Polymer-based acoustofluidics: bridging simulation and experiment

Acoustofluidics is an interdisciplinary field involving acoustics and microfluidics. Acoustofluidic applications utilize the acoustic radiation force for label-free and gentle manipulation of particles. The label-free and gentle manipulation make the acoustofluidic technology suitable for biomedical applications. As acoustofluidic technology has matured throughout the last three decades, commercial interest has grown.
Typically, an acoustofluidic device is fabricated in silicon and glass using clean-room techniques, but as companies try to commercialize the technology, alternative and costefficient fabrication methods are desired, e.g., injection molded or 3D printed polymer devices. However, designing polymer-based acoustofluidic devices is not a straightforward procedure. Due to the low acoustic contrast between polymers and fluids, the design principles from clean-room fabricated silicon and glass-based devices are no longer applicable. Furthermore, the acoustic response in a polymer-based device is weakened due to the leakage and attenuation of acoustic waves. Therefore, polymer-based acoustofluidic devices require optimization to be competitive. Computer-aided device engineering can be used to efficiently test and optimize device designs; doing so requires accurate modeling.
In this thesis, our recently developed UEIS method will be used to determine complex-valued material parameters of different classes, including piezoceramics, a UV-curable adhesive, a polymer, and a 3D-print resin. The UEIS method provides a low-cost, easy-to-execute method that only requires simple equipment. The UEIS method is verified by ultrasound-through transmission and laser-Doppler velocimetry. The UEIS-determined material parameters enable precise and accurate modeling of polymer-based acoustofluidic devices allowing computer-aided device optimization and accurate 3D-print prototyping. Furthermore, we have developed a numerical model able to simulate acoustofluidic phenomena in multiphysics and complex systems, including the transducer, the coupling layer, and the fluid-filled microfluidic chip. The model capability is illustrated as we present simulations of polymer-based acoustofluidic devices, including the calculation of particle trajectories influenced by acoustic forces in continuous and stop-flow conditions. The particle trajectories are compared to experimental tracks providing a frequency-resolved one-to-one comparison between experiment and simulation without free parameters, i.e., an attempt to bridge simulation and experiment. I hope this thesis will provide insight into the challenges and possibilities within the field of polymer-based acoustofluidics.