Duke University engineers have developed a device that uses sound waves to separate and sort the smallest particles in blood in minutes. The technology is based on a concept called “virtual pillars” and could be a boon for both scientific research and medical applications.
Tiny biological nanoparticles called ‘small extracellular vesicles’ (sEVs) are released by every cell type in the body and are believed to play a major role in cell-to-cell communication and disease transmission. The new technology, called Acoustic Nanoscale Separation via Wave-pillar Excitation Resonance, or ANSWER for short, not only pulls these nanoparticles out of biofluids in less than 10 minutes, but also sorts them into size categories thought to have distinct biological roles.
The results appeared online November 23 in the Journal scientific advances.
“These nanoparticles have significant potential for medical diagnosis and treatment, but current technologies to separate and sort them take several hours or days, are inconsistent, produce low yield or purity, suffer from contamination, and sometimes damage the nanoparticles,” said Tony Jun Huang, William Bevan Distinguished Professor of Mechanical Engineering and Materials Science at Duke.
“We want to make extracting and sorting high-quality sEVs as easy as pressing a button and getting the samples you want faster than it takes to take a shower,” said Huang.
Recent research shows that sEVs consist of several subgroups with different sizes (e.g. smaller than 50 nanometers, between 60 and 80 nanometers and between 90 and 150 nanometers). Each size is believed to have different biological properties.
The recent discovery of sEV subpopulations has excited researchers for their potential to revolutionize the field of non-invasive diagnostics, such as early detection of cancer and Alzheimer’s disease. But the particles have not yet found their way to the clinic.
Huang said this is largely due to the difficulties involved in separating and isolating these nano-sized sEV subpopulations. To address this challenge, Huang, his graduate student Jinxin Zhang, and collaborators from UCLA, Harvard, and the Magee-Womens Research Institute developed the ANSWER platform.
The device uses a single pair of transducers to create a standing sound wave that envelops a narrow, enclosed, fluid-filled channel. The sound wave “leaks” through the channel walls into the liquid center and interacts with the original standing sound wave. With careful design of wall thickness, canal size and sound frequency, this interaction creates a resonance that forms “virtual columns” down the center of the canal.
Each of these virtual columns is essentially a semi-ovoid high pressure area. When particles try to cross the pillars, they are pushed to the edges of the channel. And the larger the particles, the greater the thrust. By tuning the series of virtual columns to produce nuanced forces on the migrating nanoparticles, the researchers can precisely size them into a variety of groups determined by the needs of the experiments at hand.
“ANSWER’s EV fractionation technology is the most advanced capability for precise EV fractionation and will significantly transform the horizons of EV diagnostics, prognosis and liquid biopsy,” said David Wong, director of the UCLA Center for Oral/Head & Neck Oncology Research.
In the new article, the researchers show that their ANSWER platform can successfully sort sEVs into three subgroups, with 96% accuracy for nanoparticles at the larger end of the spectrum and 80% accuracy for the smallest. They also show flexibility in their system, adjusting the number of groupings and size ranges with simple updates to the sound wave parameters. Each of the experiments lasted only 10 minutes, while other methods like ultracentrifugation can take several hours or days.
“Due to its non-contact nature, ANSWER offers a biocompatible approach to the separation of biological nanoparticles.” said Zhang. “Unlike mechanical filtering methods, which have fixed cutoff diameters, ANSWER provides a tunable approach to nanoscale separation, and the cutoff diameter can be precisely modified by varying the input acoustic power.”
In the future, researchers will continue to improve the ANSWER technology so that it can efficiently purify other biologically relevant nanoparticles such as viruses, antibodies and proteins.
This research was supported by the National Institutes of Health (UH3TR002978, R01HD103727, U18TR003778, R01GM132603, R01GM143439, R01GM135486, R01GM144417, R44AG063643) and the National Science Foundation (CMMI-2104295, CMMI-2104526).