Controlling cell-cell interactions using surface acoustic waves

Reconfigurable acoustic tweezer for precise tracking and in-situ sensing of trace miRNAs in tumor cells

MicroRNAs (miRNAs) have emerged as critical biomarkers for early cancer diagnosis and monitoring. However, their isolation from clinical samples typically yields only trace amounts, significantly limiting the sensitivity and efficiency of cancer detection. To address this challenge, we present a octangular reconfigurable acoustic tweezer (ORAT) as an integrated platform for precise tumor cell tracking and in-situ detection of trace miRNAs. By simultaneously modulating multidirectional acoustic signals and parameters, the ORAT dynamically reshapes the acoustic field, enabling precise control over manipulation areas, particle spacing, array angles, distribution patterns, and node rotation. This device allows selective particle manipulation across entire regions or specific areas through adaptive adjustments of the microchamber boundary. Notably, the ORAT achieves rapid and accurate localization and labeling of rare tumor cells within a large population of normal cells. Furthermore, it enhances the sensitivity of CRISPR/Cas-based miRNA detection in digital microdroplets by three orders of magnitude, if compared to that of the conventional tube-based method. With its versatile capabilities, the ORAT holds remarkable promise for advancing nucleic acid analysis in a wide range of cancers and related diseases.

A SAW-driven modular acoustofluidic tweezer

In surface acoustic wave (SAW)-driven acoustofluidic tweezers (AFTs), most setups are integrated on a piezoelectric substrate for a single purpose, limiting the reusability and versatility of devices fabricated using complex MEMS technologies. Meanwhile, prevalent devices exhibit anisotropy in SAW excitation and propagation, as well as optical birefringence and limited transmittance. This work presents a SAW-driven modular acoustofluidic tweezer consisting of up to four replaceable interdigital transducer (IDT) modules and a function module assembled on a common base. Since the IDT modules are separated, each can be fabricated using the piezoelectric substrate best suited to the requirements. For example, SAWs generated from different directions can simultaneously propagate along the X-axis of 128° Y-cut LiNbO3, enabling highly efficient excitations. The generated SAWs couple into the function module with excellent optical properties and convert into Lamb waves, which then leak into the microfluidic domain and act on the fluid/particles. All modules are connected via standardized interfaces, eliminating potential instabilities caused by wired connections. The reliability of the setup is demonstrated via particle/cell patterning, separation, and concentration experiments, during which the replaceability and reusability of different modules, and the other advantages of the setup, e.g., simple assembly, ease of operation, and application flexibility, are proven.

An acoustofluidic embedding platform for rapid multiphase microparticle injection

Droplet manipulation technologies play a critical role in many aspects of biochemical research, including in complex reaction assays useful for drug delivery, for building artificial cells, and in synthetic biology. While advancements have been made in manipulating liquid droplets, the capability to freely and dynamically manipulate solid objects across aqueous and oil phases remains unexplored. Here, we develop an acoustofluidic frequency-associated microsphere embedding platform, which enables microscale rapid injection of microparticles from a fluorinated oil into aqueous droplets. By observing different embedding mechanisms at low and high acoustic frequencies, we establish a theoretical model and practical principles for cross-phase manipulations. The proposed system not only enables multi-phase manipulation but also provides contactless control of specific microparticles within various distinctive phases. We demonstrate the acoustic-driven embedding and subsequent on-demand disassembly of hydrogel microspheres. This system indicates potential for reagent delivery and molecule capture applications. It enhances existing droplet manipulation technologies by enabling both multi-phase and cross-phase operations, paving the way for solid-liquid interaction studies in artificial cell research. The capability for intricate multi-phase loading, transport, and reactions offers promising implications for various fields, including in-droplet biochemical assays, drug delivery, and synthetic biology.

Biological Acoustic Levitation and Its Potential Application for Microgravity Study

The open and contactless environment of acoustic levitation provides a unique condition in experimenting with varying substances while levitated for observation and implementation with other devices, with recent improvements in cost and accessibility. We briefly decipher the theory behind acoustic levitation and describe currently available levitation platforms. Then, how these platforms have been employed in biological applications is reviewed. Intriguingly, recent researches indicated the viability of acoustic levitation to be utilized as a microgravity simulator. We introduce existing on-ground microgravity platforms, and discuss the potential of acoustic levitation in simulating microgravity. Acoustic levitation could be an alternative to microgravity platforms such as clinostats while allowing for novel microgravity research. On the other hand, the microgravity provided by acoustic levitation may be restricted due to potential limitations in the available levitation volume, relatively larger gravity compared to 10-3 g centrifugal acceleration from clinostats, and probable instability due to air perturbations and acoustic streaming. With more knowledge about in-droplet particle rotation and the regulatory factors during levitation, acoustic levitation may provide a new and advanced platform for microgravity simulation via taking advantage of its availability for real-time observation and manipulation of samples via added instrumentation while samples are levitated in a simulated microgravity condition.

Extracellular vesicle-based point-of-care testing for diagnosis and monitoring of Alzheimer's disease

Extracellular vesicles (EVs) show potential for early diagnosis of Alzheimer's disease (AD) and monitoring of its progression. However, EV-based AD diagnosis faces challenges due to the small size and low abundance of biomarkers. Here, we report a fully integrated organic electrochemical transistor (OECT) sensor for ultrafast, accurate, and convenient point-of-care testing (POCT) of serum EVs from AD patients. By utilizing acoustoelectric enrichment, the EVs can be quickly propelled, significantly enriched, and specifically bound to the OECT detection area, achieving a gain of over 280 times response in 30 s. The integrated POCT sensor can detect serum EVs from AD patients with a limit of detection as low as 500 EV particles/mL and a reduced detection time of just two minutes. Furthermore, the integrated POCT sensors were used to monitor AD progression in an AD mouse model by testing the mouse Aβ EVs at different time courses (up to 18 months) and compared with the Aβ accumulation using high-resolution magnetic resonance imaging (MRI). This innovative technology has the potential for accurate and rapid diagnosis of Alzheimer's and other neurodegenerative diseases, and monitoring of disease progression and treatment response.

Large-scale acoustic single cell trapping and selective releasing

Recent advancements in single-cell analysis have underscored the need for precise isolation and manipulation of individual cells. Traditional techniques for single-cell manipulation are often limited by the number of cells that can be parallel trapped and processed and usually require complex devices or instruments to operate. Here, we introduce an acoustic microfluidic platform that efficiently traps and selectively releases individual cells using spherical air cavities embedded in a polydimethylsiloxane (PDMS) substrate for large scale manipulation. Our device utilizes the principle of acoustic impedance mismatches to generate near-field acoustic potential gradients that create trapping sites for single cells. These single cell traps can be selectively disabled by illuminating a near-infrared laser pulse, allowing targeted release of trapped cells. This method ensures minimal impact on cell viability and proliferation, making it ideal for downstream single-cell analysis. Experimental results demonstrate our platform's capability to trap and release synthetic microparticles and biological cells with high efficiency and biocompatibility. Our device can handle a wide range of cell sizes (8-30 μm) across a large active manipulation area of 1 cm2 with 20 000 single-cell traps, providing a versatile and robust platform for single-cell applications. This acoustic microfluidic platform offers a cost-effective and practical method for large scale single-cell trapping and selective releasing with potential applications in genomics, proteomics, and other fields requiring precise single-cell manipulation.

