and requirement of complicated fabrication methods. In this thesis, a hybrid scheme for sheath-less fractionation of microparticles has been devised by integrating magnetophoresis, inertial focusing and elastic focusing approaches with the concept of pinched flow fractionation. We have taken advantage of inertia, magnetic, drag, and elastic forces to achieve high throughput multiplexed microparticle fractionation. The technique has been tested with respect to parameters such as size of particles, flow rate, device geometry and fluid viscosity (Newtonian vs. non-Newtonian). This sorting method offers a tool to handle heterogeneous samples and can be used for affinity-based immune-magnetic separation of biological substances

Microfluidic particle separation via elasto-inertial focusing in straight rectangular microchannels

Label-free separation of target particles or cells in a continuous flow is a crucial process in many commercial and industrial applications. Among the various particle and cell separation techniques, microfluidic separator based on elasto-inertial forces in the flow of non-Newtonian fluids has received increasing attention in the past decade. However, current studies have been mainly focused upon the use of viscoelastic forces to manipulate particles and cells. Little work has been done to obtain a fundamental understanding on how the fluid rheological properties, such as viscoelasticity and shear thinning, affect the motion of particles. This dissertation is aimed to address this question through a systematic experimental study. We first designed a series of experiments to study both the individual and combined effects of fluid rheology and inertia on the migration of rigid spherical particles in a (nearly) square microchannel. The sole effects of fluid inertia, elasticity and shear thinning were investigated by re-suspending the same particles into Newtonian (water), purely elastic (polyvinylpyrrolidone, PVP) and inelastic shear thinning (xanthan gum, XG) fluids, respectively. The combined effects of fluid elasticity and inertia or fluid shear thinning and inertia were investigated in the flow of PVP and XG solutions over a wide range of flow rates. The combined effects of fluid elasticity, shear thinning, and inertia were investigated in two types of elastic fluids with varying shear-thinning properties (polyethylene oxide, PEO and polyacrylamide, PAA). We found that fluid elasticity directs particles toward the channel centerline while fluid shear thinning causes particles to migrate towards both the centerline and corners. In the second part of this dissertation, we performed a comprehensive study of the separation of particles and cells in the flow of PEO solutions through straight rectangular microchannels. We investigated the effects of flow rate, solvent viscosity, PEO concentration, and channel height on the elasto-inertial separation of spherical polystyrene particles. We proposed to explain the observed elasto-inertial particle focusing using a competition of center- (because of fluid elasticity) and wall- (because of fluid shear thinning) directed viscoelastic forces. We also applied this sheath-free separation technique in the flow of biocompatible PEO solutions to sort drug-treated Cryptococcus neoformans by morphology. Three metrics were used to evaluate the parametric effects on the cell separation performance: efficiency, purity, and enrichment ratio. In the last part of this dissertation, we performed another systematic experimental study of the motion of rigid spherical particles in the flow of inelastic shear-thinning XG solutions through straight rectangular microchannels. We found that the number and location of equilibrium particles position are both a strong function of channel dimension, particle size, and XG concentration. Inspired by this study, we demonstrated for the first time a continuous sheath-free separation of polystyrene particles in XG solutions through a straight high width/depth-ratio microchannel. This separation was found to remain effective over a much wider range of flow rates than those reported in the flow of viscoelastic fluids. We attempted to explain the particle migrations in XG solutions using the competition of a strong wall-directed (because of the strong shear thinning effect) and a weak center-directed (because of the weak elasticity effect) lateral force induced by normal stresses in a Poiseuille flow

Acoustic Microfluidic Separation Techniques and Bioapplications: A Review

Microfluidic separation technology has garnered significant attention over the past decade where particles are being separated at a micro/nanoscale in a rapid, low-cost, and simple manner. Amongst a myriad of separation technologies that have emerged thus far, acoustic microfluidic separation techniques are extremely apt to applications involving biological samples attributed to various advantages, including high controllability, biocompatibility, and non-invasive, label-free features. With that being said, downsides such as low throughput and dependence on external equipment still impede successful commercialization from laboratory-based prototypes. Here, we present a comprehensive review of recent advances in acoustic microfluidic separation techniques, along with exemplary applications. Specifically, an inclusive overview of fundamental theory and background is presented, then two sets of mechanisms underlying acoustic separation, bulk acoustic wave and surface acoustic wave, are introduced and discussed. Upon these summaries, we present a variety of applications based on acoustic separation. The primary focus is given to those associated with biological samples such as blood cells, cancer cells, proteins, bacteria, viruses, and DNA/RNA. Finally, we highlight the benefits and challenges behind burgeoning developments in the field and discuss the future perspectives and an outlook towards robust, integrated, and commercialized devices based on acoustic microfluidic separation

