This grant will support the development of a magnetic tweezers apparatus to measure local viscoelastic and structural properties of the cell cytoplasm and the extracellular matrix. The magnetic tweezers produce a magnetic field of known magnitude and direction. The field exerts a magnetic force on spherical magnetic particles with definite geometric and magnetic properties, which are injected into the cytoplasm or matrix. The motion of the magnetic particle is monitored using optical methods. The trajectory of the particle is recorded on a computer. Simultaneously, the motion of the particle is also described in terms of standard models. The local viscoelastic parameters of the cytoplasm or matrix are obtained from the matching of the model trajectory and the experimentally obtained trajectory. The knowledge of these parameters provides information on the local structure of interconnected networks of biological macromolecules that exist in the cytoplasm (i.e. cytoskeleton) and the extracellular matrix. The magnetic tweezers will also be used to study intracellular stress propagation. At present the magnetic tweezers are the only apparatus that allows the measurement of local viscoelastic properties of biological systems in a non-destructive way. By combining several magnetic tweezers, effects similar to those produced by optical tweezers could be generated. The laser traps in the latter case are analogous to magnetic traps in the former case. At the same time, the costs associated with the development and operation of a magnetic tweezers are significantly lower.