Scalable acoustic virtual stirrer for enhanced interfacial enzymatic nucleic acid reactions

Enzymatic nucleic acid reaction is a fundamental tool in molecular biology. However, high-complexity enzymatic DNA reactions and assays are still challenging due to the difficulties in integrating and scaling up microscale reaction units and mixing tools. Here, we present scalable acoustofluidic platform featuring acoustic virtual stirrer (AVS) arrays, serving as stirrers to increase the efficiency of interfacial enzymatic nucleic acid reactions. Analogous to magnetic stirrers, AVS arrays perturb the fluid through oscillating pressure nodes, controllable in terms of speeds and amplitudes via modulation. By optimizing the kinetics of surface-tethered DNA and enzymes via AVS, we achieve a 7.74% improvement in the stepwise yield of enzymatic DNA synthesis. In addition, the AVS enhanced DNA logic gate architecture can complete responses within 2 minutes, achieving average speed enhancement of 8.58 times compared to the non-AVS configuration. With its tunability, ease of integration, and efficiency, this technology holds promises for applications in biology and chemistry.

Single Cell-Pair Proteomics for Decoding Immune-Cancer Cell Interactions

The efficacy of cancer immunotherapy is significantly influenced by the heterogeneity of individual tumors and immune responses. To investigate this phenomenon, a microfluidic platform is constructed for profiling immune-cancer cell interactions at the single-cell proteomics level for the first time. Based on the platform, a comprehensive workflow is proposed for achieving accurate single-cell pairing of an immune cell and a cancer cell with low cell damage and high success rate up to 95%, cell pair co-culture, and real-time microscopic monitoring of the cell-pair interactions, cell pair retrieval, mass spectrometry-based proteomic analysis of singe cell pairs, and decoupling of the proteomic information for each cell within the cell pair with the stable-isotope labeling method. With the workflow, the interactions of single natural killer (NK) cells and single K562 tumor cells are investigated based on real-time images and single cell-pair proteomics. Notably, an identification depth of over 1000 protein groups in a single cell-pair is achieved, leading to the discovery of sub-clusters of NK cells with different functions and the identification of important biomarkers for cancer treatments. This demonstrates the unique capability of the present platform in providing substantial and comprehensive datasets for profiling immune-cancer cell interactions, discovering heterogeneous immune responses, and predicting biomarkers in the study of cancer immunotherapy.

Numerical investigation of acoustic radiation force and microstreaming in a viscoelastic fluid

We present a numerical model to study time-averaged acoustic radiation force and microstreaming around an elastic sphere immersed within an acoustically actuated viscoelastic fluid. We employ a perturbation approach to systematically identify limiting regimes where the viscoelastic fluid can be approximated as a purely viscous fluid at the acoustic and mean time scales. Unlike existing numerical models, we account for microstreaming and fluid elasticity contributions to the radiation force. We elucidate the inherent assumptions within reduced expressions considered in prior numerical models and highlight the divergence between the acoustic radiation force obtained from the reduced and general expressions. We also discuss numerical considerations to ensure the invariance of the acoustic radiation force with the choice of integration surface by recasting the time-averaged mass balance equation in terms of Stokes drift. Our results reveal that the acoustic radiation force exhibits a peak value for an optimal relaxation time, and both the peak acoustic radiation force and the optimal relaxation time increase with increasing polymer viscosity. The results also highlight the significant contribution of fluid elasticity to the radiation force and invalidate the previously employed reduced acoustic radiation force expressions for general viscoelastic regime.

Advances in Microsphere-Based Super-Resolution Imaging

Techniques to resolve images beyond the diffraction limit of light with a large field of view (FOV) are necessary to foster progress in various fields such as cell and molecular biology, biophysics, and nanotechnology, where nanoscale resolution is crucial for understanding the intricate details of large-scale molecular interactions. Although several means of achieving super-resolutions exist, they are often hindered by factors such as high costs, significant complexity, lengthy processing times, and the classical tradeoff between image resolution and FOV. Microsphere-based super-resolution imaging has emerged as a promising approach to address these limitations. In this review, we delve into the theoretical underpinnings of microsphere-based imaging and the associated photonic nanojet. This is followed by a comprehensive exploration of various microsphere-based imaging techniques, encompassing static imaging, mechanical scanning, optical scanning, and acoustofluidic scanning methodologies. This review concludes with a forward-looking perspective on the potential applications and future scientific directions of this innovative technology.

Profiling signaling mediators for cell-cell interactions and communications with microfluidics-based single-cell analysis tools

Cell-cell interactions and communication represent the fundamental cornerstone of cells' collaborative efforts in executing diverse biological processes. A profound understanding of how cells interface through various mediators is pivotal across a spectrum of biological systems. Recent strides in microfluidic technologies have significantly bolstered the precision and prowess in capturing and manipulating cells with exceptional spatial and temporal resolution. These advanced methodologies converge with multi-signal mediator detection systems, furnishing potent, high-throughput platforms for dissecting cell-cell interactions at the single-cell level. This approach empowers researchers to delve into intricate cellular dynamics with unprecedented accuracy and efficiency. Here, we present a critical evaluation of the latest advancements in microfluidics-driven techniques for detecting signal mediators involved in cell-cell interactions and communication at the single-cell level. We underscore notable biological applications that have benefited from these technologies and identify pressing challenges that must be addressed in future endeavors leveraging microfluidic tools for single-cell interaction studies.

Intelligent sensing for the autonomous manipulation of microrobots toward minimally invasive cell surgery

The physiology and pathogenesis of biological cells have drawn enormous research interest. Benefiting from the rapid development of microfabrication and microelectronics, miniaturized robots with a tool size below micrometers have widely been studied for manipulating biological cells in vitro and in vivo. Traditionally, the complex physiological environment and biological fragility require human labor interference to fulfill these tasks, resulting in high risks of irreversible structural or functional damage and even clinical risk. Intelligent sensing devices and approaches have been recently integrated within robotic systems for environment visualization and interaction force control. As a consequence, microrobots can be autonomously manipulated with visual and interaction force feedback, greatly improving accuracy, efficiency, and damage regulation for minimally invasive cell surgery. This review first explores advanced tactile sensing in the aspects of sensing principles, design methodologies, and underlying physics. It also comprehensively discusses recent progress on visual sensing, where the imaging instruments and processing methods are summarized and analyzed. It then introduces autonomous micromanipulation practices utilizing visual and tactile sensing feedback and their corresponding applications in minimally invasive surgery. Finally, this work highlights and discusses the remaining challenges of current robotic micromanipulation and their future directions in clinical trials, providing valuable references about this field.

