The cells on the banner on the left are NIH 3T3 Fibroblasts, filled with fluorescently labelled 100 nm polystyrene spheres and imaged with fluorescence microscopy. In order to begin to understand these processes physically, we want to understand the cell's local mechanical properties. We use the thermal motion of small polystyrene beads to measure the local viscoelastic properties. We use a technique called Multiple Particle Tracking Microrheology . We have measured a variety of different types of behaviors with our multiple particle tracking technique.
Some particles appear to be moving randomly for at least part of their trajectory.
We can look for spatial co-localization of similar viscosities as shown below. The most mobile particles experience a low viscosity, as the visocity increases, the particles move less and less. Other particles appear to be caged - they are unable to move out of a local constraining volume. This may be due to the elastic nature of the medium, or due to local structure which physically prevents the particles from slipping past. Still other particles appear to be actively transported through the cell.