Separation of platelets from whole blood using standing surface acoustic waves in a microchannel

Evaluation of Acoustophoretic and Dielectrophoretic Forces for Droplet Injection in Droplet-Based Microfluidic Devices

Acoustophoretic forces have been successfully implemented into droplet-based microfluidic devices to manipulate droplets. These acoustophoretic forces in droplet microfluidic devices are typically generated as in acoustofluidic devices through transducer actuation of a piezoelectric substrate such as lithium niobate (LiNbO3), which is inherently accompanied by the emergence of electrical fields. Understanding acoustophoretic versus dielectrophoretic forces produced by electrodes and transducers within active microfluidic devices is important for the optimization of device performance during design iterations. In this case study, we design microfluidic devices with a droplet injection module and report an experimental strategy to deduce the respective contribution of the acoustophoretic versus dielectrophoretic forces for the observed droplet injection. Our PDMS-based devices comprise a standard oil-in-water droplet-generating module connected to a T-junction injection module featuring actuating electrodes. We use two different electrode geometries produced within the same PDMS slab as the droplet production/injection channels by filling low-melting-point metal alloy into channels that template the electrode geometries. When these electrodes are constructed on LiNbO3 as the substrate, they have a dual function as a piezoelectric transducer, which we call embedded liquid metal interdigitated transducers (elmIDTs). To decipher the contribution of acoustophoretic versus dielectrophoretic forces, we build the same devices on either piezoelectric LiNbO3 or nonpiezo active glass substrates with different combinations of physical device characteristics (i.e., elmIDT geometry and alignment) and operate in a range of phase spaces (i.e., frequency, voltage, and transducer polarity). We characterize devices using techniques such as laser Doppler vibrometry (LDV) and infrared imaging, along with evaluating droplet injection for our series of device designs, constructions, and operating parameters. Although we find that LiNbO3 device designs generate acoustic fields, we demonstrate that droplet injection occurs only due to dielectrophoretic forces. We deduce that droplet injection is caused by the coupled dielectrophoretic forces arising from the operation of elmIDTs rather than by acoustophoretic forces for this specific device design. We arrive at this conclusion because equivalent droplet injection occurs without the presence of an acoustic field using the same electrode designs on nonpiezo active glass substrate devices. This work establishes a methodology to pinpoint the major contributing force of droplet manipulation in droplet-based acoustomicrofluidics.

Acoustofluidic Actuation of Living Cells

Acoutofluidics is an increasingly developing and maturing technical discipline. With the advantages of being label-free, non-contact, bio-friendly, high-resolution, and remote-controllable, it is very suitable for the operation of living cells. After decades of fundamental laboratory research, its technical principles have become increasingly clear, and its manufacturing technology has gradually become popularized. Presently, various imaginative applications continue to emerge and are constantly being improved. Here, we introduce the development of acoustofluidic actuation technology from the perspective of related manipulation applications on living cells. Among them, we focus on the main development directions such as acoustofluidic sorting, acoustofluidic tissue engineering, acoustofluidic microscopy, and acoustofluidic biophysical therapy. This review aims to provide a concise summary of the current state of research and bridge past developments with future directions, offering researchers a comprehensive overview and sparking innovation in the field.

Bipolar Electrode-based Sheath-Less Focusing and Continuous Acoustic Sorting of Particles and Cells in an Integrated Microfluidic Device

Sheath-less focusing and sorting of cells or particles is an important preprocessing step in a variety of biochemical applications. Most of the previous sorting methods depend on the use of sheath flows to realize efficient cell focusing. The sheath flow dilutes the sample and requires precise flow control via additional channels. We, for the first time, reported a method of bipolar electrode (BPE)-based sheath-less focusing, switching, and tilted-angle standing surface acoustic wave-based sorting of cells and particles in continuous flow. The device consists of a piezoelectric substrate with a pair of BPEs for focusing and switching, and a pair of interdigitated transducers for cell sorting. Smaller cells experience a weak acoustic force and reach the lower outlet, whereas larger cells are subjected to a strong acoustic force such that they are propelled toward the upper outlet. We first validate the device functionality by sorting 5 and 8 μm PS beads with a high sorting efficiency. The working and deflection regions were increased by propelling the particle beam toward the bottom edge of BPE via changing the applied voltage of BPE, further improving the sorting performance with high efficiency (94%) and purity (92%). We then conducted a verification for sorting THP-1 and yeast cells, and the efficiency and purity reached 90.7 and 91.5%, respectively. This integrated device eliminates the requirement of balancing the flow of several sheath inlets and provides a robust and unique approach for cell sorting applications, showing immense promise in various applications, such as medical diagnosis, drug delivery, and personalized medicine.