Sound innovations for biofabrication and tissue engineering

Advanced biofabrication techniques can create tissue-like constructs that can be applied for reconstructive surgery or as in vitro three-dimensional (3D) models for disease modeling and drug screening. While various biofabrication techniques have recently been widely reviewed in the literature, acoustics-based technologies still need to be explored. The rapidly increasing number of publications in the past two decades exploring the application of acoustic technologies highlights the tremendous potential of these technologies. In this review, we contend that acoustics-based methods can address many limitations inherent in other biofabrication techniques due to their unique advantages: noncontact manipulation, biocompatibility, deep tissue penetrability, versatility, precision in-scaffold control, high-throughput capabilities, and the ability to assemble multilayered structures. We discuss the mechanisms by which acoustics directly dictate cell assembly across various biostructures and examine how the advent of novel acoustic technologies, along with their integration with traditional methods, offers innovative solutions for enhancing the functionality of organoids. Acoustic technologies are poised to address fundamental challenges in biofabrication and tissue engineering and show promise for advancing the field in the coming years.

Acoustofluidic tweezers via ring resonance

Ring resonator (RR) devices are closed-loop waveguides where waves circulate only at the resonant frequencies. They have been used in sensor technology and optical tweezers, but controlling micron-scale particles with optical RR tweezers is challenging due to insufficient force, short working distances, and photodamage. To overcome these obstacles, an acoustofluidic RR-based tweezing method is developed to manipulate micro-sized particles that can enhance particle trapping through the resonance interaction of acoustic waves with high Q factor (>3000), more than 20 times greater than traditional acoustic transducers. Particles can be precisely manipulated within the RR by adjusting the signal phase, with trapping amplified by enlarging the connected waveguide. Rapid particle mixing is achieved when particles are placed between the waveguide and RR. The signal path is strengthened by strategically positioning the RR in a two-dimensional plane. Acoustofluidic RR tweezers have immense potential for advancing applications in biosensing, mechanobiology, lab-on-a-chip, and cell-cell communication research.

Sonodynamic and Acoustically Responsive Nanodrug Delivery System: Cancer Application

The advent of acoustically responsive nanodrugs that are specifically optimized for sonodynamic therapy (SDT) is a novel approach for clinical applications. Examining the therapeutic applications of sono-responsive drug delivery systems, understanding their dynamic response to acoustic stimuli, and their crucial role in enhancing targeted drug delivery are intriguing issues for current cancer treatment. Specifically, the suggested review covers SDT, a modality that enhances the cytotoxic activity of specific compounds (sonosensitizers) using ultrasound (US). Notably, SDT offers significant advantages in cancer treatment by utilizing US energy to precisely target and activate sonosensitizers toward deep-seated malignant sites. The potential mechanisms underlying SDT involve the generation of radicals from sonosensitizers, physical disruption of cell membranes, and enhanced drug transport into cells via US-assisted sonoporation. In particular, SDT is emerging as a promising modality for noninvasive, site-directed elimination of solid tumors. Given the complexity and diversity of tumors, many studies have explored the integration of SDT with other treatments to enhance the overall efficacy. This trend has paved the way for SDT-based multimodal synergistic cancer therapies, including sonophototherapy, sonoimmunotherapy, and sonochemotherapy. Representative studies of these multimodal approaches are comprehensively presented, with a detailed discussion of their underlying mechanisms. Additionally, the application of audible sound waves in biological systems is explored, highlighting their potential to influence cellular processes and enhance therapeutic outcomes. Audible sound waves can modulate enzyme activities and affect cell behavior, providing novel avenues for the use of sound-based techniques in medical applications. This review highlights the current challenges and prospects in the development of SDT-based nanomedicines in this rapidly evolving research field. The anticipated growth of this SDT-based therapeutic approach promises to significantly improve the precision of cancer treatment.

An Acoustofluidic Picoinjector

Droplet microfluidics has emerged as a valuable technology for a multitude of chemical and biomedical applications, offering the capability to create independent microenvironments for high-throughput assays. Central to numerous droplet microfluidic applications is the picoinjection of materials into individual droplets, yet existing picoinjection methods often exhibit high power requirements, lack biocompatibility, and/or suffer from limited controllability. Here, we present an acoustofluidic picoinjector that generates acoustic pressure at the droplet interface to enable on-demand, energy-efficient, and biocompatible injection at high precision. We validate our platform by performing acid-base titrations by iteratively injecting picoliter volume reagents into droplets to induce pH transitions detectable by color change in solution. Additionally, we demonstrate the versatility of the acoustofluidic picoinjector in the synthesis of metallic nanoparticles, yielding highly monodisperse and reproducible particle morphologies compared to conventional bulk-phase techniques. By facilitating controlled delivery of reagents or biological samples with unparalleled accuracy, acoustofluidic picoinjection broadens the utility of droplet microfluidics for a myriad of applications in chemical and biological research.

Recent Advancements in High-Frequency Ultrasound Applications from Imaging to Microbeam Stimulation

Ultrasound is a versatile and well-established technique using sound waves with frequencies higher than the upper limit of human hearing. Typically, therapeutic and diagnosis ultrasound operate in the frequency range of 500 kHz to 15 MHz with greater depth of penetration into the body. However, to achieve improved spatial resolution, high-frequency ultrasound (>15 MHz) was recently introduced and has shown promise in various fields such as high-resolution imaging for the morphological features of the eye and skin as well as small animal imaging for drug and gene therapy. In addition, high-frequency ultrasound microbeam stimulation has been demonstrated to manipulate single cells or microparticles for the elucidation of physical and functional characteristics of cells with minimal effect on normal cell physiology and activity. Furthermore, integrating machine learning with high-frequency ultrasound enhances diagnostics, including cell classification, cell deformability estimation, and the diagnosis of diabetes and dysnatremia using convolutional neural networks (CNNs). In this paper, current efforts in the use of high-frequency ultrasound from imaging to stimulation as well as the integration of deep learning are reviewed, and potential biomedical and cellular applications are discussed.

Sensors and Devices Guided by Artificial Intelligence for Personalized Pain Medicine

Personalized pain medicine aims to tailor pain treatment strategies for the specific needs and characteristics of an individual patient, holding the potential for improving treatment outcomes, reducing side effects, and enhancing patient satisfaction. Despite existing pain markers and treatments, challenges remain in understanding, detecting, and treating complex pain conditions. Here, we review recent engineering efforts in developing various sensors and devices for addressing challenges in the personalized treatment of pain. We summarize the basics of pain pathology and introduce various sensors and devices for pain monitoring, assessment, and relief. We also discuss advancements taking advantage of rapidly developing medical artificial intelligence (AI), such as AI-based analgesia devices, wearable sensors, and healthcare systems. We believe that these innovative technologies may lead to more precise and responsive personalized medicine, greatly improved patient quality of life, increased efficiency of medical systems, and reducing the incidence of addiction and substance use disorders.

