Open source acoustofluidics

Acoustic Atomization-Induced Pumping Based on a Vibrating Sharp-Tip Capillary

Pumping is an essential component in many microfluidic applications. Developing simple, small-footprint, and flexible pumping methods is of great importance to achieve truly lab-on-a-chip systems. Here, we report a novel acoustic pump based on the atomization effect induced by a vibrating sharp-tip capillary. As the liquid is atomized by the vibrating capillary, negative pressure is generated to drive the movement of fluid without the need to fabricate special microstructures or use special channel materials. We studied the influence of the frequency, input power, internal diameter (ID) of the capillary tip, and liquid viscosity on the pumping flow rate. By adjusting the ID of the capillary from 30 µm to 80 µm and the power input from 1 V_pp to 5 V_pp, a flow rate range of 3 to 520 µL/min can be achieved. We also demonstrated the simultaneous operation of two pumps to generate parallel flow with a tunable flow rate ratio. Finally, the capability of performing complex pumping sequences was demonstrated by performing a bead-based ELISA in a 3D-printed microdevice.

Degeneration of flow pattern in acousto-elastic flow through sharp-edge microchannels

Acoustic streaming (AS) is the steady time-averaged flow generated by acoustic field, which has been widely used in enhancing mixing and particle manipulation. Current researches on acoustic streaming mainly focus on Newtonian fluids, while many biological and chemical solutions exhibit non-Newtonian properties. The acoustic streaming in viscoelastic fluids has been studied experimentally for the first time in this paper. We found that the addition of polyethylene oxide (PEO) polymer to the Newtonian fluid significantly altered the flow characteristics in the microchannel. The resulting acousto-elastic flow showed two modes: positive mode and negative mode. Specifically, the viscoelastic fluids under acousto-elastic flow exhibit mixing hysteresis features at low flow rates, and degeneration of flow pattern at high flow rates. Through quantitative analysis, the degeneration of flow pattern is further summarized as time fluctuation and spatial disturbance range reduction. The positive mode in acousto-elastic flow can be used for the mixing enhancement of viscoelastic fluids in the micromixer, while the negative mode provides a potential method for particle/cell manipulation in viscoelastic body fluids such as saliva by suppressing unstable flow.

Pumpless deterministic lateral displacement separation using a paper capillary wick

Deterministic lateral displacement (DLD) is a passive separation method that separates particles by hydrodynamic size. This label-free method is a promising technique for cell separation because of its high size resolution and insensitivity to flow rate. Development of capillary-driven microfluidic technologies allows microfluidic devices to be operated without any external power for fluid pumping, lowering their total cost and complexity. Herein, we develop and test a DLD-based particle and cell sorting method that is driven entirely by capillary pressure. We show microchip self-filling, flow focusing, flow stability, and capture of separated particles. We achieve separation efficiency of 92% for particle-particle separation and more than 99% efficiency for cell-particle separation. The high performance of driven flow and separation along with simplicity of the operation and setup make it a valuable candidate for point-of-care devices.

A robot-assisted acoustofluidic end effector

Liquid manipulation is the foundation of most laboratory processes. For macroscale liquid handling, both do-it-yourself and commercial robotic systems are available; however, for microscale, reagents are expensive and sample preparation is difficult. Over the last decade, lab-on-a-chip (LOC) systems have come to serve for microscale liquid manipulation; however, lacking automation and multi-functionality. Despite their potential synergies, each has grown separately and no suitable interface yet exists to link macro-level robotics with micro-level LOC or microfluidic devices. Here, we present a robot-assisted acoustofluidic end effector (RAEE) system, comprising a robotic arm and an acoustofluidic end effector, that combines robotics and microfluidic functionalities. We further carried out fluid pumping, particle and zebrafish embryo trapping, and mobile mixing of complex viscous liquids. Finally, we pre-programmed the RAEE to perform automated mixing of viscous liquids in well plates, illustrating its versatility for the automatic execution of chemical processes.

Integrated Acoustic Chip for Culturing 3D Cell Arrays

Three-dimensional (3D) cell arrays provide an in vitro platform for clinical drug screening, but the bulky culture devices limit their application scenarios. Here, we demonstrate an integrated portable device that can realize contact-free construction of 3D cell spheroids. The interaction between the ultrasound generated by the portable device and the capillary results in periodic pressure nodes or anti-nodes, which lead to form a 3D cell array for cell culture. Such a 3D cell array pattern can be constructed in seconds and requires only 1 μL of cell samples. We further assessed the spheroids formed by the portable device and the impact of the acoustic field on spheroids and demonstrated the drug screening with assembled spheroids. More importantly, the integrated acoustic device can be further integrated with other components for more complex cell culture and all-round analysis. This portable and effective integrated device provides a new avenue for clinical biomedicine.

