Quantitative Acoustophoresis

Abstract

Studying cellular mechanics allows important insights into its cytoskeletal composition, developmental stage, and health. While many force spectroscopy assays exist that allow probing of mechanics of bioparticles, most of them require immobilization of and direct contact with the particle and can only measure a single particle at a time. Here, we introduce quantitative acoustophoresis (QAP) as a simple alternative that uses an acoustic standing wave field to directly determine cellular compressibility and density of many cells simultaneously in a contact-free manner. First, using polymeric spheres of different sizes and materials, we verify that our assay data follow the standard acoustic theory with great accuracy. We furthermore verify that our technique not only is able to measure compressibilities of living cells but can also sense an artificial cytoskeleton inside a biomimetic vesicle. We finally provide a thorough discussion about the expected accuracy our approach provides. To conclude, we show that compared to existing methods, our QAP assay provides a simple yet powerful alternative to study the mechanics of biological and biomimetic particles.

Viscoelasticity of diverse biological samples quantified by Acoustic Force Microrheology (AFMR)

“…The acoustic field always displays some local heterogeneity in strength, which we did not correct for in the current measurements. It has previously been shown that for samples having similar compressibility as water (such as cells or diluted gels), such correction does not significantly impact average values 43 . In addition, potential heterogeneity in acoustic field is not expected to affect parameters such as power-law exponents (see Methods).…”

“…Since microrheology uniquely allows the study of viscoelastic heterogeneities within an assembled network 49 , 52 , we investigated the variance of viscoelastic parameters for the two different collagen concentrations. Here, we focused again on the frequency dependence of the viscous modulus, also since this value is not influenced by the local heterogeneity of the acoustic field 42 , 43 (see “Methods”). Nevertheless, in order to better appreciate the sample heterogeneity, this time we considered the frequency dependence of G” for each bead individually.…”

Microparticles with tunable, cell-like properties for quantitative acoustic mechanophenotyping

“…Garofalo et al calculated the compressibility of leukocytes using density values reported earlier 26 along with the measured acoustic separation of a mixed suspension of reference polystyrene microparticles and cells 28 . Bogatyr et al measured the size, density, and compressibility of individual microparticles and two cell lines by tracking gravitational settling in addition to acoustophoresis within a static acoustic chamber 29 . Similarly, Bellebon et al measured the gravitation settling and acoustophoretic migration of individual mesenchymal stromal cells to measure their size, density, and compressibility within a closed acoustic cavity 30 .…”

“…Similarly, Bellebon et al measured the gravitation settling and acoustophoretic migration of individual mesenchymal stromal cells to measure their size, density, and compressibility within a closed acoustic cavity 30 . While this method provides quantitative measurements of all three cell properties and is useful for studying temporal cellular physical alterations, it suffers from low throughput, ~1.3 cells/s 29 and ~1 cell/min 30 , due to settling times and low cell concentration within the field of view to allow for tracking of individual cells; moreover, it is not in continuous flow, limiting its utility for larger samples. In comparison to these studies, this work achieved a throughput of >500 cells/s in continuous flow with a single low viscosity fluid; however it has the drawback that assumptions of average size limited the accuracy.…”

Integrated Microfluidics for Single‐Cell Separation and On‐Chip Analysis: Novel Applications and Recent Advances

“…[176][177][178][179] Furthermore, acoustophoresis has emerged as a powerful and versatile tool that can help enable high-throughput mechanical analyses. [180] Morales et al effectively merged acoustic wave techniques to manipulate cells and optical interferometry within a microfluidic channel. [181] The innovative design of this platform featured a piezoelectric transducer used to focus and deform cells acoustically, alongside a laser-based interferometer to detect changes in the cells' optical patterns.…”