Acoustic Forces in Cytometry and Biomedical Applications: Multidimensional Acoustophoresis

Over the last decades the ongoing work in the fields of Lab-on-a-Chip and Micro-Total-Analysis-Systems has led to the discovery of new or improved ways to handle and analyse small volumes of biofluids and complex biosuspensions. The benefits of working on the microscale include: miniaturization of the analysis systems with less need for large sample volumes; temporal and spatial control of suspended particle/cell positions; low volume sheath flow lamination or mixing; novel separation techniques by using forces inherent to the microscale domain; precise regulation of sample temperatures and rapid analysis with less volumes needed to be processed. Researchers now seek to implement these techniques in integrated systems to benefit the biomedical research field as well as clinics. Acoustophoresis, a method that utilizes acoustic forces to move particles and cells in microfluidic channels has been gaining increased attention over the last decade. The acoustophoretic method has been shown to handle a number of biosuspensions e.g., blood, cell cultures and raw milk as well as other biofluids, and comes with a variety of available unit operations e.g., free flow separation, binary density separation, particle positioning, contactless trapping, buffer changes, washing, and surface chemistry based sorting that allows integration into a wide range of application. The theoretical and experimental understanding of the acoustic radiation force which is the principal force used to manipulate particles in these systems (often generated with standing waves) has also evolved during this time. Chip-based acoustic systems have been presented in e.g., silicon, glass and PDMS, further illustrating the versatility of the method. This dissertation presents some of the recent developments in the acoustophoretic field to illustrate how acoustic forces can be used in cytometry and biomedical applications, specifically by utilizing multiple acoustic wavelength geometries or two-dimensional particle manipulation. Paper I presents a novel way to pretreat raw milk in order to facilitate rapid quality control. Paper II extends this method by presenting a technique for label free cytometry in raw milk. Paper III showcases the ability to sort particles with fluorescence activated acoustic forces. Paper IV presents a low complexity high precision proof-of-concept sheathless impedance cytometer that can be integrated in other chip based systems. Paper V presents an improved method for concurrent blood component fractionation that requires less manual handling compared to established methods by implementing free flow separation into multiple outlets. The theory section explains the underlying physical laws that govern the microscale fluid systems presented here. Acoustic force theory is explained in detail for better understanding of the acoustic radiation forces that act on the suspended particles and also cause media streaming. The particle manipulation section compares the different methods that are available to researchers in the biomedical microfluidic field. The microfabrication section deals with the design aspects of using various materials. Unit operations and applications specific for acoustophoresis are presented. Biofluids and cell types including blood and raw milk are discussed to underline the challenges that researchers are faced with during system design, handling and analysis. The aim of this dissertation is to provide a foundation for future development of acoustic force applications in cytometry and biomedicine

Contactless acoustic micro/nano manipulation:a paradigm for next generation applications in life sciences

Acoustic actuation techniques offer a promising tool for contactless manipulation of both synthetic and biological micro/nano agents that encompass different length scales. The traditional usage of sound waves has steadily progressed from mid-air manipulation of salt grains to sophisticated techniques that employ nanoparticle flow in microfluidic networks. State-of-the-art in microfabrication and instrumentation have further expanded the outreach of these actuation techniques to autonomous propulsion of micro-agents. In this review article, we provide a universal perspective of the known acoustic micromanipulation technologies in terms of their applications and governing physics. Hereby, we survey these technologies and classify them with regards to passive and active manipulation of agents. These manipulation methods account for both intelligent devices adept at dexterous non-contact handling of micro-agents, and acoustically induced mechanisms for self-propulsion of micro-robots. Moreover, owing to the clinical compliance of ultrasound, we provide future considerations of acoustic manipulation techniques to be fruitfully employed in biological applications that range from label-free drug testing to minimally invasive clinical interventions

Passive Dielectrophoretic Focusing of Particles and Cells in Ratchet Microchannels.

Focusing particles into a tight stream is critical for many microfluidic particle-handling devices such as flow cytometers and particle sorters. This work presents a fundamental study of the passive focusing of polystyrene particles in ratchet microchannels via direct current dielectrophoresis (DC DEP). We demonstrate using both experiments and simulation that particles achieve better focusing in a symmetric ratchet microchannel than in an asymmetric one, regardless of the particle movement direction in the latter. The particle focusing ratio, which is defined as the microchannel width over the particle stream width, is found to increase with an increase in particle size or electric field in the symmetric ratchet microchannel. Moreover, it exhibits an almost linear correlation with the number of ratchets, which can be explained by a theoretical formula that is obtained from a scaling analysis. In addition, we have demonstrated a DC dielectrophoretic focusing of yeast cells in the symmetric ratchet microchannel with minimal impact on the cell viability