Laboratory Ozonolysis Using an Integrated Batch-DIY Flow System for Renewable Material Production

Flow chemistry offers a solution for replacing batch methods in chemical preparation where intermediates or products may pose toxicity or instability hazards. Ozonolysis offers an ideal opportunity for flow chemistry solutions, but multiple barriers to entry exist for use of these methods, including equipment cost and performance optimization. To address these challenges, we developed a programmable DIY syringe pump system to use for a continuous flow multireactor process using 3D-printed parts, off-the-shelf stepper motors, and an Arduino microcontroller. Reaction kinetics of ozonide formation informed the use of an integrated batch-flow approach, where ozone addition to an olefin was timed to coincide with fluid movement of a single-syringe pump, followed by downstream Pinnick oxidation and reductive quench in flow. The system was demonstrated by continuous preparation of azelaic acid from ozonolysis of palmitoleic acid, a process limited to low production volumes via batch chemistry. High total production of azelaic acid with 80% yield was obtained from an algae oil sourced unsaturated fatty acid: a product with important applications in medicine, cosmetics, and polymers. This low-cost, scalable approach offers the potential for rapid prototyping and distributed chemical production.

Concentration of Microparticles Using Flexural Acoustic Wave in Sessile Droplets

Acoustic manipulation of microparticles and cells has attracted growing interest in biomedical applications. In particular, the use of acoustic waves to concentrate particles plays an important role in enhancing the detection process by biosensors. Here, we demonstrated microparticle concentration within sessile droplets placed on the hydrophobic surface using the flexural wave. The design benefits from streaming flow induced by the Lamb wave propagated in the glass waveguide to manipulate particles in the droplets. Microparticles will be concentrated at the central area of the droplet adhesion plane based on the balance among the streaming drag force, gravity, and buoyancy at the operating frequency. We experimentally demonstrated the concentration of particles of various sizes and tumor cells. Using numerical simulation, we predicted the acoustic pressure and streaming flow pattern within the droplet and characterized the underlying physical mechanisms for particle motion. The design is more suitable for micron-sized particle preparation, and it can be valuable for various biological, chemical, and medical applications.

Smartphone-microfluidic fluorescence imaging system for studying islet physiology

Smartphone technology has been recently applied for biomedical image acquisition and data analysis due to its high-quality imaging capability, and flexibility to customize multi-purpose apps. In this work, we developed and characterized a smartphone-microfluidic fluorescence imaging system for studying the physiology of pancreatic islets. We further evaluated the system capability by performing real-time fluorescence imaging on mouse islets labeled with either chemical fluorescence dyes or genetically encoded fluorescent protein indicators (GEFPIs). Our results showed that the system was capable of analyzing key beta-cell insulin stimulator-release coupling factors in response to various stimuli with high-resolution dynamics. Furthermore, the integration of a microfluidics allowed high-resolution detection of insulin secretion at single islet level. When compared to conventional fluorescence microscopes and macro islet perifusion apparatus, the system has the advantages of low cost, portable, and easy to operate. With all of these features, we envision that this smartphone-microfluidic fluorescence imaging system can be applied to study islet physiology and clinical applications.

Acousto-Pi: An Opto-Acoustofluidic System Using Surface Acoustic Waves Controlled With Open-Source Electronics for Integrated In-Field Diagnostics

Surface acoustic wave (SAW) devices are increasingly applied in life sciences, biology, and point-of-care applications due to their combined acoustofluidic sensing and actuating properties. Despite the advances in this field, there remain significant gaps in interfacing hardware and control strategies to facilitate system integration with high performance and low cost. In this work, we present a versatile and digitally controlled acoustofluidic platform by demonstrating key functions for biological assays such as droplet transportation and mixing using a closed-loop feedback control with image recognition. Moreover, we integrate optical detection by demonstrating in situ fluorescence sensing capabilities with a standard camera and digital filters, bypassing the need for expensive and complex optical setups. The Acousto-Pi setup is based on open-source Raspberry Pi hardware and 3-D printed housing, and the SAW devices are fabricated with piezoelectric thin films on a metallic substrate. The platform enables the control of droplet position and speed for sample processing (mixing and dilution of samples), as well as the control of temperature based on acousto-heating, offering embedded processing capability. It can be operated remotely while recording the measurements in cloud databases toward integrated in-field diagnostic applications such as disease outbreak control, mass healthcare screening, and food safety.

