Sub-wavelength acoustic stencil for tailored micropatterning

Optoelectronic Tweezers Micro-Well System for Highly Efficient Single-Cell Trapping, Dynamic Sorting, and Retrieval

Single-cell arrays have emerged as a versatile method for executing single-cell manipulations across an array of biological applications. In this paper, an innovative microfluidic platform is unveiled that utilizes optoelectronic tweezers (OETs) to array and sort individual cells at a flow rate of 20 µL min-1. This platform is also adept at executing dielectrophoresis (DEP)-based, light-guided single-cell retrievals from designated micro-wells. This presents a compelling non-contact method for the rapid and straightforward sorting of cells that are hard to distinguish. Within this system, cells are individually confined to micro-wells, achieving an impressive high single-cell capture rate exceeding 91.9%. The roles of illuminating patterns, flow velocities, and applied electrical voltages are delved into in enhancing the single-cell capture rate. By integrating the OET system with the micro-well arrays, the device showcases adaptability and a plethora of functions. It can concurrently trap and segregate specific cells, guided by their dielectric signatures. Experimental results, derived from a mixed sample of HepG2 and L-O2 cells, reveal a sorting accuracy for L-O2 cells surpassing 91%. Fluorescence markers allow for the identification of sequestered, fluorescence-tagged HepG2 cells, which can subsequently be selectively released within the chip. This platform's rapidity in capturing and releasing individual cells augments its potential for future biological research and applications.

Micro-Acoustic Holograms for Detachable Microfluidic Devices

Acoustic microfluidic devices have advantages for diagnostic applications, therapeutic solutions, and fundamental research due to their contactless operation, simple design, and biocompatibility. However, most acoustofluidic approaches are limited to forming simple and fixed acoustic patterns, or have limited resolution. In this study,a detachable microfluidic device is demonstrated employing miniature acoustic holograms to create reconfigurable, flexible, and high-resolution acoustic fields in microfluidic channels, where the introduction of a solid coupling layer makes these holograms easy to fabricate and integrate. The application of this method to generate flexible acoustic fields, including shapes, characters, and arbitrarily rotated patterns, within microfluidic channels, is demonstrated.

Enhanced acoustic streaming effects via sharp-edged 3D microstructures

Acoustofluidic micromanipulation is an important tool for biomedical research, where acoustic forces offer the ability to manipulate fluids, cells, and particles in a rapid, biocompatible, and contact-free manner. Of particular interest is the investigation of acoustically driven sharp edges, where high tip velocity magnitudes and strong acoustic potential gradients drive rapid motion. Whereas prior devices utilizing 2D sharp edges have demonstrated promise for micromanipulation activities, taking advantage of 3D structures has the potential to increase their performance and the range of manipulation activities. In this work, we investigate high-magnitude acoustic streaming fields in the vicinity of sharp-edged, sub-wavelength 3D microstructures. We numerically model and experimentally demonstrate this in fabricating parametrically configured 3D microstructures whose tip-angle and geometry influence acoustic streaming velocities and the complexity of streaming vortices, finding that the simulated and realized velocities and streaming patterns are both tunable and a function of microstructure shape. These sharp-edge interfaces hold promise for biomedical studies benefiting from precise and targeted micromanipulation.

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.