(648b) High-Throughput Surface Energy Characterization of Cell Suspension Using 3D Multiphase Centrifugal Microfluidics

The surface physiochemical properties of the cell membrane play a pivotal role in determining cell developmental fate, as well as mediating cell signaling, interaction, and migration in surrounding microenvironments. Common methods to characterize cell surface properties, such as surface energy, include population-based techniques (contact angle measurement of a layer of cells deposited on a substrate) and single cell techniques (atomic force microscopy with functionalized tips). Contact angle measurement is easy to conduct but is not directly applicable to cells in suspensions and lack of single-cell level characterization. AFM can provide precise mapping of the local surface energy on a sub-cellular level; however, AFM measurement can be cumbersome, and cells need to be immobilized on a substrate. Since biological cells are highly heterogeneous, a high-throughput method is required to directly characterize surface energy of cells in suspension with single-cell precision.

To address this need, we present a multiphase centrifugal microfluidic method which enables the measurement of single cell surface energy by directly imaging the phase translocation of cells under precisely controlled centrifugation. We design a 3D-printed microfluidic device with a circular microchannel that allows the introduction of two biocompatible and immiscible aqueous solutions, one containing Polyethylene Glycol (PEG) and the other Dextran (Dex), arranged in an concentric laminar flow pattern. We flow cells of interest into the inner phase and close the device with 3D-printed Luer-lock style channel caps. The device is placed in a customized centrifuge to enable centrifugal force-driven translocation of cells across the phase boundary between PEG and Dex while the concentric laminar flow profile is maintained by the closed channel set-up. The customized centrifuge provides programmed centrifugation steps and is integrated with a high-speed camera to capture the trapping and detachment of cells at the two-phase interface under controlled centrifugation. By imaging the phase translocation trajectory of cell suspensions, a scaling theory is developed to extract the surface energy of single cells based on force balance between centrifugal force, Stokes drag, and surface force due to interfacial energy gradient. The theory is further optimized empirically for different cell geometries, such as spherical shape and ellipsoidal shape. Our method is easy to implement, directly applicable to cells in suspension, and measures cell surface energy with single-cell precision. We validate the method with standard polystyrene microparticles and demonstrate its application by analyzing the surface physiochemical difference of chondrocytes extracted from healthy individuals and osteoarthritis patients and myoblasts differentiated in various stress conditions.