  Mechanical stresses are increasingly found to be associated with various
biological functionalities. At the same time, topological defects are being
identified across a diverse range of biological systems and are points of
localized mechanical stress. It is therefore important to ask how mechanical
stress localization around topological defects is controlled. Here, we use
continuum simulations of nonequilibrium, fluctuating and active nematics to
explore the patterns of stress localization, as well as their extent and
intensity around topological defects. We find that by increasing the
orientational elasticity of the material, the isotropic stress pattern around
topological defects is changed substantially from a stress dipole characterized
by symmetric compression-tension regions around the core of the defect to a
localized stress monopole at the defect position. Moreover, we show that
elastic anisotropy alters the extent and intensity of the stresses, and can
result in the dominance of tension or compression around defects. Finally,
including both nonequilibrium fluctuations and active stress generation, we
find that the elastic constant tunes the relative effect of each, leading to
the flipping of tension and compression regions around topological defects.
This flipping of the tension-compression regions only by changing the elastic
constant presents an interesting, simple, way of switching the dynamic behavior
in active matter by changing a passive material property. We expect these
findings to motivate further exploration tuning stresses in active biological
materials by varying material properties of the constituent units.
