CAREER: Dynamic characterization of acoustofluidic devices using living probes

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Acoustofluidics is the use of sound waves to manipulate small objects or particles in liquids. Acoustic microfluidic devices have great potential for applications in medicine and biology because ultrasound, which is known to be safe, can be used to move tiny objects without touching them. These objects can range in size from individual molecules to biological cells. However, the use of acoustofluidic devices has been limited by an inability to measure and compare their performance to ensure consistent quality. This CAREER project will use active, swimming algae cells to assess how well acoustofluidic devices work. The ability of swimming microorganisms to respond to their changing environment will be exploited to see and measure ultrasound waves in devices with complicated shapes. This new measurement approach can be used to streamline testing of acoustic microfluidic devices for mixing, separation, trapping, and controlled motion of microscopic objects. The study of sound waves also presents a unique opportunity to engage and excite students and the general public through their basic understanding and natural interest in sound. The CAREER project will support the development of activities to teach about waves, sound, and vibrations at Washington University and in the St. Louis region. Undergraduate researchers and teacher interns will design, make, and test acoustic microfluidic devices, and create educational materials for K-12 students. Videos, demonstrations, and teaching modules will be used at local schools, providing opportunities to engage underrepresented students in STEM. Educational activities on these topics will be incorporated into the university's Institute for School Partnership MySci program, which reaches approximately 100,000 K-12 students and is integral to regional STEM education.Inadequate metrology is a critical barrier to the translation of acoustofluidics from the laboratory into practice. However quantitative prediction of acoustofluidic parameter fields (force, force potential, and pressure) is challenging, as idealized computational models fail to accurately capture the complexity of real devices (e.g., manufacturing tolerances and component interfaces). In addition, current experimental methods are limited to simple geometries and rely on passive tracer particles that cannot respond to the changing field as conditions vary. The goal of the CAREER project is to use the interactions of swimming cells with ultrasonic standing waves to elucidate and quantify the performance of complex acoustofluidic devices. Cells of the alga C. reinhardtii continuously probe their environment, yielding a comprehensive, real-time picture of the acoustic field throughout the fluid domain. By calibrating these micro-swimmers (i.e., establishing their acoustophysical properties and propulsive capability), the dynamic evolution of their spatial distribution can be correlated to the evolving field shape. This technique can be used to characterize performance and identify optimal operating conditions. Conversely, these field-particle interactions will provide opportunities to investigate how micro-swimmers respond to external force fields. Accurate and rapid performance characterization is critical to the advancement of acoustofluidics, and thus the CAREER project will accelerate realization of the full potential of these technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.