Microfluidic devices are commonly used to separate and sort platelets, red and white blood cells, tumor cells in blood and other components found in fluids in order to understand diseases and develop treatments. While this and other technologies developed in research labs are sufficient for this purpose, they do not perform well enough for use in clinical and industrial settings. A new approach uses a living organism for real-time measurement and monitoring of acoustic microfluidic device performance.

“The goal of this work is to use these cells to characterize the acoustic field, to find resonances and to assess field strength, and eventually to calibrate device performance using the cells as our measurement tool,” said Mark Meacham, assistant professor of mechanical engineering and materials science in the McKelvey School of Engineering, University of Washington in St. Louis. “We know how much power is put Living cells are used for real-time measurement and monitoring of acoustic microfluidic device performance. Source: Washington University in St. Louis.in. The cells give us a way to evaluate how much of that power is useful.”

The efficacy of the bulk acoustic wave devices designed by the researchers was tested with Chlamydomonas reinhardtii, a single-cell green alga that swims with two whip-like structures called cilia. These cells have a fairly uniform size and swimming speed (approximately 100 micrometers per second) and naturally spread themselves evenly throughout the chamber of a microfluidic device in seconds.

The active cells used in this approach replaced the typically used passive polystyrene beads. The beads require a tedious process that does not yield real-time information.

The devices translate an electrical signal to mechanical vibrations using piezoelectric materials and generate ultrasonic standing waves in the fluid-filled channel. The microfluidic tool is designed to operate at multiple resonant frequencies to generate strong acoustic waves with maximum energy transfer. Efficiency is critical to prevent the devices from generating heat that can kill biological cells.

The approach was first demonstrated on a straight microchannel and circular chamber and then on a more complex device with a microfluidic chamber consisting of two different domains. The swimming cells continuously responded to the changing acoustic field and were able to distinguish between the various resonances of the chamber. When the scientists turned on the acoustic radiation force, the algae cells became trapped tightly together in low-pressure regions of the chamber. Varying the frequency of operation causes the cells to collect into different shapes based on the shape of the channel. When the force is removed, they once again swim naturally.

“These living cells make for a very effective measurement tool to investigate acoustic forces,” Meacham said. “They are also easy to culture and don’t need a lot of specialized equipment like animal cells, just a box with a light at room temperature.”

A paper on the research is published in Lab on a Chip.