Power-controlled acoustofluidic manipulation of microparticles.

Recently, surface acoustic wave (SAW) based acoustofluidic separation of microparticles and cells has attracted increasing interest due to accuracy and biocompatibility. Precise control of the input power of acoustofluidic devices is essential for generating optimum acoustic radiation force to manipulate microparticles given their various parameters including size, density, compressibility, and moving velocity. In this work, an acoustophoretic system is developed by employing SAW based interdigital electrode devices. Power meters are applied to closely monitor the incident and reflected powers of the SAW device, which are associated with the separation efficiency. There exists a range of input powers to migrate the microparticles to the pressure node due to their random locations when entering the SAW field. Theoretical analysis is performed to predict a proper input power to separate mixtures of polystyrene microspheres, and the end lateral position of microspheres being acoustically separated. The separation efficiency of four sizes of microspheres, including 20 µm, 15 µm, 10 µm, and 5 µm, is calculated and compared with experimental results, which suggest the input power for separating the mixture of these microspheres. The study provides a practical guidance on operating SAW devices for bioparticle separation using the incident power as a control parameter.

Dual-Wave Acoustofluidic Centrifuge for Ultrafast Concentration of Nanoparticles and Extracellular Vesicles.

Extracellular vesicles (EVs) are secreted nanostructures that play various roles in critical cancer processes. They operate as an intercellular communication system, transferring complex sets of biomolecules from cell to cell. The concentration of EVs is difficult to decipher, and there is an unmet technological need for improved (faster, simpler, and gentler) approaches to isolate EVs from complex matrices. Herein, an acoustofluidic concentration of extracellular vesicles (ACEV) is presented, based on a thin-film printed circuit board with interdigital electrodes mounted on a piezoelectric substrate. An angle of 120° is identified between the electrodes and the reference flat of the piezoelectric substrate for simultaneous generation of Rayleigh and shear horizontal waves. The dual waves create a complex acoustic field in a droplet, resulting in effective concentration of nanoparticles and EVs. The ACEV is able to concentrate 20 nm nanospheres within 105 s and four EV dilutions derived from the human prostate cancer (Du145) cell line in approximately 30 s. Cryo-electron microscopy confirmed the preservation of EV integrity. The ACEV device holds great potential to revolutionize investigations of EVs. Its faster, simpler, and gentler approach to EV isolation and concentration can save time and effort in phenotypic and functional studies of EVs.

Acoustically accelerated neural differentiation of human embryonic stem cells.

Human embryonic stem cells (hESCs) and their derived products offer great promise for targeted therapies and drug screening, however, the hESC differentiation process of mature neurons is a lengthy process. To accelerate the neuron production, an acoustic stimulator producing surface acoustic waves (SAWs) is proposed and realized by clamping a flexible printed circuit board (PCB) directly onto a piezoelectric substrate. Neural differentiation of the hESCs is greatly accelerated after application of the acoustic stimulations. Acceleration mechanisms for neural differentiation have been explored by bulk RNA sequencing, quantitative polymerase chain reaction (qPCR) and immunostaining. The RNA sequencing results show changes of extracellular matrix-related and physiological activity-related gene expression in the low or medium SAW dose group and the high SAW dose group, respectively. The neural progenitor cell markers, including Pax6, Sox1, Sox2, Sox10 and Nkx2-1, are less expressed in the SAW dose groups compared with the control group by the qPCR. Other genes including Alk, Cenpf, Pcdh17, and Actn3 are also found to be regulated by the acoustic stimulation. Moreover, the immunostaining confirmed that more mature neuron marker Tuj1-positive cells, while less stem cell marker Sox2-positive cells, are presented in the SAW dose groups. These results indicate that the SAW stimulation accelerated neural differentiation process. The acoustic stimulator fabricated by using the PCB is a promising tool in regulation of stem cell differentiation process applied in cell therapy. STATEMENT OF SIGNIFICANCE: Human embryonic stem cells (hESC) are used for investigating the complex mechanisms involved in the development of specialized biological cells and organs. Different types of hESCs derived cell products can be used for cell therapy procedures aiming to regenerate functional tissues in patients who suffer from various degenerative diseases. Accelerating the hESCs' differentiation process can considerably benefit the clinical utilization of these cells. This study develops a highly effective acoustic stimulator working at ∼20 MHz to investigate what roles do acousto-mechanical stimuli play in the differentiation of hESCs. Our results show that acoustic dose alters the extracellular matrix and physiological activity-related gene expression, which indicates that the acoustic stimulation is an important tool for regulating the stem cells' differentiation processes in cell therapy.

Correction: Development and characterisation of acoustofluidic devices using detachable electrodes made from PCB.

Correction for 'Development and characterisation of acoustofluidic devices using detachable electrodes made from PCB' by Roman Mikhaylov et al., Lab Chip, 2020, 20, 1807-1814, DOI: 10.1039/C9LC01192G.

Thin film Gallium nitride (GaN) based acoustofluidic Tweezer: Modelling and microparticle manipulation.

Gallium nitride (GaN) is a compound semiconductor which shows advantages in new functionalities and applications due to its piezoelectric, optoelectronic, and piezo-resistive properties. This study develops a thin film GaN-based acoustic tweezer (GaNAT) using surface acoustic waves (SAWs) and demonstrates its acoustofluidic ability to pattern and manipulate microparticles. Although the piezoelectric performance of the GaNAT is compromised compared with conventional lithium niobate-based SAW devices, the inherited properties of GaN allow higher input powers and superior thermal stability. This study shows for the first time that thin film GaN is suitable for the fabrication of the acoustofluidic devices to manipulate microparticles with excellent performance. Numerical modelling of the acoustic pressure fields and the trajectories of mixtures of microparticles driven by the GaNAT was performed and the results were verified from the experimental studies using samples of polystyrene microspheres. The work has proved the robustness of thin film GaN as a candidate material to develop high-power acoustic tweezers, with the potential of monolithical integration with electronics to offer diverse microsystem applications.

Development and characterisation of acoustofluidic devices using detachable electrodes made from PCB.

Acoustofluidics has been increasingly applied in biology, medicine and chemistry due to its versatility in manipulating fluids, cells and nano-/micro-particles. In this paper, we develop a novel and simple technology to fabricate a surface acoustic wave (SAW)-based acoustofluidic device by clamping electrodes made using a printed circuit board (PCB) with a piezoelectric substrate. The PCB-based SAW (PCB-SAW) device is systematically characterised and benchmarked with a SAW device made using the conventional photolithography process with the same specifications. Microparticle manipulations such as streaming in droplets and patterning in microchannels were demonstrated in the PCB-SAW device. In addition, the PCB-SAW device was applied as an acoustic tweezer to pattern lung cancer cells to form three or four traces inside the microchannel in a controllable manner. Cell viability of ∼97% was achieved after acoustic manipulation using the PCB-SAW device, which proved its ability as a suitable tool for acoustophoretic applications.