Mechanical anisotropy of viscoelasticity in biological cells

The mechanism that biological cells use to remodel their cytoskeletal structure in response to external stress is unclear. Experimental observations suggest that the cells remodel their skeleton in a manner that is directionally responsive to the external stress. In order to understand these directional responses, we developed a method to measure the rheological response of the cell in orthogonal directions simultaneously. To achieve controlled stimulation and detection, we used a dual-beam optical tweezer, which used a pump and probe scheme to measure the storage and loss modulus of the cellular cytoskeleton. The pump was used to manipulate extracelluar micro-particles which were attached to the actin cytoskeleton through trans-membrane integrin alpha receptors. By measuring two independent regions of the cell, we were able to generate a localized mechanical stress on the outer surface of the cell while observing the directionally specific inside response.