Investigation on submicron particle separation and deflection using tilted-angle standing surface acoustic wave microfluidics

With the development of in vitro diagnostics, extracting submicron scale particles from mixed body fluids samples is crucial. In recent years, microfluidic separation has attracted much attention due to its high efficiency, label-free, and inexpensive nature. Among the microfluidic-based separation, the separation based on ultrasonic standing waves has gradually become a powerful tool. A microfluid environment containing a tilted-angle ultrasonic standing surface acoustic wave (taSSAW) field has been widely adapted and designed to separate submicron particles for biochemical applications. This paper investigated submicron particle defection in microfluidics using taSSAWs analytically. Particles with 0.1-1 μm diameters were analyzed under acoustic pressure, flow rate, tilted angle, and SSAW frequency. According to different acoustic radiation forces acting on the particles, the motion of large-diameter particles was more likely to deflect to the direction of the nodal lines. Decreasing the input flow rate or increasing acoustic pressure and acoustic wave frequency can improve particle deflection. The tilted angle can be optimized by analyzing the simulation results. Based on the simulation analysis, we experimentally showed the separation of polystyrene microspheres (100 nm) from the mixed particles and exosomes (30-150 nm) from human plasma. This research results can provide a certain reference for the practical design of bioparticle separation utilizing acoustofluidic devices.

Exploiting Sound for Emerging Applications of Extracellular Vesicles

Extracellular vesicles are nano- to microscale, membrane-bound particles released by cells into extracellular space, and act as carriers of biomarkers and therapeutics, holding promising potential in translational medicine. However, the challenges remain in handling and detecting extracellular vesicles for disease diagnosis as well as exploring their therapeutic capability for disease treatment. Here, we review the recent engineering and technology advances by leveraging the power of sound waves to address the challenges in diagnostic and therapeutic applications of extracellular vesicles and biomimetic nanovesicles. We first introduce the fundamental principles of sound waves for understanding different acoustic-assisted extracellular vesicle technologies. We discuss the acoustic-assisted diagnostic methods including the purification, manipulation, biosensing, and bioimaging of extracellular vesicles. Then, we summarize the recent advances in acoustically enhanced therapeutics using extracellular vesicles and biomimetic nanovesicles. Finally, we provide perspectives into current challenges and future clinical applications of the promising extracellular vesicles and biomimetic nanovesicles powered by sound.

The effect of microchannel height on the acoustophoretic motion of sub-micron particles

Acoustophoresis is an effective technique for particle manipulation. Acoustic radiation force scales with particle volume, enabling size separation. Yet, isolating sub-micron particles remains a challenge due to the acoustic streaming effect (ASE). While some studies confirmed the focusing ability of ASE, others reported continuous stirring effects. To investigate the parameters that influence ASE-induced particle motion in a microchannel, this study examined the effect of microchannel height and particle size. We employed standing surface acoustic wave (SSAW) to manipulate polystyrene particles suspended in the water-filled microchannel. The results show that ASE can direct particles as small as 0.31 µm in diameter to the centre of the streaming vortices, and increasing the channel height enhances the focusing effect. Smaller particles circulate in the streaming vortices continuously, with no movement towards the centres. We also discovered that when the channel height is at least 0.75 the fluid wavelength, particles transitioning from acoustic radiation-dominated to ASE-dominated share the same equilibrium position, which differs from the pressure nodes and the vortices' centres. The spatial distance between particles in different categories can lead to particle separation. Therefore, ASE is a potential alternative mechanism for sub-micron particle sorting when the channel height is accurately adjusted.

Acoustofluidics - changing paradigm in tissue engineering, therapeutics development, and biosensing

For more than 70 years, acoustic waves have been used to screen, diagnose, and treat patients in hundreds of medical devices. The biocompatible nature of acoustic waves, their non-invasive and contactless operation, and their compatibility with wide visualization techniques are just a few of the many features that lead to the clinical success of sound-powered devices. The development of microelectromechanical systems and fabrication technologies in the past two decades reignited the spark of acoustics in the discovery of unique microscale bio applications. Acoustofluidics, the combination of acoustic waves and fluid mechanics in the nano and micro-realm, allowed researchers to access high-resolution and controllable manipulation and sensing tools for particle separation, isolation and enrichment, patterning of cells and bioparticles, fluid handling, and point of care biosensing strategies. This versatility and attractiveness of acoustofluidics have led to the rapid expansion of platforms and methods, making it also challenging for users to select the best acoustic technology. Depending on the setup, acoustic devices can offer a diverse level of biocompatibility, throughput, versatility, and sensitivity, where each of these considerations can become the design priority based on the application. In this paper, we aim to overview the recent advancements of acoustofluidics in the multifaceted fields of regenerative medicine, therapeutic development, and diagnosis and provide researchers with the necessary information needed to choose the best-suited acoustic technology for their application. Moreover, the effect of acoustofluidic systems on phenotypic behavior of living organisms are investigated. The review starts with a brief explanation of acoustofluidic principles, the different working mechanisms, and the advantages or challenges of commonly used platforms based on the state-of-the-art design features of acoustofluidic technologies. Finally, we present an outlook of potential trends, the areas to be explored, and the challenges that need to be overcome in developing acoustofluidic platforms that can echo the clinical success of conventional ultrasound-based devices.

Rapid prototyping of functional acoustic devices using laser manufacturing

Acoustic patterning of micro-particles has many important biomedical applications. However, fabrication of such microdevices is costly and labor-intensive. Among conventional fabrication methods, photo-lithography provides high resolution but is expensive and time consuming, and not ideal for rapid prototyping and testing for academic applications. In this work, we demonstrate a highly efficient method for rapid prototyping of acoustic patterning devices using laser manufacturing. With this method we can fabricate a newly designed functional acoustic device in 4 hours. The acoustic devices fabricated using this method can achieve sub-wavelength, complex and non-periodic patterning of microparticles and biological objects with a spatial resolution of 60 μm across a large active manipulation area of 10 × 10 mm2.

