UC San Diego

The specific way in which individual cells coordinate their migratory behaviors during various physiological processes including morphogenesis, cancer progression or epithelial self-healing, largely depends on the mechanical properties and topology of the surrounding external environment. Collective cell migration has been traditionally studied in flat substrates ignoring tissue heterogeneity that is found in physiological conditions. In addition to this, existing literature has been mostly focused on contractile forces at the cell-ECM inter- face while leaving cell-cell force measurement under-looked as well as neglecting compressive or pushing forces. This dissertation addresses some of these limitations proposing a novel methodology to characterize collective cell migration when physical obstacles are present and provides a framework to quantitatively study the complex dynamics observed in developing tissues.

Force exertion is an integral part of cellular phenotype regulating important cell functions and fate. In order to quantify mechanical forces at the cellular scale, traction force microscopy has traditionally been considered a standard when quantification of forces at the cell-substrate interface are required. However, quantification of compressive and shear stresses in three dimensions have been elusive due to the lack of experimental and computational techniques appropriate for this sizable challenge. This dissertation presents a novel methodology to produce photo-initiated elastic round microgels that can be functionalized and embedded in three dimensional tissues for force quantification.

We also present a novel family of PDMS microfluidic devices with ∼1-micron narrow constrictions intended to characterize and quantify mechanical forces experimented by cells when they squeeze through narrow gaps in extracellular matrices, as observed in neutrophil migration or even cellular structures, as red blood cells squeezing through interendothelial slits in the spleen. At the cusp of each constriction, we harnessed capillary phenomena to embed photopolymerizable hydrogels of tunable geometry and mechanical properties, seeded with fluorescent ∼0.1-micron particles. As cells squeeze through the constrictions, the hydrogel deforms leading to motion of the fluorescent particles. This motion can be recorded with a microscope and analyzed to calculate stresses using traction force microscopy.