Surface acoustic wave (SAW) techniques in tissue engineering

Simple, and highly efficient edge-effect surface acoustic wave atomizer

Conventional surface acoustic wave (SAW) atomizers require a direct water supply on the surface, which can be complex and cumbersome. This paper presents a novel SAW atomizer that uses lateral acoustic wetting to achieve atomization without a direct water supply. The device works by simply pressing a piece of wetted paper strip against the bottom of an excited piezoelectric transducer. The liquid then flows along the side to the unmodified surface edge, where it is atomized into a well-converging mist in a stable and sustainable manner. We identified this phenomenon as the edge effect, using numerical simulation results of surface displacement mode. The feasibility of the prototype design was demonstrated by observing and investigating the integrated process of liquid extraction, transport, and atomization. We further explored the hydrodynamic principles of the change and breakup in liquid film geometry under different input powers. Experiments demonstrate that our atomizer is capable of generating high-quality fine liquid particles stably and rapidly even at very high input power. Compared to conventional SAW atomizer, the dispersion of mist width can be scaled down by 70%, while the atomization rate can be increased by 37.5%. Combined with the advantages of easy installation and robustness, the edge effect-based atomizer offers an attractive alternative to current counterparts for applications requiring high efficiency and miniaturization, such as simultaneous synthesis and encapsulation of nanoparticles, pulmonary drug delivery and portable inhalation therapy.

Bioprinting Using Organ Building Blocks: Spheroids, Organoids, and Assembloids

Three-dimensional (3D) bioprinting, a promising advancement in tissue engineering technology, involves the robotic, layer-by-layer additive biofabrication of functional 3D tissue and organ constructs. This process utilizes biomaterials, typically hydrogels and living cells, following digital models. Traditional tissue engineering uses a classic triad of living cells, scaffolds, and physicochemical signals in bioreactors. A scaffold is a temporary, often biodegradable, support structure. Tissue engineering primarily falls into two categories: (i) scaffold based and (ii) scaffold free. The latter, scaffold-free 3D bioprinting, is gaining increasing popularity. Organ building blocks (OBB), capable of self-assembly and self-organization, such as tissue spheroids, organoids, and assembloids, have begun to be utilized in scaffold-free bioprinting. This article discusses the expanding range of OBB, presents the rapidly evolving collection of bioprinting and bioassembly methods using these OBB, and finally, outlines the advantages, challenges, and future perspectives of using OBB in organ printing.

Cavity-agnostic acoustofluidic manipulations enabled by guided flexural waves on a membrane acoustic waveguide actuator

This article presents an in-depth exploration of the acoustofluidic capabilities of guided flexural waves (GFWs) generated by a membrane acoustic waveguide actuator (MAWA). By harnessing the potential of GFWs, cavity-agnostic advanced particle manipulation functions are achieved, unlocking new avenues for microfluidic systems and lab-on-a-chip development. The localized acoustofluidic effects of GFWs arising from the evanescent nature of the acoustic fields they induce inside a liquid medium are numerically investigated to highlight their unique and promising characteristics. Unlike traditional acoustofluidic technologies, the GFWs propagating on the MAWA's membrane waveguide allow for cavity-agnostic particle manipulation, irrespective of the resonant properties of the fluidic chamber. Moreover, the acoustofluidic functions enabled by the device depend on the flexural mode populating the active region of the membrane waveguide. Experimental demonstrations using two types of particles include in-sessile-droplet particle transport, mixing, and spatial separation based on particle diameter, along with streaming-induced counter-flow virtual channel generation in microfluidic PDMS channels. These experiments emphasize the versatility and potential applications of the MAWA as a microfluidic platform targeted at lab-on-a-chip development and showcase the MAWA's compatibility with existing microfluidic systems.

Acoustic Actuators for the Manipulation of Micro/Nanorobots: State-of-the-Art and Future Outlooks

Compared to other actuating methods, acoustic actuators offer the distinctive capability of the contactless manipulation of small objects, such as microscale and nanoscale robots. Furthermore, they have the ability to penetrate the skin, allowing for the trapping and manipulation of micro/nanorobots that carry therapeutic agents in diverse media. In this review, we summarize the current progress in using acoustic actuators for the manipulation of micro/nanorobots used in various biomedical applications. First, we introduce the actuating method of using acoustic waves to manipulate objects, including the principle of operation and different types of acoustic actuators that are usually employed. Then, applications involving manipulating different types of devices are reviewed, including bubble-based microrobots, bubble-free robots, biohybrid microrobots, and nanorobots. Finally, we discuss the challenges and future perspectives for the development of the field.