Fabrication and Manipulation of Non-Spherical Particles in Microfluidic Channels: A Review

Non-spherical shape is a general appearance feature for bioparticles. Therefore, a mechanical mechanism study of non-spherical particle migration in a microfluidic chip is essential for more precise isolation of target particles. With the manipulation of non-spherical particles, refined disease detection or medical intervention for human beings will be achievable in the future. In this review, fabrication and manipulation of non-spherical particles are discussed. Firstly, various fabrication methods for non-spherical microparticle are introduced. Then, the active and passive manipulation techniques for non-spherical particles are briefly reviewed, including straight inertial microchannels, secondary flow inertial microchannels and deterministic lateral displacement microchannels with extremely high resolution. Finally, applications of viscoelastic flow are presented which obviously increase the precision of non-spherical particle separation. Although various techniques have been employed to improve the performance of non-spherical particle manipulation, the universal mechanism behind this has not been fully discussed. The aim of this review is to provide a reference for non-spherical particle manipulation study researchers in every detail and inspire thoughts for non-spherical particle focused device design.

Recent advances in acoustofluidic separation technology in biology

Acoustofluidic separation of cells and particles is an emerging technology that integrates acoustics and microfluidics. In the last decade, this technology has attracted significant attention due to its biocompatible, contactless, and label-free nature. It has been widely validated in the separation of cells and submicron bioparticles and shows great potential in different biological and biomedical applications. This review first introduces the theories and mechanisms of acoustofluidic separation. Then, various applications of this technology in the separation of biological particles such as cells, viruses, biomolecules, and exosomes are summarized. Finally, we discuss the challenges and future prospects of this field.

Novel Markers for Liquid Biopsies in Cancer Management: Circulating Platelets and Extracellular Vesicles

Although radiologic imaging and histologic assessment of tumor tissues are classic approaches for diagnosis and monitoring of treatment response, they have many limitations. These include challenges in distinguishing benign from malignant masses, difficult access to the tumor, high cost of the procedures, and tumor heterogeneity. In this setting, liquid biopsy has emerged as a potential alternative for both diagnostic and monitoring purposes. The approaches to liquid biopsy include cell-free DNA/circulating tumor DNA, long and micro noncoding RNAs, proteins/peptides, carbohydrates/lectins, lipids, and metabolites. Other approaches include detection and analysis of circulating tumor cells, extracellular vesicles, and tumor-activated platelets. Ultimately, reliable use of liquid biopsies requires bioinformatics and statistical integration of multiple datasets to achieve approval in a Clinical Laboratory Improvement Amendments setting. This review provides a balanced and critical assessment of recent discoveries regarding tumor-derived biomarkers in liquid biopsies along with the potential and pitfalls for cancer detection and longitudinal monitoring.

Advances and enabling technologies for phase-specific cell cycle synchronisation

Cell cycle synchronisation is the process of isolating cell populations at specific phases of the cell cycle from heterogeneous, asynchronous cell cultures. The process has important implications in targeted gene-editing and drug efficacy of cells and in studying cell cycle events and regulatory mechanisms involved in the cell cycle progression of multiple cell species. Ideally, cell cycle synchrony techniques should be applicable for all cell types, maintain synchrony across multiple cell cycle events, maintain cell viability and be robust against metabolic and physiological perturbations. In this review, we categorize cell cycle synchronisation approaches and discuss their operational principles and performance efficiencies. We highlight the advances and technological development trends from conventional methods to the more recent microfluidics-based systems. Furthermore, we discuss the opportunities and challenges for implementing high throughput cell synchronisation and provide future perspectives on synchronisation platforms, specifically hybrid cell synchrony modalities, to allow the highest level of phase-specific synchrony possible with minimal alterations in diverse types of cell cultures.

Acoustic Biosensors and Microfluidic Devices in the Decennium: Principles and Applications

Lab-on-a-chip (LOC) technology has gained primary attention in the past decade, where label-free biosensors and microfluidic actuation platforms are integrated to realize such LOC devices. Among the multitude of technologies that enables the successful integration of these two features, the piezoelectric acoustic wave method is best suited for handling biological samples due to biocompatibility, label-free and non-invasive properties. In this review paper, we present a study on the use of acoustic waves generated by piezoelectric materials in the area of label-free biosensors and microfluidic actuation towards the realization of LOC and POC devices. The categorization of acoustic wave technology into the bulk acoustic wave and surface acoustic wave has been considered with the inclusion of biological sample sensing and manipulation applications. This paper presents an approach with a comprehensive study on the fundamental operating principles of acoustic waves in biosensing and microfluidic actuation, acoustic wave modes suitable for sensing and actuation, piezoelectric materials used for acoustic wave generation, fabrication methods, and challenges in the use of acoustic wave modes in biosensing. Recent developments in the past decade, in various sensing potentialities of acoustic waves in a myriad of applications, including sensing of proteins, disease biomarkers, DNA, pathogenic microorganisms, acoustofluidic manipulation, and the sorting of biological samples such as cells, have been given primary focus. An insight into the future perspectives of real-time, label-free, and portable LOC devices utilizing acoustic waves is also presented. The developments in the field of thin-film piezoelectric materials, with the possibility of integrating sensing and actuation on a single platform utilizing the reversible property of smart piezoelectric materials, provide a step forward in the realization of monolithic integrated LOC and POC devices. Finally, the present paper highlights the key benefits and challenges in terms of commercialization, in the field of acoustic wave-based biosensors and actuation platforms.

