Sketch of a typical cell with mechanically important components.

Finite element analysis of the aspiration of a droplet consisting of actin network enveloping a very soft core.

The cytoskeleton is the main promoter of cell stiffness and plays a crucial role in maintaining cell shape. It is involved in cell migration, cell division and active contraction. Interactions are not limited to mechanical transmission of forces but also biochemical processes are triggered. Such interactions may be summarized with the term mechanotransduction, which includes cell force transmission from the extracellular matrix to the cytoskeleton. Experiments show that the orientation of the cytoskeleton is a function of the interplay between biochemical activity and the magnitude of stretching. Cell mechanics and thus the mechanics of the cytoskeleton are also important in a great number of diseases, e.g., malaria, asthma, arthritis, atherosclerosis, glaucoma and cancer, where the considered cells show different stiffness compared to their healthy counterparts. Knowledge of the mechanics may help to understand and improve diagnosis.

Actin is one of the key constituents of the cytoskeleton and has been the subject of extensive research over the last two decades. It is a globular protein that assembles into filaments. These filaments are linked together by actin binding proteins to form bundles and networks. The hierarchy implied by these assemblies leads to efforts to find mechanical material models for actin networks that describe their properties on more than one scale.

Our research focusses on continuum mechanical models that derive the constitutive equation based on the properties of the filaments and the microstructure. We strive to capture important biophysical features, e.g., viscoelasticity or the normal stress behavior under shear, which is remarkably different from that of ‘soft’ engineering materials such as rubber. Actin networks with relatively low network density are known to involve non-affine deformations and the actin binding proteins exhibit finite stiffness. Both phenomena are subject to our investigations.

Funding: Graz University of Technology