Cell-Based Micro/Nano-Robots for Biomedical Applications: A Review

Micro/nano-robots are powerful tools for biomedical applications and are applied in disease diagnosis, tumor imaging, drug delivery, and targeted therapy. Among the various types of micro-robots, cell-based micro-robots exhibit unique properties because of their different cell sources. In combination with various actuation methods, particularly externally propelled methods, cell-based microrobots have enormous potential for biomedical applications. This review introduces recent progress and applications of cell-based micro/nano-robots. Different actuation methods for micro/nano-robots are summarized, and cell-based micro-robots with different cell templates are introduced. Furthermore, the review focuses on the combination of cell-based micro/nano-robots with precise control using different external fields. Potential challenges, further prospects, and clinical translations are also discussed.

A review of acoustofluidic separation of bioparticles

Acoustofluidics is an emerging interdisciplinary research field that involves the integration of acoustics and microfluidics to address challenges in various scientific areas. This technology has proven to be a powerful tool for separating biological targets from complex fluids due to its label-free, biocompatible, and contact-free nature. Considering a careful designing process and tuning the acoustic field particles can be separated with high yield. Recently the advancement of acoustofluidics led to the development of point-of-care devices for separations of micro particles which address many of the limitations of conventional separation tools. This review article discusses the working principles and different approaches of acoustofluidic separation and provides a synopsis of its traditional and emerging applications, including the theory and mechanism of acoustofluidic separation, blood component separation, cell washing, fluorescence-activated cell sorting, circulating tumor cell isolation, and exosome isolation. The technology offers great potential for solving clinical problems and advancing scientific research.

Sonomechanobiology: Vibrational stimulation of cells and its therapeutic implications

All cells possess an innate ability to respond to a range of mechanical stimuli through their complex internal machinery. This comprises various mechanosensory elements that detect these mechanical cues and diverse cytoskeletal structures that transmit the force to different parts of the cell, where they are transcribed into complex transcriptomic and signaling events that determine their response and fate. In contrast to static (or steady) mechanostimuli primarily involving constant-force loading such as compression, tension, and shear (or forces applied at very low oscillatory frequencies (≤ 1 Hz) that essentially render their effects quasi-static), dynamic mechanostimuli comprising more complex vibrational forms (e.g., time-dependent, i.e., periodic, forcing) at higher frequencies are less well understood in comparison. We review the mechanotransductive processes associated with such acoustic forcing, typically at ultrasonic frequencies (> 20 kHz), and discuss the various applications that arise from the cellular responses that are generated, particularly for regenerative therapeutics, such as exosome biogenesis, stem cell differentiation, and endothelial barrier modulation. Finally, we offer perspectives on the possible existence of a universal mechanism that is common across all forms of acoustically driven mechanostimuli that underscores the central role of the cell membrane as the key effector, and calcium as the dominant second messenger, in the mechanotransduction process.

A microfluidic immunosensor for automatic detection of carcinoembryonic antigen based on immunomagnetic separation and droplet arrays

Diagnosis of cancer by biomarkers plays an important role in human health and life. However, current laboratory techniques for detecting cancer biomarkers still require laborious and time-consuming operation by skilled operators and associated laboratory instruments. This work presents a colorimetric biosensor for the rapid and sensitive detection of carcinoembryonic antigen (CEA) based on an automated immunomagnetic separation platform and a droplet array microfluidic chip with the aid of an image analysis system. Immunomagnetic nanoparticles (MNPs) were used to capture CEA in the samples. CEA-detecting antibodies and horseradish peroxidase (HRP) were modified on polystyrene microspheres (PS), catalysing hydrogen peroxide and 3,3',5,5'-tetramethylbenzidine (TMB) as signal outputs. Color reaction data were analyzed to establish a CEA concentration standard curve. The movement of MNPs between droplets in the microfluidic chip is achieved using an automatically programmable magnetic control system. This colorimetric biosensor has been used for the simultaneous detection of six CEA samples ranging from 100 pg mL^-1 to 100 ng mL^-1 with a detection limit of 14.347 pg mL^-1 in 10 min, following the linear equation: y = -4.773 ln(x) + 156.26 with a correlation of R² = 0.9924, and the entire workflow can be completed within 80 minutes. The microfluidic immunosensor designed in this paper has the advantages of low cost, automation, low sample consumption, high throughput, and promising applications in biochemistry.