Optimizing coupling layer and superstrate thickness in attachable acoustofluidic devices

Superstrate-based acoustofluidic devices, where the fluidic elements are reversibly coupled to a transducer rather than bonded to it, offer advantages for cost, interchangeability and preventing contamination between samples. A variety of coupling materials can be used to transmit acoustic energies into attachable superstrates, though the dimensions and material composition of the system elements are not typically optimized. This work analyzes these coupling layers for bulk wavefront transmission, including water, ultrasound gel and polydimethylsiloxane (PDMS), as well as the material makeup and thickness of the superstrate component, which is commonly comprised of glass, quartz or silicon. Our results highlight the importance of coupling layer and superstrate dimensions, identifying frequencies and component thicknesses that maximize transmission efficiency. Our results indicate that superstrate thicknesses 0.55 times the acoustic wavelength result in maximal acoustic coupling. While various coupling layers and superstrate materials are capable of similar acoustic energy transmission, the inherent dimensional stability of the PDMS coupling layers, somewhat less common in superstrate work compared to liquid-based agents, presents advantages for practically maximizing acoustic efficiency.

A Novel Detachable, Reusable, and Versatile Acoustic Tweezer Manipulation Platform for Biochemical Analysis and Detection Systems

Multifunctional, integrated, and reusable operating platforms are highly sought after in biochemical analysis and detection systems. In this study, we demonstrated a novel detachable, reusable acoustic tweezer manipulation platform that is flexible and versatile. The free interchangeability of different detachable microchannel devices on the acoustic tweezer platform was achieved by adding a waveguide layer (glass) and a coupling layer (polydimethylsiloxane (PDMS) polymer film). We designed and demonstrated the detachable multifunctional acoustic tweezer platform with three cell manipulation capabilities. In Demo I, the detachable acoustic tweezer platform is demonstrated to have the capability for parallel processing and enrichment of the sample. In Demo II, the detachable acoustic tweezer platform with capability for precise cell alignment is demonstrated. In Demo III, it was demonstrated that the detachable acoustic tweezer platform has the capability for the separation and purification of cells. Through experiments, our acoustic tweezer platform has good acoustic retention ability, reusability, and stability. More capabilities can be expanded in the future. It provides a simple, economical, and multifunctional reusable operating platform solution for biochemical analysis and detection systems.

Recent advances in acoustofluidic separation technology in biology

Acoustofluidic separation of cells and particles is an emerging technology that integrates acoustics and microfluidics. In the last decade, this technology has attracted significant attention due to its biocompatible, contactless, and label-free nature. It has been widely validated in the separation of cells and submicron bioparticles and shows great potential in different biological and biomedical applications. This review first introduces the theories and mechanisms of acoustofluidic separation. Then, various applications of this technology in the separation of biological particles such as cells, viruses, biomolecules, and exosomes are summarized. Finally, we discuss the challenges and future prospects of this field.

Nonprehensile Manipulation of Parts on a Horizontal Circularly Oscillating Platform with Dynamic Dry Friction Control

This paper presents a novel method for nonprehensile manipulation of parts on a circularly oscillating platform when the effective coefficient of dry friction between the part and the platform is being dynamically controlled. Theoretical and experimental analyses have been performed to validate the proposed method and to determine the control parameters that define the characteristics of the part’s motion. A mathematical model of the manipulation process with dynamic dry friction control was developed and solved. The modeling showed that by changing the phase shift between the function for dynamic dry friction control and the function defining the circular motion of the platform, the part can be moved in any direction as the angle of displacement can be controlled in a full range from 0 to 2π. The nature of the trajectory and the mean displacement velocity of the part mainly depend on the width of the rectangular function for dynamic dry friction control. To verify the theoretical findings, an experimental setup was developed, and experiments of manipulation were carried out. The experimental results qualitatively confirmed the theoretical findings. The presented analysis enriches the classical theories of nonprehensile manipulation on oscillating platforms, and the presented findings are relevant for mechatronics, robotics, mechanics, electronics, medical, and other industries.

Unconventional acoustic approaches for localized and designed micromanipulation

Acoustic fields are ideal for micromanipulation, being biocompatible and with force gradients approaching the scale of single cells. They have accordingly found use in a variety of microfluidic devices, including for microscale patterning, separation, and mixing. The bulk of work in acoustofluidics has been predicated on the formation of standing waves that form periodic nodal positions along which suspended particles and cells are aligned. An evolving range of applications, however, requires more targeted micromanipulation to create unique patterns and effects. To this end, recent work has made important advances in improving the flexibility with which acoustic fields can be applied, impressively demonstrating generating arbitrary arrangements of pressure fields, spatially localizing acoustic fields and selectively translating individual particles in ways that are not achievable via traditional approaches. In this critical review we categorize and examine these advances, each of which open the door to a wide range of applications in which single-cell fidelity and flexible micromanipulation are advantageous, including for tissue engineering, diagnostic devices, high-throughput sorting and microfabrication.

Low-cost laser-cut patterned chips for acoustic concentration of micro- to nanoparticles and cells by operating over a wide frequency range

Acoustofluidic platforms for cell manipulation benefit from being contactless and label-free at potentially low cost. Particle concentration in a droplet relies on augmenting spatial asymmetry in the acoustic field, which is difficult to reproduce reliably. Etching periodic patterns into a chip to create acoustic band gaps is an attractive approach to spatially modify the acoustic field. However, the sensitivity of acoustic band structures to geometrical tolerances requires the use of costly microfabrication processes. In this work, we demonstrate particle concentration across a range of periodic structure patterns fabricated with a laser-cutting tool, suitable for low-cost and low-volume rapid prototyping. The relaxation on precision is underscored by experimental results of equally efficient particle concentration outside band gaps and even in their absence, allowing operation over a range of frequencies independent of acoustic band gaps. These results are significant by indicating the potential of extending the proposed method from the microscale (e.g. tumor cells) to the nanoscale (e.g. bacteria) by scaling up the frequency without being limited by fabrication capabilities. We demonstrate the device's high degree of biocompatibility to illustrate the method's applicability in the biomedical field for applications such as basic biochemical analysis and in vitro diagnosis.