Small transducers to investigate ultrasound-cellular interactions

Christina Hendren

The small transducers and driving systems to investigate ultrasound-cell and tissue interactions project combines techniques from the Xu Lab and the Deng Lab. This involves designing, building, and testing high frequency (1-5 MHz) transducers which are custom made for three applications, requiring a range of skills including hands-on experimentation and computer-based design and analysis. The first application is resonant acoustic rheometry (RAR), a technique which was created to perform non-contact, dynamic, low-volume materials testing. RAR uses a single transducer to transmit a “pushing” pulse which creates miniscule displacement of a liquid or soft material surface and then to receive the reflection from that interface. The frequency spectrum of these responses contains information about the sample’s shear modulus and surface tension. The complex waveforms used to control the transducer in this application required a custom driver circuit which was designed to be universally capable of driving all transducers of the project. The second application is acoustic tweezing cytometry (ATC), which relies on bubbles to transmit acoustic forces to cells without causing damage. The functionalized lipid microbubbles are attached to specific cellular structures, then ultrasound is applied over time to provide cyclic mechanical stimulation. This technique thus utilizes mechanobiology and is of most interest for accelerating the differentiation process of embryonic stem cells. The third application is histotripsy under the microscope, which will be performed to investigate the mechanism by which mechanical cavitation ablates tissue and interacts with cells. To create the desired small, dense cavitation cloud, high frequency and “microtripsy”-style pulses (meaning the pressure is just above the intrinsic threshold) will be used. Observing the histotripsy process on the microscale (on the order of hundreds of micrometers) is exciting because it can provide important information which will shape improved histotripsy therapy.