Shell mechanics of suspended mammalian cells

Most animal cells are mechanically stabilized by an actin cortex. The actin cortex is believed to not only maintain cell structural integrity, but to also sense mechanical cues from the environment, which affect cell migration, focal adhesion formation, and cell differentiation. The mechanical properties of the actin cortex itself are believed to adapt in response to external cues. Here, we utilize optical tweezers in microfluidic flow chambers to conduct single-cell microrheology to measure the mechanical response of suspended mammalian cells. We compare changes in cortical mechanics of three types of cells when exposed to drug treatments and to non-physiological osmolarity. We constructed a FEM model in Abaqus and find that the experiment results can be well explained by modeling a cell as a thin elastic shell surrounding a highly viscous cytoplasm. We find cortical stiffnesses in the range of several kPa.