Reduced acoustic resonator dimensions improve focusing efficiency of bacteria and submicron particles

In this study, we demonstrate an acoustofluidic device that enables single-file focusing of submicron particles and bacteria using a two-dimensional (2D) acoustic standing wave. The device consists of a 100 μm × 100 μm square channel that supports 2D particle focusing in the channel center at an actuation frequency of 7.39 MHz. This higher actuation frequency compared with conventional bulk acoustic systems enables radiation-force-dominant motion of submicron particles and overcomes the classical size limitation (≈2 μm) of acoustic focusing. We present acoustic radiation force-based focusing of particles with diameters less than 0.5 μm at a flow rate of 12 μL min^-1, and 1.33 μm particles at flow rates up to 80 μL min^-1. The device focused 0.25 μm particles by the 2D acoustic radiation force while undergoing a channel cross-section centered, single-vortex acoustic streaming. A suspension of bacteria was also investigated to evaluate the biological relevance of the device, which demonstrated the alignment of bacteria in the channel at a flow rate of up to 20 μL min^-1. The developed acoustofluidic device can align submicron particles within a narrow flow stream in a highly robust manner, validating its use as a flow-through focusing chamber to perform high-throughput and accurate flow cytometry of submicron objects.

Influences of microparticle radius and microchannel height on SSAW-based acoustophoretic aggregation

The use of acoustic waves for microfluidic aggregation has become widespread in chemistry, biology and medicine. Although numerous experimental and analytical studies have been undertaken to study the acoustophoretic aggregation mechanisms, few studies have been conducted to optimise the device design. This paper presents a numerical investigation of the acoustophoresis of microparticles suspended in compressible liquid. The wall of the rectangular microchannel is made of Polydimethylsiloxane (PDMS), and Standing Surface Acoustic Waves (SSAW) are introduced into the channel from the bottom wall. First, the relative amplitude of the acoustic radiation force and the viscous drag force is evaluated for particles of different radii ranging from 0.1μm to 15μm. Only when the particle size is larger than a critical value can the particles accumulate at acoustic pressure nodes (PNs). The efficiency of the particle accumulation depends on the microchannel height, so an extensive parametric study is then undertaken to identify the optimum microchannel height. The optimum height, when normalised by the acoustic wavelength, is found to be between 0.57 and 0.82. These findings provide insights into the design of acoustophoretic devices.

Surface acoustic wave (SAW) techniques in tissue engineering

Recently, the introduction of surface acoustic wave (SAW) technique for microfluidics has drawn a lot of attention. The pattern and mutual communication in cell layers, tissues, and organs play a critical role in tissue homeostasis and regeneration and may contribute to disease occurrence and progression. Tissue engineering aims to repair and regenerate damaged organs, depending on biomimetic scaffolds and advanced fabrication technology. However, traditional bioengineering synthesis approaches are time-consuming, heterogeneous, and unmanageable. It is hard to pattern cells in scaffolds effectively with no impact on cell viability and function. Here, we summarize a biocompatible, easily available, label-free, and non-invasive tool, surface acoustic wave (SAW) technique, which is getting a lot of attention in tissue engineering. SAW technique can realize accurate sorting, manipulation, and cells' pattern and rapid formation of spheroids. By integrating several SAW devices onto lab-on-a-chip platforms, tissue engineering lab-on-a-chip system was proposed. To the best of our knowledge, this is the first report to summarize the application of this novel technique in the field of tissue engineering.

Leukapheresis and Hyperleukocytosis, Past and Future

Hyperleukocytosis is a hematologic crisis caused by excessive proliferation of leukemic cells and has a relatively high early mortality due to a series of severe complications. Therefore, prompt and effective intervention is required. Leukapheresis performed using apheresis equipment to separate leukocytes from peripheral blood, at the same time returns autologous plasma, platelets and erythrocytes to the patient, is applied clinically for the treatment of hyperleukocytosis. Leukapheresis not only removes excessive leukocytes rapidly and corrects metabolic abnormalities but also alleviates the symptoms of leukostasis. In addition, the procedure of leukapheresis is generally well tolerated. Leukapheresis has become one of the most imperative adjuvant therapies to treat hyperleukocytosis, especially in the patient who was not inappropriate to cytoreduce with Ara-C or hydroxyurea. In this review, we present the background of leukapheresis development and highlight its clinical application in hyperleukocytic leukemia patients.