STIE: Single-cell level deconvolution, convolution, and clustering in in situ capturing-based spatial transcriptomics

In in situ capturing-based spatial transcriptomics, spots of the same size and printed at fixed locations cannot precisely capture the randomly-located single cells, therefore inherently failing to profile transcriptome at the single-cell level. To this end, we present STIE, an Expectation Maximization algorithm that aligns the spatial transcriptome to its matched histology image-based nuclear morphology and recovers missing cells from ~70% gap area, thereby achieving the real single-cell level and whole-slide scale deconvolution, convolution, and clustering for both low- and high-resolution spots. STIE characterizes cell-type-specific gene expression and demonstrates outperforming concordance with true cell-type-specific transcriptomic signatures than the other spot- and subspot-level methods. Furthermore, STIE reveals the single-cell level insights, for instance, lower actual spot resolution than its reported spot size, unbiased evaluation of cell type colocalization, superior power of high-resolution spot in distinguishing nuanced cell types, and spatial cell-cell interactions at the single-cell level other than spot level.

Sound Matrix Shaping of Living Matter: From Macrosystems to Cell Microenvironment, Where Mitochondria Act as Energy Portals in Detecting and Processing Sound Vibrations

Vibration and sound are the shaping matrix of the entire universe. Everything in nature is shaped by energy vibrating and communicating through its own sound trail. Every cell within our body vibrates at defined frequencies, generating its peculiar "sound signature". Mitochondria are dynamic, energy-transforming, biosynthetic, and signaling organelles that actively transduce biological information. Novel research has shown that the mitochondrial function of mammalian cells can be modulated by various energetic stimuli, including sound vibrations. Regarding acoustic vibrations, definite types of music have been reported to produce beneficial impacts on human health. In very recent studies, the effects of different sound stimuli and musical styles on cellular function and mitochondrial activity were evaluated and compared in human cells cultured in vitro, investigating the underlying responsible molecular mechanisms. This narrative review will take a multilevel trip from macro to intracellular microenvironment, discussing the intimate vibrational sound activities shaping living matter, delving deeper into the molecular mechanisms underlying the sound modulation of biological systems, and mainly focusing our discussion on novel evidence showing the competence of mitochondria in acting as energy portals capable of sensing and transducing the subtle informational biofields of sound vibration.

Acoustic vibration promotes in vitro expansion of human embryonic stem cells

OBJECTIVES

This study aimed to investigate the effect of acoustic vibration on the pluripotency of human embryonic stem cells (hESCs) and evaluate cell proliferation and self-renewal ability post-treatment.

METHODS

The human ES cell line H1 was used for the experiments. hESCs were treated with an acoustic vibration device. Their proliferative ability was subsequently detected using a colony formation assay, while the expression of pluripotency-related markers was detected via immunofluorescence staining. Finally, changes in gene expression levels were examined using quantitative polymerase chain reaction (qPCR) in the presence of appropriate primers.

RESULTS

Compared with normal cells in the control group, the morphology of experimental cells subjected to acoustic vibration did not significantly change. Contrastingly, the colony-forming efficiency of the experimental cells significantly increased. Immunofluorescence staining results showed the cells in experimental group were positive for the pluripotency markers NANOG, octamer-binding transcription factor 4 gene (OCT4), and SRY (sex determining region Y)-box 2 (SOX2). In addition, the expression levels of pluripotency genes NANOG, OCT4, SOX2, and Yes-associated protein (YAP)-related genes were up-regulated following acoustic vibration.

CONCLUSIONS

Our results revealed that acoustic vibration enhanced the proliferative ability of hESCs and increased the expression levels of NANOG, OCT4, SOX2, and YAP-related genes, indicating that acoustic vibration can optimize the self-renewal ability of hESCs and that the YAP signaling pathway may play a critical role in the functional process of acoustic vibration.

Three-Dimensional Bioprinting in Vascular Tissue Engineering and Tissue Vascularization of Cardiovascular Diseases

In the 21st century, significant progress has been made in repairing damaged materials through material engineering. However, the creation of large-scale artificial materials still faces a major challenge in achieving proper vascularization. To address this issue, researchers have turned to biomaterials and three-dimensional (3D) bioprinting techniques, which allow for the combination of multiple biomaterials with improved mechanical and biological properties that mimic natural materials. Hydrogels, known for their ability to support living cells and biological components, have played a crucial role in this research. Among the recent developments, 3D bioprinting has emerged as a promising tool for constructing hybrid scaffolds. However, there are several challenges in the field of bioprinting, including the need for nanoscale biomimicry, the formulation of hydrogel blends, and the ongoing complexity of vascularizing biomaterials, which requires further research. On a positive note, 3D bioprinting offers a solution to the vascularization problem due to its precise spatial control, scalability, and reproducibility compared with traditional fabrication methods. This paper aims at examining the recent advancements in 3D bioprinting technology for creating blood vessels, vasculature, and vascularized materials. It provides a comprehensive overview of the progress made and discusses the limitations and challenges faced in current 3D bioprinting of vascularized tissues. In addition, the paper highlights the future research directions focusing on the development of 3D bioprinting techniques and bioinks for creating functional materials.

Robot-assisted chirality-tunable acoustic vortex tweezers for contactless, multifunctional, 4-DOF object manipulation

Robotic manipulation of small objects has shown great potential for engineering, biology, and chemistry research. However, existing robotic platforms have difficulty in achieving contactless, high-resolution, 4-degrees-of-freedom (4-DOF) manipulation of small objects, and noninvasive maneuvering of objects in regions shielded by tissue and bone barriers. Here, we present chirality-tunable acoustic vortex tweezers that can tune acoustic vortex chirality, transmit through biological barriers, trap single micro- to millimeter-sized objects, and control object rotation. Assisted by programmable robots, our acoustic systems further enable contactless, high-resolution translation of single objects. Our systems were demonstrated by tuning acoustic vortex chirality, controlling object rotation, and translating objects along arbitrary-shaped paths. Moreover, we used our systems to trap single objects in regions with tissue and skull barriers and translate an object inside a Y-shaped channel of a thick biomimetic phantom. In addition, we showed the function of ultrasound imaging-assisted acoustic manipulation by monitoring acoustic object manipulation via live ultrasound imaging.

