Simple and inexpensive micromachined aluminum microfluidic devices for acoustic focusing of particles and cells

Abstract

We introduce a new method to construct microfluidic devices especially useful for bulk acoustic wave (BAW)-based manipulation of cells and microparticles. To obtain efficient acoustic focusing, BAW devices require materials that have high acoustic impedance mismatch relative to the medium in which the cells/microparticles are suspended and materials with a high-quality factor. To date, silicon and glass have been the materials of choice for BAW-based acoustofluidic channel fabrication. Silicon- and glass-based fabrication is typically performed in clean room facilities, generates hazardous waste, and can take several hours to complete the microfabrication. To address some of the drawbacks in fabricating conventional BAW devices, we explored a new approach by micromachining microfluidic channels in aluminum substrates. Additionally, we demonstrate plasma bonding of poly(dimethylsiloxane) (PDMS) onto micromachined aluminum substrates. Our goal was to achieve an approach that is both low cost and effective in BAW applications. To this end, we micromachined aluminum 6061 plates and enclosed the systems with a thin PDMS cover layer. These aluminum/PDMS hybrid microfluidic devices use inexpensive materials and are simply constructed outside a clean room environment. Moreover, these devices demonstrate effectiveness in BAW applications as demonstrated by efficient acoustic focusing of polystyrene microspheres, bovine red blood cells, and Jurkat cells and the generation of multiple focused streams in flow-through systems. Graphical abstract The aluminum acoustofluidic device and the generation of multinode focusing of particles.

Whole-System Ultrasound Resonances as the Basis for Acoustophoresis in All-Polymer Microfluidic Devices

“…Both methods are actively being used in contemporary acoustofluidics as is evident from the following examples published in the literature the past two years. BAW devices have been used for cell focusing in simple and inexpensive aluminum devices [20], for binary particle separation in droplet microfluidics [21], for hematocrit determination [22], for enrichment of tumor cells from blood [23], and for manipulation of C. elegans [24,25], while SAW devices have been used for nanoparticle separation [26,27], for self-aligned particle focusing and patterning [28], for enhanced cell sorting [29], and for in-droplet microparticle separation [30]. Currently, the acoustofluidic devices with the highest throughput are of the BAW type [5].…”

Microparticle Acoustophoresis in Aluminum-Based Acoustofluidic Devices with PDMS Covers

“…This device geometry is similar to the one in Ref. [20], namely an aluminum-based device with a straight channel and a single PDMS cover. Our general numerical modeling is then validated experimentally for this device and further supported by the results presented in Section 4, for the anti-symmetric actuated design.…”

“…Also Xu et al, used such a glass-PDMS-glass structure in their recent device for isolation of cells from dilute samples using bead-assisted acoustic trapping [19]. Similarly in 2018, Gautam et al, designed, fabricated, and tested simple and inexpensive micromachined PDMS-covered aluminum-based microfluidic devices for acoustic focusing of particles and cells [20]. These devices appear to be versatile and truly simple to fabricate, as the desired microchannel system is micromilled into the surface of an aluminum base and bonded with a PDMS cover.…”

“…These devices appear to be versatile and truly simple to fabricate, as the desired microchannel system is micromilled into the surface of an aluminum base and bonded with a PDMS cover. Since neither theory nor simulation was presented by Gautam et al [20], we develop in this work a numerical model for such devices and validate them experimentally: In Section 3 for a basic design similar to that in Ref. [20], where a microchannel is micromilled into the surface of an aluminum base and sealed with a PDMS cover as sketched in Figure 1 and with the dimensions given in Table 1; and in Section 4 for a geometrically symmetric, but anti-symmetrically ac-voltage-actuated device.…”

Fabrication of Silicon Microfluidic Chips for Acoustic Particle Focusing Using Direct Laser Writing

“…The higher actuation voltage results in a higher temperature rise in the chip and therefore efficient cooling systems need to be integrated, which complicates the experimental setup. There are also a few reports on bulk acoustic wave devices fabricated in metals such as aluminium and stainless steel [11,12]. However, as of today silicon and glass are still the most commonly used materials for bulk acoustic wave devices.…”