(in collaboration with Leah Keshet)

The motion of a eukaryotic cell raises a variety of interesting and challenging questions, both physical-mechanical and biological. In a highly simplified picture, the cell responds to a chemical attractant by initiating a complex array of biochemical reactions inside, which leads to its polarization, i.e., the formation of a front and a back (see PhD thesis of A. Jilkine for background). At the front, high level of certain signaling proteins triggers polymerization of actin filaments that in turn produces a protrusion force on the elastic membrane of the cell. Consequently the cell deforms and moves. As an example, The image below links to well-known movie footage of a neutrophil chasing down bacteria.

We have built a chemico-mechanical model (full text) for this process by integrating the biochemistry responsible for polarization and the solid-fluid mechanics underlying the deformation and movement. The animation below illustrates a simulation of a cell that polarizes and then moves after a transient chemical stimulation. The color indicates levels of the signaling molecule. Details can be found in Vanderlei et al. (full text).

In a more recent project, we used a particle-based method to study the loss of deformability of malaria-infected red blood cells (RBCs). To match the deformation of RBCs stretched using optical tweezers, we found that the mechanical effect of the parasite has to be explicitly accounted for. Through the ring, trophozoite and schizont stages of infection, the gradual rigidification of the RBC is largely a result of the growth and eventual division of the merozoites inside. Details can be found in Hosseini and Feng (2010) (full text).