Irreversible Bonding of Polydimethylsiloxane-Lithium Niobate using Oxygen Plasma Modification for Surface Acoustic Wave based Microfluidic Application: Theory and Experiment

Acoustic microfluidic chips, fabricated by combining lithium niobate (LiNbO3) with polydimethylsiloxane (PDMS), practically find applications in biomedicine. However, high-strength direct bonding of LiNbO3 substrate with PDMS microchannel remains a challenge due to the large mismatching of thermal expansion coefficient at the interface and the lack of bonding theory. This paper elaborately reveals the bonding mechanisms of PDMS and LiNbO3, demonstrating an irreversible bonding method for PDMS-LiNbO3 heterostructures using oxygen plasma modification. An in-situ monitoring strategy by using resonant devices is proposed for oxygen plasma, including quartz crystal microbalance (QCM) covered with PDMS and surface acoustic wave (SAW) fabricated by LiNbO3. When oxygen plasma exposure occurs, surfaces are cleaned, oxygen ions are implanted, and hydroxyl groups (-OH) are formed. Upon interfaces bonding, the interface will form niobium-oxygen-silicon covalent bonds to realize an irreversible connection. A champion bonding strength is obtained of 1.1 MPa, and the PDMS-LiNbO3 acoustic microfluidic chip excels in leakage tests, withstanding pressures exceeding 60 psi, outperforming many previously reported devices. This work addresses the gap in PDMS-LiNbO3 bonding theory and advances its practical application in the acoustic microfluidic field.

Selective Acoustic Trapping, Translating, Rotating, and Orienting of Organism From Heterogeneous Mixture

Selective contactless manipulation of organisms with intrinsic mobility from heterogeneous mixture is essential for biomedical engineering and microbiology. Acoustic manipulation, compared to its optical, magnetic, and electrostatic counterparts, provides superior bio-compatibility and additive-free properties. In this study, we present an acoustic manipulation system capable of selectively trapping, translating, rotating, and orienting individual organisms from in-Petri dish organism mixture using a phased transducer array and microscope, by dynamically steering the acoustic field. Specifically, using brine shrimp and zebrafish populations as example, the to-be-manipulated organisms with different sizes or morphologies can be manually designated by the user in microscopic image and interactively localized. Thereafter, the selected organisms can be automatically trapped from the heterogeneous mixture using a multiple focal point-based acoustic field steering method. Finally, the trapped organisms can be translated, rotated, and oriented in regard to the user's distinct manipulation objectives in instant response. In different tasks, closed-loop positioning and real-time motion planning control are performed, highlighting the innovation in terms of automation and accuracy of our manipulation technique. The results demonstrate that our acoustic manipulation system and acoustic field steering method enable selective, stable, precision, real-time, and in-Petri dish manipulation of organisms from heterogeneous mixture.

A bio-fabricated tesla valves and ultrasound waves-powered blood plasma viscometer

Introduction: There is clinical evidence that the fresh blood viscosity is an important indicator in the development of vascular disorder and coagulation. However, existing clinical viscosity measurement techniques lack the ability to measure blood viscosity and replicate the in-vivo hemodynamics simultaneously. Methods: Here, we fabricate a novel digital device, called Tesla valves and ultrasound waves-powered blood plasma viscometer (TUBPV) which shows capacities in both viscosity measurement and coagulation monitoring. Results: Based on the Hagen-Poiseuille equation, viscosity analysis can be faithfully performed by a video microscopy. Tesla-like channel ensured unidirectional liquid motion with stable pressure driven that was triggered by the interaction of Tesla valve structure and ultrasound waves. In few seconds the TUBPV can generate an accurate viscosity profile on clinic fresh blood samples from the flow time evaluation. Besides, Tesla-inspired microchannels can be used in the real-time coagulation monitoring. Discussion: These results indicate that the TUBVP can serve as a point-of-care device in the ICU to evaluate the blood's viscosity and the anticoagulation treatment.

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.

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.

Aerosol jet printing of surface acoustic wave microfluidic devices

The addition of surface acoustic wave (SAW) technologies to microfluidics has greatly advanced lab-on-a-chip applications due to their unique and powerful attributes, including high-precision manipulation, versatility, integrability, biocompatibility, contactless nature, and rapid actuation. However, the development of SAW microfluidic devices is limited by complex and time-consuming micro/nanofabrication techniques and access to cleanroom facilities for multistep photolithography and vacuum-based processing. To simplify the fabrication of SAW microfluidic devices with customizable dimensions and functions, we utilized the additive manufacturing technique of aerosol jet printing. We successfully fabricated customized SAW microfluidic devices of varying materials, including silver nanowires, graphene, and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). To characterize and compare the acoustic actuation performance of these aerosol jet printed SAW microfluidic devices with their cleanroom-fabricated counterparts, the wave displacements and resonant frequencies of the different fabricated devices were directly measured through scanning laser Doppler vibrometry. Finally, to exhibit the capability of the aerosol jet printed devices for lab-on-a-chip applications, we successfully conducted acoustic streaming and particle concentration experiments. Overall, we demonstrated a novel solution-based, direct-write, single-step, cleanroom-free additive manufacturing technique to rapidly develop SAW microfluidic devices that shows viability for applications in the fields of biology, chemistry, engineering, and medicine.

Single-cell level deconvolution, convolution, and clustering in spatial transcriptomics by aligning spot level transcriptome to nuclear morphology

In spot-based spatial transcriptomics, spots that are of the same size and printed at the fixed location cannot precisely capture the actual randomly located single cells, therefore failing to profile the transcriptome at the single-cell level. The current studies primarily focused on enhancing the spot resolution in size via computational imputation or technical improvement, however, they largely overlooked that single-cell resolution, i.e., resolution in cellular or even smaller size, does not equal single-cell level. Using both real and simulated spatial transcriptomics data, we demonstrated that even the high-resolution spatial transcriptomics still has a large number of spots partially covering multiple cells simultaneously, revealing the intrinsic non-single-cell level of spot-based spatial transcriptomics regardless of spot size. To this end, we present STIE, an EM algorithm that aligns the spatial transcriptome to its matched histology image-based nuclear morphology and recovers missing cells from up to ~70% gap area between spots via the nuclear morphological similarity and neighborhood information, thereby achieving the real single-cell level and whole-slide scale deconvolution/convolution and clustering for both low- and high-resolution spots. On both real and simulation spatial transcriptomics data, STIE characterizes the cell-type specific gene expression variation and demonstrates the outperforming concordance with the single-cell RNAseq-derived cell type transcriptomic signatures compared to the other spot- and subspot-level methods. Furthermore, STIE enabled us to gain novel insights that failed to be revealed by the existing methods due to the lack of single-cell level, for instance, lower actual spot resolution than its reported spot size, the additional contribution of cellular morphology to cell typing beyond transcriptome, unbiased evaluation of cell type colocalization, superior power of high-resolution spot in distinguishing nuanced cell types, and spatially resolved cell-cell interactions at the single-cell level other than spot level. The STIE code is publicly available as an R package at https://github.com/zhushijia/STIE.