Generation of programmable dynamic flow patterns in microfluidics using audio signals

Customised audio signals, such as musical notes, can be readily generated by audio software on smartphones and played over audio speakers. Audio speakers translate electrical signals into the mechanical motion of the speaker cone. Coupling the inlet tube to the speaker cone causes the harmonic oscillation of the tube, which in turn changes the velocity profile and flow rate. We employ this strategy for generating programmable dynamic flow patterns in microfluidics. We show the generation of customised rib and vortex patterns through the application of multi-tone audio signals in water-based and whole blood samples. We demonstrate the precise capability to control the number and extent of the ribs and vortices by simply setting the frequency ratio of two- and three-tone audio signals. We exemplify potential applications of tube oscillation for studying the functional responses of circulating immune cells under pathophysiological shear rates. The system is programmable, compact, low-cost, biocompatible, and durable. These features make it suitable for a variety of applications across chemistry, biology, and physics.

Universal Control for Micromotor Swarms with a Hybrid Sonoelectrode

Enabled by active motion of microrobots, conventional biological detection and chemical analyses limited by passive diffusion can be significantly enhanced with fast testing speed and unique sensitiveness. However, controlled release and precise enrichment of microrobot swarms are still difficult to accomplish and thus prohibit them away from practical applications. Here, an efficient and versatile strategy utilizing a needle-shaped hybrid sonoelectrode to disperse and aggregate distinct micromotors is presented, remarkably accelerating mass transfer and enhancing the signal intensity. Hydrogen bubbles generated at the tip of charged electrode can oscillate as actuated by the acoustic field, creating intensified vortexes to disperse micromotors spontaneously. Via removing the attached bubble, the sonoelectrode serving as solid needle isolator is capable of collecting micromotors in a large scale with acoustic streaming in the working reservoir at higher ultrasound frequency. Numerical calculation reveals the streaming profiles with/without microbubbles, and manipulations on classic spherical and tubular micromotor models confirm that the acoustic-powered prototype device is effective for controlling different swarming behaviors in microfluidic channels. Overall, the proposed hybrid sonoelectrode offers a universal and rapid strategy to tailor micromotor swarm behaviors, advancing intelligent microrobots to be featured with active enrichment and compatible for next-generation sensitive portable detection microsystems.

Practical microcircuits for handheld acoustofluidics

Acoustofluidics has promised to enable lab-on-a-chip and point-of-care devices in ways difficult to achieve using other methods. Piezoelectric ultrasonic transducers-as small as the chips they actuate-provide rapid fluid and suspended object transport. Acoustofluidic lab-on-chip devices offer a vast range of benefits in early disease identification and noninvasive drug delivery. However, their potential has long been undermined by the need for benchtop or rack-mount electronics. The piezoelectric ultrasonic transducers within require these equipment and thus acoustofluidic device implementation in a bedside setting has been limited. Here we detail a general process to enable the reader to produce battery or mains-powered microcircuits ideal for driving 1-300 MHz acoustic devices. We include the general design strategy for the circuit, the blocks that collectively define it, and suitable, specific choices for components to produce these blocks. We furthermore illustrate how to incorporate automated resonance finding and tracking, sensing and feedback, and built-in adjustability to accommodate devices' vastly different operating frequencies and powers in a single driver, including examples of fluid and particle manipulation typical of the needs in our discipline. With this in hand, the many groups active in lab-on-a-chip acoustofluidics can now finally deliver on the promise of handheld, point-of-care technologies.

Microfluidic Isolation and Enrichment of Nanoparticles

Over the past decades, nanoparticles have increased in implementation to a variety of applications ranging from high-efficiency electronics to targeted drug delivery. Recently, microfluidic techniques have become an important tool to isolate and enrich populations of nanoparticles with uniform properties (e.g., size, shape, charge) due to their precision, versatility, and scalability. However, due to the large number of microfluidic techniques available, it can be challenging to identify the most suitable approach for isolating or enriching a nanoparticle of interest. In this review article, we survey microfluidic methods for nanoparticle isolation and enrichment based on their underlying mechanisms, including acoustofluidics, dielectrophoresis, filtration, deterministic lateral displacement, inertial microfluidics, optofluidics, electrophoresis, and affinity-based methods. We discuss the principles, applications, advantages, and limitations of each method. We also provide comparisons with bulk methods, perspectives for future developments and commercialization, and next-generation applications in chemistry, biology, and medicine.

