Acoustophoresis in polymer-based microfluidic devices: Modeling and experimental validation

Abstract

A finite-element model is presented for numerical simulation in three dimensions of acoustophoresis of suspended microparticles in a microchannel embedded in a polymer chip and driven by an attached piezoelectric transducer at MHz frequencies. In accordance with the recently introduced principle of whole-system ultrasound resonances, an optimal resonance mode is identified that is related to an acoustic resonance of the combined transducer-chip-channel system and not to the conventional pressure half-wave resonance of the microchannel. The acoustophoretic action in the microchannel is of comparable quality and strength to conventional silicon-glass or pure glass devices. The numerical predictions are validated by acoustic focusing experiments on 5-μm-diameter polystyrene particles suspended inside a microchannel, which was milled into a polymethylmethacrylate chip. The system was driven anti-symmetrically by a piezoelectric transducer, driven by a 30-V peak-to-peak alternating voltage in the range from 0.5 to 2.5 MHz, leading to acoustic energy densities of 13 J/m3 and particle focusing times of 6.6 s.

Microfluidics for Multiphase Mixing and Liposomal Encapsulation of Nanobioconjugates: Passive vs. Acoustic Systems

“…where σ is the stress tensor, P is the pressure, u is the velocity, q is the heat from the thermoviscous effect, T is the temperature, µ B is the bulk viscosity, µ is the dynamic viscosity, and I is the intensity vector, which is defined as the time average of the instantaneous rate of energy per unit area by Equation (28).…”

“…For liposome encapsulation, conventional methods (e.g., rehydration of phospholipids in the presence of an aqueous suspension of the nanostructured material) lead to low encapsulation efficiencies and high polydispersity indexes as the process proceeds in an uncontrolled manner [3]. However, acoustofluidics has shown to be an efficient avenue for increasing mixing and enhancing the manipulation of particles suspended in fluids within microfluidic devices, by using integrated transducers and piezoelectric components aided by frequencies of up to 2 MHz [25][26][27][28][29]. For instance, with the aid of acoustic streaming and radiation forces in a cell-nanoparticle mixture, fluid-particle interactions are favored for reaching high cell uptakes [30,31].…”

Theory and modeling of nonperturbative effects at high acoustic energy densities in thermoviscous acoustofluidics

“…For simplicity, the piezoelectric transducer is left out of the analysis, and is only represented by an oscillating displacement condition on part of the surface of the elastic solid. We have in other studies included a full model of the transducer in the numerical model [6,16,17].…”

Numerical study of acoustic cell trapping above elastic membrane disks driven in higher-harmonic modes by thin-film transducers with patterned electrodes

“…The basic theory and modeling for such a thin-film PZE-transducer-driven acoustofluidic system, was developed in a perturbation scheme involving the acoustic first-order fields and the steady time-averaged secondorder fields in our previous work [3], founded on the theory for bulk PZE-transducer-driven systems [22] taking the acoustic boundary layers into account analytically through effective boundary conditions [23]. Numerical simulations based on this theory have been validated experimentally for several different microscale acoustofluidic systems [2,9,10,22]. In the following we briefly summarize this basic theory and its numerical implementation and adapt the previous cartesian-coordinate formulation into the cylindrical coordinates of the present axisymmetric system.…”

“…However, when dealing with bulk acoustic waves (BAW), the topic of this work, electrode shaping is rarely used, and not at all for the above-mentioned membrane devices. A simple split-electrode configuration with an applied anti-symmetric driving voltage, has been used on experiments on bulk piezoelectric (PZE) transducers [9,10] and on thin-film transducers [1] to obtain a strong excitation of anti-symmetric modes for optimal particle focusing. Such systems has also been studied in numerical simulations [3,[11][12][13].…”