Microfluidic-based platforms for cell-to-cell communication studies

Intercellular communication is critical to the understanding of human health and disease progression. However, compared to traditional methods with inefficient analysis, microfluidic co-culture technologies developed for cell-cell communication research can reliably analyze crucial biological processes, such as cell signaling, and monitor dynamic intercellular interactions under reproducible physiological cell co-culture conditions. Moreover, microfluidic-based technologies can achieve precise spatial control of two cell types at the single-cell level with high throughput. Herein, this review focuses on recent advances in microfluidic-based 2D and 3D devices developed to confine two or more heterogeneous cells in the study of intercellular communication and decipher the advantages and limitations of these models in specific cellular research scenarios. This review will stimulate the development of more functionalized microfluidic platforms for biomedical research, inspiring broader interests across various disciplines to better comprehend cell-cell communication and other fields, such as tumor heterogeneity and drug screening.

Bioinspired Surfaces Derived from Acoustic Waves for On-Demand Droplet Manipulations

The controllable manipulation and transfer of droplets are fundamental in a wide range of chemical reactions and even life processes. Herein, we present a novel, universal, and straightforward acoustic approach to fabricating biomimetic surfaces for on-demand droplet manipulations like many natural creatures. Based on the capillary waves induced by surface acoustic waves, various polymer films could be deformed into pre-designed structures, such as parallel grooves and grid-like patterns. These structured and functionalized surfaces exhibit impressive ability in droplet transportation and water collection, respectively. Besides these static surfaces, the tunability of acoustics could also endow polymer surfaces with dynamic controllability for droplet manipulations, including programming wettability, mitigating droplet evaporation, and accelerating chemical reactions. Our approach is capable of achieving universal surface manufacturing and droplet manipulation simultaneously, which simplifies the fabrication process and eliminates the need for additional chemical modifications. Thus, we believe that our acoustic-derived surfaces and technologies could provide a unique perspective for various applications, including microreactor integration, biochemical reaction control, tissue engineering, and so on.

Acoustofluidic Engineering of Functional Vessel-on-a-Chip

Construction of in vitro vascular models is of great significance to various biomedical research, such as pharmacokinetics and hemodynamics, and thus is an important direction in the tissue engineering field. In this work, a standing surface acoustic wave field was constructed to spatially arrange suspended endothelial cells into a designated acoustofluidic pattern. The cell patterning was maintained after the acoustic field was withdrawn within the solidified hydrogel. Then, interstitial flow was provided to activate vessel tube formation. In this way, a functional vessel network with specific vessel geometry was engineered on-chip. Vascular function, including perfusability and vascular barrier function, was characterized by microbead loading and dextran diffusion, respectively. A computational atomistic simulation model was proposed to illustrate how solutes cross the vascular membrane lipid bilayer. The reported acoustofluidic methodology is capable of facile and reproducible fabrication of the functional vessel network with specific geometry and high resolution. It is promising to facilitate the development of both fundamental research and regenerative therapy.

Acoustophoresis around an elastic scatterer in a standing wave field

Acoustofluidic systems often employ prefabricated acoustic scatterers that perturb the imposed acoustic field to realize the acoustophoresis of immersed microparticles. We present a numerical study to investigate the time-averaged streaming and radiation force fields around a scatterer. Based on the streaming and radiation force field, we obtain the trajectories of the immersed microparticles with varying sizes and identify a critical transition size at which the motion of immersed microparticles in the vicinity of a prefabricated scatterer shifts from being streaming dominated to radiation dominated. We consider a range of acoustic frequencies to reveal that the critical transition size decreases with increasing frequency; this result explains the choice of acoustic frequencies in previously reported experimental studies. We also examine the impact of scatterer material and fluid properties on the streaming and radiation force fields, as well as on the critical transition size. Our results demonstrate that the critical transition size decreases with an increase in acoustic contrast factor: a nondimensional quantity that depends on material properties of the scatterer and the fluid. Our results provide a pathway to realize radiation force based manipulation of small particles by increasing the acoustic contrast factor of the scatterer, lowering the kinematic viscosity of the fluid, and increasing the acoustic frequency.

Acoustofluidic Engineering Functional Vessel-on-a-Chip

Construction of in vitro vascular models is of great significance to various biomedical research, such as pharmacokinetics and hemodynamics, thus is an important direction in tissue engineering. In this work, a standing surface acoustic wave field was constructed to spatially arrange suspended endothelial cells into a designated patterning. The cell patterning was maintained after the acoustic field was withdrawn by the solidified hydrogel. Then, interstitial flow was provided to activate vessel tube formation. Thus, a functional vessel-on-a-chip was engineered with specific vessel geometry. Vascular function, including perfusability and vascular barrier function, was characterized by beads loading and dextran diffusion, respectively. A computational atomistic simulation model was proposed to illustrate how solutes cross vascular lipid bilayer. The reported acoustofluidic methodology is capable of facile and reproducible fabrication of functional vessel network with specific geometry. It is promising to facilitate the development of both fundamental research and regenerative therapy.

Acoustic tweezers for high-throughput single-cell analysis

Acoustic tweezers provide an effective means for manipulating single cells and particles in a high-throughput, precise, selective and contact-free manner. The adoption of acoustic tweezers in next-generation cellular assays may advance our understanding of biological systems. Here we present a comprehensive set of instructions that guide users through device fabrication, instrumentation setup and data acquisition to study single cells with an experimental throughput that surpasses traditional methods, such as atomic force microscopy and micropipette aspiration, by several orders of magnitude. With acoustic tweezers, users can conduct versatile experiments that require the trapping, patterning, pairing and separation of single cells in a myriad of applications ranging across the biological and biomedical sciences. This procedure is widely generalizable and adaptable for investigations in materials and physical sciences, such as the spinning motion of colloids or the development of acoustic-based quantum simulations. Overall, the device fabrication requires ~12 h, the experimental setup of the acoustic tweezers requires 1-2 h and the cell manipulation experiment requires ~30 min to complete. Our protocol is suitable for use by interdisciplinary researchers in biology, medicine, engineering and physics.

In-vivo programmable acoustic manipulation of genetically engineered bacteria

Acoustic tweezers can control target movement through the momentum interaction between an acoustic wave and an object. This technology has advantages over optical tweezers for in-vivo cell manipulation due to its high tissue penetrability and strong acoustic radiation force. However, normal cells are difficult to acoustically manipulate because of their small size and the similarity between their acoustic impedance and that of the medium. In this study, we use the heterologous expression of gene clusters to generate genetically engineered bacteria that can produce numerous sub-micron gas vesicles in the bacterial cytoplasm. We show that the presence of the gas vesicles significantly enhances the acoustic sensitivity of the engineering bacteria, which can be manipulated by ultrasound. We find that by employing phased-array-based acoustic tweezers, the engineering bacteria can be trapped into clusters and manipulated in vitro and in vivo via electronically steered acoustic beams, enabling the counter flow or on-demand flow of these bacteria in the vasculature of live mice. Furthermore, we demonstrate that the aggregation efficiency of engineering bacteria in a tumour is improved by utilizing this technology. This study provides a platform for the in-vivo manipulation of live cells, which will promote the progress of cell-based biomedical applications.

