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Apnoea, a major sleep disorder, affects many adults and causes several issues, such as fatigue, high blood pressure, liver conditions, increased risk of type II diabetes, and heart problems. Therefore, advanced monitoring and diagnosing tools of apnoea disorders are needed to facilitate better treatment, with advantages such as accuracy, comfort of use, cost effectiveness, and embedded computation capabilities to recognise, store, process, and transmit time series data. In this work we present an adaptation of our apnoea-Pi open-source surface acoustic wave (SAW) platform (Apnoea-Pi) to monitor and recognise apnoea in patients. The platform is based on a thin-film SAW device using bimorph ZnO and Al structures, including those fabricated as Al foils or plates, to achieve breath tracking based on humidity and temperature changes. We applied open-source electronics and provided embedded computing characteristics for signal processing, data recognition, storage, and transmission of breath signals. We show that the thin-film SAW device out-performed standard and off-the-shelf capacitive electronic sensors in terms of their response and accuracy for human breath-tracking purposes. This in combination with embedded electronics makes a suitable platform for human breath monitoring and sleep disorder recognition. HIGHLIGHTS: • An open-source system for sleep disorder monitoring is developed. • An embedded platform using SAW sensors achieves fast response and accuracy. • A proof-of-concept breath-tracking system is provided. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Spatial distribution of biological cells plays a key role in tissue engineering for reconstituting the cellular microenvironment, and recently, acoustofluidics are explored as a viable tool for controlling structures in tissue fabrication because of its good biocompatibility, low‐power consumption, automation capability, nature of non‐invasive, and non‐contact. Herein, a reusable acoustofluidic device is developed using surface acoustic waves for manipulating microparticles/cells to form a 3D matrix pattern inside a scaffold‐based hydrogel contained in a millimetric chamber. The 3D patterned and polymerized hydrogel construct can be easily and safely removed from the chamber using a proposed lifting technique, which prevent any physical damages or contaminations and promote the reusability of the chamber. The generated 3D patterns of microparticles and cells are numerically studied using a finite‐element method, which is well validated by the experimental results. The proposed acoustofluidic device is a useful tool for in vitro engineering 3D scaffold‐based artificial tissues for drug and toxicity testing and building organs‐on‐chip applications. [ABSTRACT FROM AUTHOR]

Nanocrystalline ZnO films with strong (0002) texture and fine grains were deposited onto ultra-nanocrystalline diamond (UNCD) layers on silicon using high target utilization sputtering technology. The unique characteristic of this sputtering technique allows room temperature growth of smooth ZnO films with a low roughness and low stress at high growth rates. Surface acoustic wave (SAW) devices were fabricated on ZnO/UNCD structure and exhibited good transmission signals with a low insertion loss and a strong side-lobe suppression for the Rayleigh mode SAW. Based on the optimization of the layered structure of the SAW device, a good performance with a coupling coefficient of 5.2% has been realized, promising for improving the microfluidic efficiency in droplet transportation comparing with that of the ZnO/Si SAW device. An optimized temperature coefficient of frequency of −23.4 ppm °C−1 was obtained for the SAW devices with the 2.72 µm-thick ZnO and 1.1 µm-thick UNCD film. Significant thermal effect due to the acoustic heating has been redcued which is related to the temperature stability of the ZnO/UNCD SAW device. [ABSTRACT FROM AUTHOR]

• Successfully integrated closed-loop control strategy into SAW device to build an acoustofluidic closed-loop control system. • Experimentally demonstrated the precise and reliable control of single microparticle in three-dimensional space. • System principle and biocompatibility are verified by the experimental tests on the breast cancer cells. • Experimentally demonstrated separation of larger size microparticles when being controlled at speed limit. Precise, automatic and reliable position control of micro-objects such as single particles, biological cells or bio-organisms is critical for applications in biotechnology and tissue engineering. However, conventional acoustofluidic techniques generally lack reliability and automation capability thus are often incapable of building an efficient and automated system where the biological cells need to be precisely manipulated in three dimensions (3D). To overcome these limitations, we developed an acoustofluidic closed-loop control system which is combined with computer vision techniques and standing surface acoustic waves (SSAWs) to implement selective, automatic and precise position control of an object, such as a single cell or microparticle in a microfluidic chamber. Position of the object is in situ extracted from living images that are captured from a video camera. By utilizing the closed-loop control strategy, the object is precisely moved to the desired location in 3D patterns or along designed trajectories by manipulating the phase angle and power signal of the SSAWs. Controlling of breast cancer cells has been conducted to verify the principle and biocompatibility of the control system. This system could be employed to build an automatic system for cell analysis, cell isolation, self-assembling of materials into complex microstructures, or lab-on-chip and organ-on-chip applications. [ABSTRACT FROM AUTHOR]

Droplet deformation and force analysis on the inclined surface driven by the SAW. • Acoustofluidics along inclined surfaces have been investigated using AlN/Si Rayleigh surface acoustic waves. • At the inclination angle of 90°, a higher threshold pumping power is needed. • Effects of surface inclination angle on the jetting angle can be neglected for droplets with volume less than 2 μL. • AlN/Si SAWs can be used for both actuators and acoustic heaters to achieve potential lab-on-a-chip applications. Conventional acoustofluidics are restricted to manipulation of droplets on a flat surface, and there is an increasing demand for acoustofluidic devices to be performed at inclined surfaces to facilitate multilayered microfluidic device design and enhance system compactness. This paper reports theoretical and experimental studies of acoustofluidic behaviors (including transportation/pumping and jetting) along inclined surfaces using AlN/Si Rayleigh surface acoustic waves (SAWs). It has been demonstrated that for droplets with volume smaller than 3 μL, they could be efficiently transported on arbitrary inclined surfaces. The gravity effect would play a more and more important role in uphill climbing with the increased inclination angle. When the inclination angle was increased up to 90°, a higher threshold power was needed to transport the droplet and the maximum droplet volume which can be pumped also reached its minimum value. Effects of surface inclination angle on droplet jetting angles could be neglected for their volumes less than 2 μL. Moreover, microfluidic and acoustic heating performances of AlN/Si SAWs were further studied and compared with those conventional ZnO/Si SAWs with the same electrode configurations. [ABSTRACT FROM AUTHOR]