High-Throughput Cell Concentration Using A Piezoelectric Pump in Closed-Loop Viscoelastic Microfluidics

Cell concentration is a critical process in biological assays and clinical diagnostics for the pre-treatment of extremely rare disease-related cells. The conventional technique for sample preconcentration and centrifugation has the limitations of a batch process requiring expensive and large equipment. Therefore, a high-throughput continuous cell concentration technique needs to be developed. However, in single-pass operation, the required concentration ratio is hard to achieve. In this study, we propose a closed-loop continuous cell concentration system using a viscoelastic non-Newtonian fluid. For miniaturized and integrated systems, two piezoelectric pumps were adopted. The pumping capability generated by a piezoelectric pump in a microfluidic channel was evaluated depending on the applied voltage, frequency, sample viscosity, and channel length. The concentration performance of the device was evaluated using 13 μm particles and white blood cells (WBCs) with different channel lengths and voltages. In the closed-loop system, the focused cells collected at the center outlet were sent back to the inlet, while the buffer solution was removed to the side outlets. Finally, to expand the clinical applicability of our closed-loop system, WBCs in lysed blood samples with 70% hematocrit and prostate cancer cells in urine samples were used. Using the closed-loop system, WBCs were concentrated by ~63.4 ± 0.8-fold within 20 min to a final volume of 160 μL using 10 mL of lysed blood sample with 70% hematocrit (~3 cP). In addition, prostate cancer cells in 10 mL urine samples were concentrated by ~64.1-fold within ~11 min due to low viscosity (~1 cP).

Microliter ultrafast centrifuge platform for size-based particle and cell separation and extraction using novel omnidirectional spiral surface acoustic waves

Asymmetric surface acoustic waves have been shown useful in separating particles and cells in many microfluidics designs, mostly notably sessile microdroplets. However, no one has successfully extracted target particles or cells for later use from such samples. We present a novel omnidirectional spiral surface acoustic wave (OSSAW) design that exploits a new cut of lithium niobate, 152 Y-rotated, to rapidly rotate a microliter sessile drop to ∼10 g, producing efficient multi-size particle separation. We further extract the separated particles for the first time, demonstrating the ability to target specific particles, for example, platelets from mouse blood for further integrated point-of-care diagnostics. Within ∼5 s of surface acoustic wave actuation, particles with diameter of 5 μm and 1 μm can be separated into two portions with a purity of 83% and 97%, respectively. Red blood cells and platelets within mouse blood are further demonstrated to be separated with a purity of 93% and 84%, respectively. These advancements potentially provide an effective platform for whole blood separation and point-of-care diagnostics without need for micro or nanoscale fluidic enclosures.

Microparticle manipulation using laser-induced thermophoresis and thermal convection flow

We demonstrate manipulation of microbeads with diameters from 1.5 to 10 µm and Jurkat cells within a thin fluidic device using the combined effect of thermophoresis and thermal convection. The heat flow is induced by localized absorption of laser light by a cluster of single walled carbon nanotubes, with no requirement for a treated substrate. Characterization of the system shows the speed of particle motion increases with optical power absorption and is also affected by particle size and corresponding particle suspension height within the fluid. Further analysis shows that the thermophoretic mobility (DT) is thermophobic in sign and increases linearly with particle diameter, reaching a value of 8 µm2 s-1 K-1 for a 10 µm polystyrene bead.

Submicron Particle and Cell Concentration in a Closed Chamber Surface Acoustic Wave Microcentrifuge

Preconcentrating particulate and cellular matter for their isolation or detection is often a necessary and critical sample preparation or purification step in many lab-on-a-chip diagnostic devices. While surface acoustic wave (SAW) microcentrifugation has been demonstrated as a powerful means to drive efficient particle concentration, this has primarily been limited to micron dimension particles. When the particle size is around 1 μm or below, studies on SAW microcentrifugation to date have shown that particle ring-like aggregates can only be obtained in contrast to the localized concentrated clusters that are obtained with larger particles. Considering the importance of submicron particles and bioparticles that are common in many real-world samples, we elucidate why previous studies have not been able to achieve the concentration of these smaller particles to completion, and we present a practical solution involving a novel closed chamber configuration that minimizes sample heating and eliminates evaporation to show that it is indeed possible to drive submicron particle and cell concentration down to 200 nm diameters with SAW microcentrifugation over longer durations.

In situ generation of plasma-activated aerosols via surface acoustic wave nebulization for portable spray-based surface bacterial inactivation

The presence of reactive species in plasma-activated water is known to induce oxidative stresses in bacterial species, which can result in their inactivation. By integrating a microfludic chipscale nebulizer driven by surface acoustic waves (SAWs) with a low-temperature atmospheric plasma source, we demonstrate an efficient technique for in situ production and application of plasma-activated aerosols for surface disinfection. Unlike bulk conventional systems wherein the water is separately batch-treated within a container, we show in this work the first demonstration of continuous plasma-treatment of water as it is transported through a paper strip from a reservoir onto the chipscale SAW device. The significantly larger surface area to volume ratio of the water within the paper strip leads to a significant reduction in the duration of the plasma-treatment, while maintaining the concentration of the reactive species. The subsequent nebulization of the plasma-activated water by the SAW then allows the generation of plasma-activated aerosols, which can be directly sprayed onto the contaminated surface, therefore eliminating the storage of the plasma-activated water and hence circumventing the typical limitation in conventional systems wherein the concentration of the reactive species diminishes over time during storage, resulting in a reduction in the efficacy of bacterial inactivation. In particular, we show up to 96% reduction in Escherichia coli colonies through direct spraying with the plasma-activated aerosols. This novel, low-cost, portable and energy-efficient hybrid system necessitates only minimal maintenance as it only requires the supply of tap water and battery power for operation, and is thus suitable for decontamination in home environments.