Trends in mechanobiology guided tissue engineering and tools to study cell-substrate interactions: a brief review

Sensing the mechanical properties of the substrates or the matrix by the cells and the tissues, the subsequent downstream responses at the cellular, nuclear and epigenetic levels and the outcomes are beginning to get unraveled more recently. There have been various instances where researchers have established the underlying connection between the cellular mechanosignalling pathways and cellular physiology, cellular differentiation, and also tissue pathology. It has been now accepted that mechanosignalling, alone or in combination with classical pathways, could play a significant role in fate determination, development, and organization of cells and tissues. Furthermore, as mechanobiology is gaining traction, so do the various techniques to ponder and gain insights into the still unraveled pathways. This review would briefly discuss some of the interesting works wherein it has been shown that specific alteration of the mechanical properties of the substrates would lead to fate determination of stem cells into various differentiated cells such as osteoblasts, adipocytes, tenocytes, cardiomyocytes, and neurons, and how these properties are being utilized for the development of organoids. This review would also cover various techniques that have been developed and employed to explore the effects of mechanosignalling, including imaging of mechanosensing proteins, atomic force microscopy (AFM), quartz crystal microbalance with dissipation measurements (QCMD), traction force microscopy (TFM), microdevice arrays, Spatio-temporal image analysis, optical tweezer force measurements, mechanoscanning ion conductance microscopy (mSICM), acoustofluidic interferometric device (AID) and so forth. This review would provide insights to the researchers who work on exploiting various mechanical properties of substrates to control the cellular and tissue functions for tissue engineering and regenerative applications, and also will shed light on the advancements of various techniques that could be utilized to unravel the unknown in the field of cellular mechanobiology.

Fully Microfabricated Surface Acoustic Wave Tweezer for Collection of Submicron Particles and Human Blood Cells

Precise manipulation of (sub)micron particles is key for the preparation, enrichment, and quality control in many biomedical applications. Surface acoustic waves (SAW) hold tremendous promise for manipulation of (bio)particles at the micron to nanoscale ranges. In commonly used SAW tweezers, particle manipulation relies on the direct acoustic radiation effect whose superior performance fades rapidly when progressing from micron to nanoscale particles due to the increasing dominance of a second order mechanism, termed acoustic streaming. Through reproducible and high-precision realization of stiff microchannels to reliably actuate the microchannel cross-section, here we introduce an approach that allows the otherwise competing acoustic streaming to complement the acoustic radiation effect. The synergetic effect of both mechanisms markedly enhances the manipulation of nanoparticles, down to 200 nm particles, even at relatively large wavelength (300 μm). Besides spherical particles ranging from 0.1 to 3 μm, we show collections of cells mixed with different sizes and shapes inherently existing in blood including erythrocytes, leukocytes, and thrombocytes.

Sub-wavelength acoustic stencil for tailored micropatterning

Acoustofluidic devices are ideal for biomedical micromanipulation applications, with high biocompatibility and the ability to generate force gradients down to the scale of cells. However, complex and designed patterning at the microscale remains challenging. In this work we report an acoustofluidic approach to direct particles and cells within a structured surface in arbitrary configurations. Wells, trenches and cavities are embedded in this surface. Combined with a half-wavelength acoustic field, together these form an 'acoustic stencil' where arbitrary cell and particle arrangements can be reversibly generated. Here a bulk-wavemode lithium niobate resonator generates multiplexed parallel patterning via a multilayer resonant geometry, where cell-scale resolution is accomplished via structured sub-wavelength microfeatures. Uniquely, this permits simultaneous manipulation in a unidirectional, device-spanning single-node field across scalable ∼cm² areas in a microfluidic device. This approach is demonstrated via patterning of 5, 10 and 15 μm particles and 293-F cells in a variety of arrangements, where these activities are enabling for a range of cell studies and tissue engineering applications via the generation of highly complex and designed acoustic patterns at the microscale.

From rectangular to diamond shape: on the three-dimensional and size-dependent transformation of patterns formed by single particles trapped in microfluidic acoustic tweezers

Generally, the pattern formed by individual particles trapped inside a microfluidic chamber by a two-dimensional standing acoustic wave field has been considered only the result of the acoustic radiation force. Previous studies showed that particles can be trapped at the local minima and maxima of the first-order pressure and velocity fields. Thus, either a rectangular or a diamond pattern can be formed solely depending on the particle size, when the acoustic field is unchanged, and the material properties of the particles and the fluid are fixed. In this paper, we report about the co-existence of different patterns with particles of the same size. The actual shape of the patterns depends mainly on the ratio between particle diameter and wavelength. In addition, particles were found to be trapped at locations that coincide with the position of antinodes, even though the particles have a positive acoustic contrast factor. These phenomena imply that the trapping of individual particles cannot be described by the acoustic radiation force solely. Hence, further research is required, taking the viscous drag force caused by the fluid flow induced by the acoustic streaming effect into account.

Fortifying angiogenic efficacy of conditioned media using phototoxic-free blue light for wound healing

We used a blue organic light-emitting diode (bOLED) to increase the paracrine factors secreted from human adipose-derived stem cells (hADSCs) for producing conditioned medium (CM). Our results showed that while the bOLED irradiation promotes a mild-dose reactive oxygen generation that enhances the angiogenic paracrine secretion of hADSCs, it does not induce phototoxicity. The bOLED enhances paracrine factors via a cell-signaling mechanism involving hypoxia-inducible factor 1 alpha. This study demonstrated that the CM resulting from bOLED treatment shows improved therapeutic effects on mouse wound-healing models. This method contributes to overcoming the barriers to stem-cell therapies, including the toxicity and low yields from other methods such as nanoparticles, synthetic polymers, and even cell-derived vesicles.

