Jen Joyce, University of North Carolina at Chapel Hill


Biomechanics of a Blebbing Cell

Abstract:  Cells are enclosed in plasma membranes, and these membranes are elastic bodies that can deform due to forces and pressures imposed by many biological factors.  A “bleb” is a bud or balloon-like protrusion in the plasma membrane.  Blebs aid in cell motility and also play a key role in the break-up of a cell during apoptosis (cell death).  How exactly the bleb forms, is unknown. 
To investigate the phenomenon of bleb formation, we are developing a model for this fluid/structure interaction.  The inside of the cell is composed primarily of water.  There are thousands of actin filaments inside the cell tethered to the plasma membrane that help maintain the cell’s structure and shape.  The length and attachment strength of these filaments is determined by proteins and chemicals in the cell such as calcium and myosin. 
Currently, we have set up a model to mimic the filament-membrane-fluid interaction in a cell.  Using a finite-element program called FreeFEM, in conjunction with C++ code, the code begins with initial data such as internal pressure in the cell, fluid velocity within the cell, filament length, etc, and then simply evolves according to this initial information.  We use Stokes’ equations to solve the fluid problem, Lame’s equations to solve the elastic membrane problem, and spring-force equations to model the filaments.  These three structures interact through boundary-value forces and velocities on the interior of the cell membrane. 
We are working on testing the following theory:  If we were to break enough filament-membrane connections in one specific section of the cell, would that cause a bleb to form in that area?  There would be less filaments holding the membrane, so with enough internal pressure, one would expect the membrane to balloon out in this un-tethered spot.


Advisor: Sorin Mitra (UNC)