Mosaic Immunoassays Integrated with Microfluidic Channels for High-Throughput Parallel Detection

Using the ice-printing technique, we have integrated micromosaic immunoassays (μMIAs) with microfluidic channels, which reduces the sample consumption and response time and allows high-throughput parallel detection. The ice-printing method is a low-temperature and contaminant-free process, which is more convenient, precise, and biofriendly than the traditional fabrication method. Meanwhile, based on the ice-drying process, this method can obtain a uniform distribution of the residue protein patterns, which leads to a uniform fluorescence result. As a proof of concept, the test of stability, sensitivity, and specificity of μMIA based on one-step ELISA are demonstrated. In this device, immobilized antigens surrounded with ice could remain biological at -20 °C for months.

Low-frequency flexural wave based microparticle manipulation

Manipulation of microparticles and bio-samples is a critical task in many research and clinical settings. Recently, acoustic based methods have garnered significant attention due to their relatively simple designs, and biocompatible and precise manipulation of small objects. Herein, we introduce a flexural wave based acoustofluidic manipulation platform that utilizes low-frequency (4-6 kHz) commercial buzzers to achieve dynamic particle concentration and translation in an open fluid well. The device has two primary modes of functionality, wherein particles can be concentrated in pressure nodes that are present on the bottom surface of the device, or particles can be trapped and manipulated in streaming vortices within the fluid domain; both of these functions result from flexural mode vibrations that travel from the transducers throughout the device. Throughout our research, we numerically and experimentally explored the wave patterns generated within the device, investigated the particle concentration phenomenon, and utilized a phase difference between the two transducers to achieve precision movement of fluid vortices and the entrapped particle clusters. With its simple, low-cost nature and open fluidic chamber design, this platform can be useful in many biological, biochemical, and biomedical applications, such as tumor spheroid generation and culture, as well as the manipulation of embryos.

An acoustofluidic device for efficient mixing over a wide range of flow rates

Whether reagents and samples need to be combined to achieve a desired reaction, or precise concentrations of solutions need to be mixed and delivered downstream, thorough mixing remains a critical step in many microfluidics-based biological and chemical assays and analyses. To achieve complete mixing of fluids in microfluidic devices, researchers have utilized novel channel designs or active intervention to facilitate mass transport and exchange of fluids. However, many of these solutions have a major limitation: their design inherently limits their operational throughput; that is, different designs work at specific flow rates, whether that be low or high ranges, but have difficulties outside of their tailored design regimes. In this work, we present an acoustofluidic mixer that is capable of achieving efficient, thorough mixing across a broad range of flow rates (20-2000 μL min-1) using a single device. Our mixer combines active acoustofluidic mixing, which is responsible for mixing fluids at lower flow rates, with passive hydrodynamic mixing, which accounts for mixing fluids at higher flow rates. The mechanism, functionality, and performance of our acoustofluidic device are both numerically and experimentally validated. Additionally, the real-world potential of our device is demonstrated by synthesizing polymeric nanoparticles with comparable sizes over a two-order-of-magnitude wide range of flow rates. This device can be valuable in many biochemical, biological, and biomedical applications. For example, using our platform, one may synthesize nanoparticles/nanomaterials at lower flow rates to first identify optimal synthesis conditions without having to waste significant amounts of reagents, and then increase the flow rate to perform high-throughput synthesis using the optimal conditions, all using the same single device and maintaining performance.

A Cell-Phone-Based Acoustofluidic Platform for Quantitative Point-of-Care Testing

Acoustofluidic methods, with advantages including simplicity of device design, biocompatible manipulation, and low power consumption, have been touted as promising tools for point-of-care (POC) testing. Here, we report a cell-phone-based acoustofluidic platform that uses acoustic radiation forces to enrich nanoscale analytes and red and green fluorescence nanoparticles (SiO₂@R and G@SiO₂) as probes for POC visual testing. Thus, the color signals from the fluorescent probes are enhanced, and colorimetric sensitivity is significantly improved. As a POC demonstration, the acoustofluidic platform is used to detect hemoglobin (Hb) from human blood, resulting in a rapid and straightforward measurement of normal blood Hb levels. Combining an acoustofluidic-based nanoparticle-concentration platform with cell-phone-based colorimetry, our method introduces a potential pathway toward practical POC testing.

Acoustofluidic methods in cell analysis

Cellular analysis is a central concept for both biology and medicine. Over the past two decades, acoustofluidic technologies, which marry acoustic waves with microfluidics, have significantly contributed to the development of innovative approaches for cellular analysis. Acoustofluidic technologies enable precise manipulations of cells and the fluids that confine them, and these capabilities have been utilized in many cell analysis applications. In this review article, we examine various applications where acoustofluidic methods have been implemented, including cell imaging, cell mechanotyping, circulating tumor cell phenotyping, sample preparation in clinics, and investigation of cell-cell interactions and cell-environment responses. We also provide our perspectives on the technological advantages, limitations, and potential future directions for this innovative field of methods.