Abstract
We present a high-throughput microfluidics technique facilitating in situ measurements of cell mechanics parameters at the dorsal side of the cell, including molecular binding strengths, local traction forces, and viscoelastic properties. By adjusting the flow rate, the force magnitude exerted on the cell can be modulated ranging from ~14 pN to 2 nN to perturb various force-dependent processees in cells. Time-lapse images were acquired to record events due to such perturbation. The values of various mechanical parameters are subsequently obtained by single particle tracking. Up to 50 events can be measured simultaneously in a single experiment. Integrating the microfluidic techniques with the analytic framework established in computational fluid dynamics, our method is physiologically relevant, reliable, economic and efficient.
Highlights
Dorsal traction forces are of biological importance as well
Www.nature.com/scientificreports transmitted to the key immunosuppressing molecule cytotoxic T-lymphocyte-associated protein 4 (CTLA4)[30,31,32,33,34] on the surface of cancer cells. It has been reported CTLA4 was involved in mechanically engaging its ligands CD80 or CD86 leading to immunosuppression[28,30,35,36], though the magnitude of the mechanical forces transmitted via CTLA4 is yet to be quantified
We tracked the displacement of micron-sized particles conjugated with CD80, which bound to CTLA437 on the surface of breast cancer cells (MDA-MB-231)
Summary
We first set out to demonstrate that we could measure traction forces at the dorsal side of the cell. Based on the tracking results, we calculated the magnitude of the traction force generated by the cells to overcome the hydrodynamic forces and subsequently move the particle in the direction opposite to the flow. The results obtained from the magnetic tweezers showed traction force values exerted through CTLA4-CD80 were of the same order of magnitudes with the results using our microfluidics-based method with no significant difference between the two measurement methods (Supplementary Fig. S6). The number of cell-bound particles did not further decrease even when higher forces were applied, indicating a sub-population of bonds between integrin and anti-integrin antibody exist, where the required rupture force is much higher than the maximal hydrodynamic forces in our platform. By evaluating the contact area between the particle and the cell surface (Fig. 2c), the dorsal traction force generated per unit area can be estimated. Our technique thereby is relevant in physiological scenarios and can be applied, for example, to evaluate forces required to disrupt cancer cell-endothelium association via ICAM-MUC157 bond before intrastation is initiated, or to evaluate the pulling force, transmitted through Notch and its ligands at the cell-cell interface during embryonic development[58]
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