Surface acoustic wave microfluidics: device innovations and the triangle balance in micro /nanoscale manipulation

Micro/Nanoscale Acoustic Manipulation: From Particle Control to Autonomous Microswimmers

ABSTRACT Acoustic manipulation and propulsion technologies have emerged as powerful platforms for micro/nanoscale control, enabled by their non‐contact operation, label‐free compatibility, biocompatibility, and strong penetration capability. This review systematically examines the physical mechanisms and recent advances in acoustically enabled passive particle manipulation and autonomous microswimmer propulsion. First, this article outlines the generation and propagation of acoustic waves and their fundamental interactions with matter, with emphasis on acoustic radiation forces and acoustic streaming. It then classifies representative device architectures and acoustic field modulation strategies based on bulk acoustic wave and surface acoustic wave systems. Building on this framework, recent progress in precise target manipulation across diverse media is synthesized, encompassing trapping, transport, enrichment, separation, and patterning. Furthermore, the review highlights the rapidly evolving field of acoustically driven microswimmers, analyzing autonomous propulsion mechanisms arising from shape‐ and density‐induced asymmetries, cavitation phenomena, and sharp‐edge oscillations, as well as recent advances in collective behavior, swarm coordination, and intelligent navigation. By delineating the developmental trajectory and key challenges of acoustic manipulation and propulsion, this review establishes a comprehensive knowledge framework for interdisciplinary researchers and highlights future opportunities in precision medicine, smart materials, micro/nano‐fabrication, and cross‐scale biological manipulation.

Acoustic virtual walls enable open, scalable, and programmable microfluidics

Microfluidic platforms are widely used across biomedical research, chemical synthesis, diagnostics, environmental monitoring, and materials science for precisely manipulating small volumes of fluids and suspended particles. However, conventional systems rely on narrow physical channels that are prone to clogging, limited volumetric throughput due to high hydraulic resistance, and excessive shear stress that can damage sensitive cells and fragile materials. To overcome these constraints, we introduce acoustic channeling within a wide, open fluid chamber by replacing solid boundaries with acoustic virtual walls. These walls are formed by evanescent acoustic pressure fields generated from an engineered two-dimensional waveguide that suppresses internal wave propagation and produces highly localized subwavelength fields. This architecture minimizes shear stress while guiding particles along precisely defined trajectories. The electronically tunable acoustic field enables programmable, remote, and real-time particle control. Supported by simulations, we demonstrate diverse channeling designs, efficient particle collection, and material-specific separation. Operating at milliliter-per-minute flow rates, two orders of magnitude higher than conventional microfluidic systems, this platform enables scalable, clog-free microfluidics for high-throughput and robust applications.

Accurate Control of Microspheres by Surface Acoustic Waves for Quantitative Force Characterization and Cell Mechanics Measurement.

The mechanical properties of cells are critical indicators of cellular physiological state and function. However, existing technologies still face challenges in achieving non-contact, force-calibrated, and precisely controlled single-probe measurements of single-cell mechanical properties. A phase-programmable surface acoustic wave (SAW) platform is presented, in which orthogonally arranged interdigitated transducers (IDTs) generate controllable acoustic fields for deterministic two-dimensional manipulation of microspheres. Dynamic phase modulation of the SAW fields enables high-precision microsphere steering while producing tunable acoustic radiation forces in the piconewton-nanonewton range. To enable direct quantitative characterization of acoustic forces, a calibrated microneedle-microsphere force probe is integrated into the platform. This configuration establishes an experimental phase-force relationship, enabling in situ calibration of acoustic radiation forces without relying on theoretical models or indirect calculation. Based on this experimentally calibrated acoustic force framework, SAW-driven 5 μm microspheres are employed as localized single probes to perform controlled acoustic indentation of adherent C2C12 myoblasts. The apparent Young's modulus is determined to be 1.63 ± 0.21 kPa using Hertzian contact mechanics and shows agreement with AFM-based measurements under comparable experimental conditions. c Overall, this work establishes a calibrated acoustic radiation force measurement and single-cell apparent Young's modulus characterization approach. This approach may have potential significance for non-contact mechanophenotyping and lab-on-chip based cell mechanics studies. STATEMENT OF SIGNIFICANCE: R2: Accurate single-cell mechanical characterization is limited by the lack of direct force calibration and controllable acoustic loading in SAW-based techniques. In this work, we implemented a phase-programmable SAW platform that enables deterministic microsphere manipulation and controllable acoustic force generation. By integrating a calibrated microneedle-microsphere probe, we established a direct phase-force relationship, enabling in situ and direct measurement of acoustic radiation forces and overcoming reliance on theoretical or indirect force estimation. This calibrated acoustic manipulation framework further enables controlled probe-based indentation of adherent cells and quantitative determination of their apparent Young's modulus. The proposed work may advance acoustic force-based mechanophenotyping and provide a promising pathway toward scalable, chip-integrated single-cell mechanical analysis.

Optimization of Serpentine Microfluidic Chip Integrated by Sharp-Corner-Based Microstructure

This study presents a systematic optimization of sharp-corner microstructures integrated into a "Christmastree" architecture to overcome diffusion-limited mass transport in low-Reynolds-number regimes, enabling rapid and homogeneous mixing within complex branching networks for high-throughput microfluidic gradient generators. Through a bidirectional co-simulation workflow between SolidWorks and COMSOL Multiphysics, we map the non-linear coupling between geometric parameters, i.e., the sharp-corner width and height, and the resulting mixing performance. Analysis of the global design space reveals a multi-peaked landscape, facilitating critical distinction between physically viable structural optima and numerical "pseudo-optima" plagued by deleterious flow separation and stagnant dead zones. The structural optimum is identified at a height of 0.16 mm and a width of 0.1 mm, where induced transverse secondary flows maximize concentration homogenization while preserving hydrodynamic integrity. This study provides a robust methodological reference for the automated design of passive microfluidic modules, ensuring reliable gradient generation for next-generation lab-on-a-chip applications.

An integrated platform for metamaterial-based sensing and surface acoustic wave-based acoustofluidics utilising circular interdigital transducers

Capillary Microfluidics for Bioanalysis: Design Principles and Application Perspectives.

Capillary flow-driven microfluidic devices enable autonomous fluid transport for bioanalytical applications by using surface tension and wettability in microscale channels and porous structures, eliminating the need for external pumps. This review develops a coherent physical framework for capillary devices, based on the Young-Laplace equation, Jurin's law, the Lucas-Washburn equation, and Darcy's law, that relates interfacial curvature, capillary pressure, viscous dissipation, and permeability to fluid behavior in both hollow channels and porous media. From this framework, we derive practical design principles for priming, timing, valving, and sample metering in paper-based, laminate, and hybrid devices and demonstrate how these principles enable autonomous bioanalytical functions, including plasma separation, nucleic acid extraction, analyte preconcentration, immunoassays, and nucleic acid tests in both lithographically fabricated and paper-based platforms. The review places strong emphasis on mechanistic design rules that link capillary physics to assay performance, reproducibility, and integration level, reduce user intervention, shorten assay time, and approach laboratory-grade analytical performance while preserving low cost and portability. Finally, we discuss emerging wearable and body-interfaced devices that integrate capillary-driven sampling of sweat, interstitial fluid, and other biofluids with colorimetric, electrochemical, and optical readouts for continuous or time-resolved measurements. Together, these developments show how capillary actuation, grounded in classical transport laws, is enabling increasingly sophisticated pump-free microfluidic systems that are well suited to decentralized diagnostics, environmental monitoring, and point-of-need bioanalysis.