Detection of Rare Objects by Flow Cytometry: Imaging, Cell Sorting, and Deep Learning Approaches

Flow cytometry nowadays is among the main working instruments in modern biology paving the way for clinics to provide early, quick, and reliable diagnostics of many blood-related diseases. The major problem for clinical applications is the detection of rare pathogenic objects in patient blood. These objects can be circulating tumor cells, very rare during the early stages of cancer development, various microorganisms and parasites in the blood during acute blood infections. All of these rare diagnostic objects can be detected and identified very rapidly to save a patient's life. This review outlines the main techniques of visualization of rare objects in the blood flow, methods for extraction of such objects from the blood flow for further investigations and new approaches to identify the objects automatically with the modern deep learning methods.

Fully automated platelet isolation on a centrifugal microfluidic device for molecular diagnostics

Platelets play crucial roles in hemostasis and immunity. Over the last decades, clinical evidence has revealed the significance of platelets as complementary biomarkers for the detection and treatment of various diseases, including cancer. Due to a lack of well standardized convenient isolation methods for platelets, pre-analytical factors such as complex handling procedures negatively impact the quality of the platelet samples, including overactivation, low purity, and poor reproducibility. This may lead to biased interpretation of various downstream analyses, such as proteomic and genomic analyses. Herein, we describe a fully automated lab-on-a-disc-based method of platelet isolation from a small volume of blood (<1 mL). This method provides higher yields (>4 folds) and purity (>99%) and lower platelet activation than the conventional method. Moreover, it was also superior in the detection of platelet-related RNAs CD41, PF4, and P2Y12 due to lower contamination with white blood cells.

Enhancing greywater treatment via MHz-Order surface acoustic waves

There is a pressing need for efficient biological treatment systems for the removal of organic compounds in greywater given the rapid increase in household wastewater produced as a consequence of rapid urbanisation. Moreover, proper treatment of greywater allows its reuse that can significantly reduce the demand for freshwater supplies. Herein, we demonstrate the possibility of enhancing the removal efficiency of solid contaminants from greywater using MHz-order surface acoustic waves (SAWs). A key distinction of the use of these high frequency surface acoustic waves, compared to previous work on its lower frequency (kHz order) bulk ultrasound counterpart for wastewater treatment, is the absence of cavitation, which can inflict considerable damage on bacteria, thus limiting the intensity and duration, and hence the efficiency enhancement, associated with the acoustic exposure. In particular, we show that up to fivefold improvement in the removal efficiency can be obtained, primarily due to the ability of the acoustic pressure field in homogenizing and reducing the size of bacterial clusters in the sample, therefore providing a larger surface area that promotes greater bacteria digestion. Alternatively, the SAW exposure allows the reduction in the treatment duration to achieve a given level of removal efficiency, thus facilitating higher treatment rates and hence processing throughput. Given the low-cost of the miniature chipscale platform, these promising results highlight its possibility for portable greywater treatment for domestic use or for large-scale industrial wastewater processing through massive parallelization.

Platelet-Rich Plasma as a Treatment for Androgenetic Alopecia

BACKGROUND

Platelet-rich plasma (PRP) treatment may encourage hair growth by promoting cellular maturation, differentiation, and proliferation.

OBJECTIVE

The objective of this study was to evaluate the effectiveness of PRP as a treatment for androgenetic alopecia (AGA).

MATERIALS AND METHODS

A literature search combined with meta-analysis was used to calculate the overall standardized mean difference (SMD) in hair density in patients treated with PRP injections in comparison with baseline and placebo treatment. Chi squared analysis and Fisher exact test were used to investigate variation in protocols.

RESULTS

The overall SMD in hair density was 0.58 (95% confidence interval [CI]: 0.35-0.80) and 0.51 (95% CI: 0.23-0.80, p < .0004) in favor of PRP treatment when compared with baseline and placebo treatment, respectively.

CONCLUSION

Platelet-rich plasma is beneficial in the treatment of AGA. It is recommended that 3 monthly sessions of PRP (once monthly ×3 treatments) be used followed by a 3- to 6-month maintenance period.

Acoustic mixing in a dome-shaped chamber-based SAW (DC-SAW) device

The use of an open droplet system for surface acoustic wave (SAW)-based applications has been limited by droplet instability at high input power. This study introduces a dome-shaped chamber-based SAW (DC-SAW) device for the first time, which can be fabricated simply using a single adhesive tape and a drop of ultraviolet-curable material without soft lithography processes. The dome-shaped chamber device with a contact angle of 68° enables the maximizing of the effect of SAW transmitted at a refraction angle of roughly 22°, negating the droplet instability. The DC-SAW device was applied to acoustic mixing to estimate its capability. Acoustic mixing of two different fluids (i.e., deionized water and fluorescent particle suspension) was demonstrated in the dome-shaped chamber device. Moreover, the effect of flow rate and applied voltage on mixing performance was estimated. With the decreasing flow rate and increasing applied voltage, mixing performance was enhanced. At an applied voltage of 20 V, mixing indices were higher than 0.9 at a total flow rate of 300 μl min^-1.

