(721f) 3-Dimensional Mechanics and Shapes of Cells On Micropatterned Substrates

Mechanical properties and shapes of cells have been studied intensely in bacteria, anuclear erythrocytes, lymphocytes and various adherent eukaryotic cells in conjunction with cytoskeletal structure and dynamics. In these experiments, cell mechanics have been probed using methods such as atomic force microscopy, optical tweezers, microrheology, magnetic twisting cytometry, micropipette aspiration, and elastic micropatterned/structured substrates. Concurrently, various theoretical models have been proposed that describe cells as liquid-like droplets, vesicles, gels, glassy material, elastic material, viscoelastic material, or tensegrity structures held by the balance between contractile actin filaments and compression-resistant microtubules. These models can reproduce some aspects of cellular mechanics, but none offers a unifying description that would reproduce mechanical properties and shapes of cells of different types in quantitative detail.

Our studies rule out description of the cell shape by simple droplet or vesicle models. Instead, the observed shapes are well described by the minima of an energy functional comprising terms due to the cell membrane and cortical actin deformations and with a boundary condition reflecting the limited incompressibility of the nucleus. Our model predicts that the load-bearing portions of the cytoskeleton (notably, the microtubules) have no effect on the cell shape. This prediction is at odds with the tensegrity model but is confirmed by experiments in which the microtubules are selectively dissolved depolymerized without affecting cell topography. The current work provides a set of experimental and theoretical tools with which to study and quantify cell mechanics and shapes non-invasively and under well defined conditions.