Emulsion biomechanics for single cells [electronic resource]
Keywords: Electrical Engineering.

Personalized medicine will increasingly depend on understanding and identifying cellular and molecular heterogeneity at the single cell level. Development of both macro and microscale approaches for probing single cells takes on increasing importance in understanding this heterogeneity. Label-free approaches may be broadly classified as those analyzing biophysical properties (bioelectrical and biomechanical) and those analyzing biochemical properties. Significant technical challenges, however, include cost and throughput. Microfluidic approaches for probing single cells are growing due to the many advantages that microfluidics may afford including cost, throughput, sensitivity, and footprint. This dissertation describes the development of a new, noncontact approach for probing single cell mechanics termed Emulsion Biomechanics for Single Cells. Droplets present a uniquely controllable, chemomechanical microenvironment in which to study cell mechanics. The microenvironment is contained within a well defined droplet volume that can be engineered and tuned with prescribed chemical and physical properties. In this technique single cells are first captured inside droplets. A unique flow field exists inside the droplet due to coupling of the external and internal flow field of the droplet. The cell mechanically responds to this internal flow field by undergoing multiple orbits, spins, and deformations that depend on its physical properties. This behavior is captured through high-speed imaging and provides additional insight in to the cell's mechanical properties. Emulsion Biomechanics may also present a new label-free modality for detection and sorting of rare cells based on mechanical properties. Two different high throughput Emulsion Biomechanics methods were developed: Direct Deformation and Accelerating Flow. In Direct Deformation the droplet is perturbed in to an unfavorable energy state deviating far from spherical. Upon relaxation an extensional flow field results inside the droplet. A single cell being subjected to this flow field mechanically responds through measureable deformation. In Accelerating Flow, the external flow field couples to the internal flow field through viscous traction at the interface resulting in a rotational flow field inside the droplet. A single cell being subjected to this flow field experiences orbital translation and mechanically responds with a unique combination of trajectory, speed, and spin. Through a combination of numerical modeling and experimental validation, the following Emulsion Biomechanics estimates were made using Accelerating Flow with Fluorinert FC-40 as the oil phase and MDA-MB-231 breast cancer cells in the suspension phase. Droplet generation rates of 100 per sec were typical. Experimentally a single orbital period requires approximately 100 ms with angular rotation rate of 18.8 rev/s at an oil flow rate Qoil of 3.5 µL/min. Estimated flow velocity difference was 3 mm/s. Small cell deformation of 0.05 also resulted. Numerical estimate of settling time in the vortex is 250 ms for a 10 µm diameter cell. Numerical estimate of sensitivity of angular rotation rate to size is 0.7 rev/s/µm when settled in to the vortex.