Blood platelet enrichment in mass-producible surface acoustic wave (SAW) driven microfluidic chips

The ability to separate specific biological components from cell suspensions is indispensable for liquid biopsies, and for personalized diagnostics and therapy. This paper describes an advanced surface acoustic wave (SAW) based device designed for the enrichment of platelets (PLTs) from a dispersion of PLTs and red blood cells (RBCs) at whole blood concentrations, opening new possibilities for diverse applications involving cell manipulation with high throughput. The device is made of patterned SU-8 photoresist that is lithographically defined on the wafer scale with a new proposed methodology. The blood cells are initially focused and subsequently separated by an acoustic radiation force (ARF) applied through standing SAWs (SSAWs). By means of flow cytometric analysis, the PLT concentration factor was found to be 7.7, and it was proven that the PLTs maintain their initial state. A substantially higher cell throughput and considerably lower applied powers than comparable devices from literature were achieved. In addition, fully coupled 3D numerical simulations based on SAW wave field measurements were carried out to anticipate the coupling of the wave field into the fluid, and to obtain the resulting pressure field. A comparison to the acoustically simpler case of PDMS channel walls is given. The simulated results show an ideal match to the experimental observations and offer the first insights into the acoustic behavior of SU-8 as channel wall material. The proposed device is compatible with current (Lab-on-a-Chip) microfabrication techniques allowing for mass-scale, reproducible chip manufacturing which is crucial to push the technology from lab-based to real-world applications.

Sheathless Shape-Based Separation of Candida Albicans Using a Viscoelastic Non-Newtonian Fluid

Rapid and accurate identification of Candida albicans from among other candida species is critical for cost-effective treatment and antifungal drug assays. Shape is a critical biomarker indicating cell type, cell cycle, and environmental conditions; however, most microfluidic techniques have been focused only on size-based particle/cell manipulation. This study demonstrates a sheathless shape-based separation of particles/cells using a viscoelastic non-Newtonian fluid. The size of C. albicans was measured at 37 °C depending on the incubation time (0 h, 1 h, and 2 h). The effects of flow rates on the flow patterns of candida cells with different shapes were examined. Finally, 2-h-incubated candida cells with germ tube formations (≥26 μm) were separated from spherical candida cells and shorter candida cells with a separation efficiency of 80.9% and a purity of 91.2% at 50 μL/min.

Acoustofluidic separation of cells and particles

Acoustofluidics, the integration of acoustics and microfluidics, is a rapidly growing research field that is addressing challenges in biology, medicine, chemistry, engineering, and physics. In particular, acoustofluidic separation of biological targets from complex fluids has proven to be a powerful tool due to the label-free, biocompatible, and contact-free nature of the technology. By carefully designing and tuning the applied acoustic field, cells and other bioparticles can be isolated with high yield, purity, and biocompatibility. Recent advances in acoustofluidics, such as the development of automated, point-of-care devices for isolating sub-micron bioparticles, address many of the limitations of conventional separation tools. More importantly, advances in the research lab are quickly being adopted to solve clinical problems. In this review article, we discuss working principles of acoustofluidic separation, compare different approaches of acoustofluidic separation, and provide a synopsis of how it is being applied in both traditional applications, such as blood component separation, cell washing, and fluorescence activated cell sorting, as well as emerging applications, including circulating tumor cell and exosome isolation.

Separating extracellular vesicles and lipoproteins via acoustofluidics

Extracellular vesicles (EVs) and lipoproteins are abundant and co-exist in blood. Both have been proven to be valuable as diagnostic biomarkers and for therapeutics. However, EVs and lipoproteins are both on the submicron scale and overlap in size distributions. Conventional methods to separate EVs and lipoproteins are inefficient and time-consuming. Here we present an acoustofluidic-based separation technique that is based on the acoustic property differences of EVs and lipoproteins. By using the acoustofluidic technology, EVs and subgroups of lipoproteins are separated in a label-free, contact-free, and continuous manner. With its ability for simple, rapid, efficient, continuous-flow isolation, our acoustofluidic technology could be a valuable tool for health monitoring, disease diagnosis, and personalized medicine.

Label-free detection of pepsinogen 1 and 2 by polyethylene coating Lamb microfluidic device

Early screening of gastric cancer is a critical importance for the improvement of patients' survival rate. Here, a polyethylene coating Lamb (PE-Lamb) microfluidic device with immune layer for gastric cancer label-free detection was constructed. Two serum pepsinogen 1 (PG1) and pepsinogen 2 (PG2) biomarkers were applied to screen and predict the appearance of gastric cancer. Compared with enzyme-linked immunosorbent assay (ELISA), this method achieved a higher sensitivity and less time (40 min vs 120 min). The limit of detections (LOD) were reached 60 pg/mL for PG1 and 30 pg/mL for PG2, which have two orders of magnitude lower than traditional ELISA. The linearity coefficient indexes (R²) for PG1 and PG2 were 0.992 and 0.953 respectively, which is similar to that of ELISA. In addition, PG1 and PG2 mixed antigens sample with human serum was detected by PE-Lamb approach, and the frequency response showed high reproducibility and specificity. The results indicate that PE-lamb diagnostic technique is a novel and promising method for high-throughput screening and early diagnosis of gastric cancer.