Improvement of HEK293 Cell Growth by Adapting Hydrodynamic Stress and Predicting Cell Aggregate Size Distribution

HEK293 is a widely used cell line in the fields of research and industry. It is assumed that these cells are sensitive to hydrodynamic stress. The aim of this research was to use particle image velocimetry validated computational fluid dynamics (CFD) to determine the hydrodynamic stress in both shake flasks, with and without baffles, and in stirred Minifors 2 bioreactors to evaluate its effect on the growth and aggregate size distribution of HEK293 suspension cells. The HEK FreeStyle^TM 293-F cell line was cultivated in batch mode at different specific power inputs (from 63 W m-3 to 451 W m-3), whereby ≈60 W m-3 corresponds to the upper limit, which is what has been typically described in published experiments. In addition to the specific growth rate and maximum viable cell density VCDmax, the cell size distribution over time and cluster size distribution were investigated. The VCDmax of (5.77±0.02)·106cellsmL-1 was reached at a specific power input of 233 W m-3 and was 23.8% higher than the value obtained at 63 W m-3 and 7.2% higher than the value obtained at 451 W m-3. No significant change in the cell size distribution could be measured in the investigated range. It was shown that the cell cluster size distribution follows a strict geometric distribution whose free parameter p is linearly dependent on the mean Kolmogorov length scale. Based on the performed experiments, it has been shown that by using CFD-characterised bioreactors, the VCDmax can be increased and the cell aggregate rate can be precisely controlled.

Acoustic tweezers using bisymmetric coherent surface acoustic waves for dynamic and reconfigurable manipulation of particle multimers

HYPOTHESIS

The accurate and dynamic manipulation of multiple micro-sized objects has always been a technical challenge in areas of colloid assembly, tissue engineering, and organ regeneration. The hypothesis of this paper is the precise modulation and parallel manipulation of morphology of individual and multiple colloidal multimers can be achieved by customizing acoustic field.

EXPERIMENTS

Herein, we present a colloidal multimer manipulation method by using acoustic tweezers with bisymmetric coherent surface acoustic waves (SAWs), which enables contactless morphology modulation of individual colloidal multimers and patterning arrays by regulating the shape of acoustic field to specific desired distributions with high accuracy. Rapid switching of multimer patterning arrays, morphology modulation of individual multimers, and controllable rotation can be achieved by regulating coherent wave vector configurations and phase relations in real time.

FINDINGS

To demonstrate the capabilities of this technology, we have firstly achieved eleven patterns of deterministic morphology switching for single hexamer and precise switching between three array modes. In addition, the assembly of multimers with three kinds of specific widths and controllable rotation of single multimers and arrays were demonstrated from 0 to 22.4 rpm (tetramers). Therefore, this technique enables reversible assembly and dynamic manipulation of particles and/or cells in colloid synthesis applications.

Acousto-dielectric tweezers for size-insensitive manipulation and biophysical characterization of single cells

The intrinsic biophysical properties of cells, such as mechanical, acoustic, and electrical properties, are valuable indicators of a cell's function and state. However, traditional single-cell biophysical characterization methods are hindered by limited measurable properties, time-consuming procedures, and complex system setups. This study presents acousto-dielectric tweezers that leverage the balance between controllable acoustophoretic and dielectrophoretic forces applied on cells through surface acoustic waves and alternating current electric fields, respectively. Particularly, the balanced acoustophoretic and dielectrophoretic forces can trap cells at equilibrium positions independent of the cell size to differentiate between various cell-intrinsic mechanical, acoustic, and electrical properties. Experimental results show our mechanism has the potential for applications in single-cell analysis, size-insensitive cell separation, and cell phenotyping, which are all primarily based on cells' intrinsic biophysical properties. Our results also show the measured equilibrium position of a cell can inversely determine multiple biophysical properties, including membrane capacitance, cytoplasm conductivity, and acoustic contrast factor. With these features, our acousto-dielectric tweezing mechanism is a valuable addition to the resources available for biophysical property-based biological and medical research.

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.

Assessment of silicon, glass, FR4, PDMS and PMMA as a chip material for acoustic particle/cell manipulation in microfluidics

In the present study, the capabilities of different chip materials for acoustic particle manipulation have been assessed with the same microfluidic device architecture, under the same actuator and flow conditions. Silicon, glass, epoxy with fiberglass filling (FR4), polydimethylsiloxane (PDMS) and polymethyl methacrylate (PMMA) are considered as chip materials. The acoustophoretic chips in this study were manufactured with four different fabrication methods: plasma etching, chemical etching, micromachining and molding. A novel chip material, FR4, has been employed as a microfluidic chip material in acoustophoretic particle manipulation for the first time in literature, which combines the ease of manufacturing of polymer materials with improved acoustic performance. The acoustic particle manipulation performance is evaluated through acoustophoretic focusing experiments with 2μm and 12μm polystyrene microspheres and cultured breast cancer cell line (MDA-MB-231). Unlike the common approach in the literature, the piezoelectric materials were actuated with partitioned cross-polarized electrodes which allowed effective actuation of different family of chip materials. Different from previous studies, this study evaluates the performance of each acoustophoretic device through the perspective of synchronization of electrical, vibrational and acoustical resonances, considers the thermal performance of the chip materials with their effects on cell viability as well as manufacturability and scalability of their fabrication methods. We believe our study is an essential work towards the commercialization of acoustophoretic devices since it brings a critical understanding of the effect of chip material on device performance as well as the cost of achieving that performance.

Acoustofluidic assembly of primary tumor-derived organotypic cell clusters for rapid evaluation of cancer immunotherapy

Cancer immunotherapy shows promising potential for treating breast cancer. While patients may have heterogeneous treatment responses for adjuvant therapy, it is challenging to predict an individual patient's response to cancer immunotherapy. Here, we report primary tumor-derived organotypic cell clusters (POCCs) for rapid and reliable evaluation of cancer immunotherapy. By using a label-free, contactless, and highly biocompatible acoustofluidic method, hundreds of cell clusters could be assembled from patient primary breast tumor dissociation within 2 min. Through the incorporation of time-lapse living cell imaging, the POCCs could faithfully recapitulate the cancer-immune interaction dynamics as well as their response to checkpoint inhibitors. Superior to current tumor organoids that usually take more than two weeks to develop, the POCCs can be established and used for evaluation of cancer immunotherapy within 12 h. The POCCs can preserve the cell components from the primary tumor due to the short culture time. Moreover, the POCCs can be assembled with uniform fabricate size and cell composition and served as an open platform for manipulating cell composition and ratio under controlled treatment conditions with a short turnaround time. Thus, we provide a new method to identify potentially immunogenic breast tumors and test immunotherapy, promoting personalized cancer therapy.

Achieving Control in Micro-/Nanomotor Mobility

Unprecedented opportunities exist for the generation of advanced nanotechnologies based on synthetic micro/nanomotors (MNMs), such as active transport of medical agents or the removal of pollutants. In this regard, great efforts have been dedicated toward controlling MNM motion (e.g., speed, directionality). This was generally performed by precise engineering and optimizing of the motors' chassis, engine, powering mode (i.e., chemical or physical), and mechanism of motion. Recently, new insights have emerged to control motors mobility, mainly by the inclusion of different modes that drive propulsion. With high degree of synchronization, these modes work providing the required level of control. In this Minireview, we discuss the diverse factors that impact motion; these include MNM morphology, modes of mobility, and how control over motion was achieved. Moreover, we highlight the main limitations that need to be overcome so that such motion control can be translated into real applications.