A novel acoustofluidic platform for enhanced microstreaming and chaotic flow in single-phase and droplet microfluidics

Abstract

Microfluidics has transformed the landscape of biomedical and chemical re search by enabling precise control over small fluid volumes, facilitating rapid mix ing, particle manipulation, and reagent economy in lab-on-a-chip systems. How ever, achieving efficient mixing and tunable reaction conditions within microchan nels remains a persistent challenge due to the laminar flow regime that dominates at these scales. To overcome these limitations, acoustofluidics—an emerging field that harnesses acoustic forces to manipulate fluids and particles—offers a power ful, contactless strategy for enhancing microscale operations. This thesis presents the development of novel acoustofluidic platforms tai lored for diverse biological and chemical applications, with an emphasis on li posome synthesis, flow control, and particle-based assays. In the first study, a high-efficiency liposome synthesis method is demonstrated using a sharp-edged acoustofluidic micromixer. By introducing glycerol into the aqueous phase, the size of liposomes can be precisely controlled, and by adjusting the glycerol per centage, size-tunable vesicles with improved dispersity are obtained. In the second study, a novel acoustofluidic platform is developed that combines an oscillating thin elastic membrane with vibrating trapped air bubbles to gener ate enhanced acoustic streaming. The working principle and mixing mechanism are examined both numerically and experimentally, with simulations guiding the optimization of structural parameters and predicting internal flow patterns. The device achieves exceptional mixing performance for both aqueous and viscous so lutions at flow rates up to 8000 µL/h, enabling high-throughput production of monodisperse lipid nanoparticles using both solvent-based and solvent-free meth ods. This high mixing efficiency also prevents nanoparticle aggregation, making the platform uniquely suited for synthesizing monodisperse liposomes. As a proof of concept, the effects of phospholipid type and concentration, flow rate, and glycerol content are systematically investigated, revealing a dramatic reduction in liposome size—from approximately 900 nm to 40 nm—by simply introducing 75% glycerol into the reagents. The simplicity of fabrication and operation, com bined with rapid mixing and intense agitation, positions this device as a versatile and indispensable acoustofluidic tool for nanoparticle and lipid nanoparticle pro duction, offering fine control over synthesis outcomes. In the final study, a pulsatile acoustofluidic platform is introduced to induce chaotic advection in both single-phase and droplet-based (multiphase) microflu idic systems via controlled acoustic excitation cycles. By tuning the frequency and duration of acoustic pulses, dynamic flow modulation is achieved, transition ing between laminar and chaotic regimes. This enhances mixing efficiency, droplet homogenization, and particle manipulation within confined microscale volumes. Beyond flow control, the platform is applied to a fluorescence-based protein–drug binding assay (RB–BSA interaction), where pulsatile actuation markedly im proves binding kinetics. Cell viability analysis using MCF-7 cells further confirms the system’s compatibility with biological samples. Together, these platforms demonstrate the versatility and adaptability of acoustofluidic systems for advanced microscale applications, offering scalable, tunable, and biocompatible solutions for nanoparticle synthesis, biochemical pro cessing, and droplet-based manipulation.