Viscoelastic Separation and Concentration of Fungi from Blood for Highly Sensitive Molecular Diagnostics

Isolation and concentration of fungi in the blood improves sensitivity of the polymerase chain reaction (PCR) method to detect fungi in blood. This study demonstrates a sheathless, continuous separation and concentration method of candida cells using a viscoelastic fluid that enables rapid detection of rare candida cells by PCR analysis. To validate device performance using a viscoelastic fluid, flow characteristics of 2 μm particles were estimated at different flow rates. Additionally, a mixture of 2 μm and 13 μm particles was successfully separated based on size difference at 100 μl/min. Candida cells were successfully separated from the white blood cells (WBCs) with a separation efficiency of 99.1% and concentrated approximately 9.9-fold at the center outlet compared to the initial concentration (~2.5 × 10⁷ cells/ml). Sequential 1st and 2nd concentration processes were used to increase the final number of candida cells to ~2.3 × 10⁹ cells/ml, which was concentrated ~92-fold. Finally, despite the undetectable initial concentration of 10¹ CFU/ml, removal of WBCs and the additional buffer solution enabled the quantitative reverse transcription (RT)-PCR detection of candida cells after the 1st concentration (Ct = 31.43) and the 2nd concentration process (Ct = 29.30).

Plastic-based acoustofluidic devices for high-throughput, biocompatible platelet separation

Platelet separation is a crucial step for both blood donation and treatment of essential thrombocytosis. Here we present an acoustofluidic device that is capable of performing high-throughput, biocompatible platelet separation using sound waves. The device is entirely made of plastic material, which renders the device disposable and more suitable for clinical use. We used this device to process undiluted human whole blood, and we demonstrate a sample throughput of 20 mL min-1, a platelet recovery rate of 87.3%, and a red/white blood cell removal rate of 88.9%. We preserved better platelet function and integrity for isolated platelets than those which are isolated using established methods. Our device features advantages such as rapid fabrication, high throughput, and biocompatibility, so it is a promising alternative to existing platelet separation approaches.

Applications of Acoustofluidics in Bioanalytical Chemistry

Acoustics has a broad spectrum of applications, ranging from noise cancelation to ultrasonic imaging. In the past decade, there has been increasing interest in developing acoustic-based methods for biological and biomedical applications. This Perspective summarizes the recent progress in applying acoustofluidic methods (i.e., the fusion of acoustics and microfluidics) to bioanalytical chemistry. We describe the concepts of acoustofluidics and how it can be tailored to different types of bioanalytical applications, including sample concentration, fluorescence-activated cell sorting, label-free cell/particle separation, and fluid manipulation. Examples of each application are given, and the benefits and limitations of these methods are discussed. Finally, our perspectives on the directions that developing solutions should take to address the bottlenecks in the acoustofluidic applications in bioanalytical chemistry are presented.

A review of sorting, separation and isolation of cells and microbeads for biomedical applications: microfluidic approaches

We have reviewed the microfluidic approaches for cell/particle isolation and sorting, and extensively explained the mechanism behind each method.

Developments in label-free microfluidic methods for single-cell analysis and sorting

Advancements in microfluidic technologies have led to the development of many new tools for both the characterization and sorting of single cells without the need for exogenous labels. Label-free microfluidics reduce the preparation time, reagents needed, and cost of conventional methods based on fluorescent or magnetic labels. Furthermore, these devices enable analysis of cell properties such as mechanical phenotype and dielectric parameters that cannot be characterized with traditional labels. Some of the most promising technologies for current and future development toward label-free, single-cell analysis and sorting include electronic sensors such as Coulter counters and electrical impedance cytometry; deformation analysis using optical traps and deformation cytometry; hydrodynamic sorting such as deterministic lateral displacement, inertial focusing, and microvortex trapping; and acoustic sorting using traveling or standing surface acoustic waves. These label-free microfluidic methods have been used to screen, sort, and analyze cells for a wide range of biomedical and clinical applications, including cell cycle monitoring, rapid complete blood counts, cancer diagnosis, metastatic progression monitoring, HIV and parasite detection, circulating tumor cell isolation, and point-of-care diagnostics. Because of the versatility of label-free methods for characterization and sorting, the low-cost nature of microfluidics, and the rapid prototyping capabilities of modern microfabrication, we expect this class of technology to continue to be an area of high research interest going forward. New developments in this field will contribute to the ongoing paradigm shift in cell analysis and sorting technologies toward label-free microfluidic devices, enabling new capabilities in biomedical research tools as well as clinical diagnostics. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > Diagnostic Nanodevices.

Acoustically-mediated intracellular delivery

Recent breakthroughs in gene editing have necessitated practical ex vivo methods to rapidly and efficiently re-engineer patient-harvested cells. Many physical membrane-disruption or pore-forming techniques for intracellular delivery, however, result in poor cell viability, while most carrier-mediated techniques suffer from suboptimal endosomal escape and hence cytoplasmic or nuclear targeting. In this work, we show that short exposure of cells to high frequency (>10 MHz) acoustic excitation facilitates temporal reorganisation of the lipid structure in the cell membrane that enhances translocation of gold nanoparticles and therapeutic molecules into the cell within just ten minutes. Due to its transient nature, rapid cell self-healing is observed, leading to high cellular viabilities (>97%). Moreover, the internalised cargo appears to be uniformly distributed throughout the cytosol, circumventing the need for strategies to facilitate endosomal escape. In the case of siRNA delivery, the method is seen to enhance gene silencing by over twofold, demonstrating its potential for enhancing therapeutic delivery into cells.