  The mechanics of animal cells is strongly determined by stress fibers, which
are contractile filament bundles that form dynamically in response to
extracellular cues. Stress fibers allow the cell to adapt its mechanics to
environmental conditions and to protect it from structural damage. While the
physical description of single stress fibers is well-developed, much less is
known about their spatial distribution on the level of whole cells. Here, we
combine a finite element method for one-dimensional fibers embedded in an
elastic bulk medium with dynamical rules for stress fiber formation based on
genetic algorithms. We postulate that their main goal is to achieve minimal
mechanical stress in the bulk material with as few fibers as possible. The
fiber positions and configurations resulting from this optimization task alone
are in good agreement with those found in experiments where cells in
3D-scaffolds were mechanically strained at one attachment point. For optimized
configurations, we find that stress fibers typically run through the cell in a
diagonal fashion, similar to reinforcement strategies used for composite
material.
