Imaging the microscopic viscoelastic anisotropy in living cells

Maintaining and modulating the mechanical anisotropy is essential for biological processes. How this is achieved on the microscopic scale in living soft matter is however not always clear. Here we introduce Brillouin Light Scattering Anisotropy Microscopy (BLAM) for mapping the high-frequency viscoelastic anisotropy inside living cells. Following proof-of-principle experiments on muscle myofibers, we apply this to study two fundamental biological processes. In plant cell walls we show how a phase-transition driven switch between anisotropic-isotropic wall properties may lead to asymmetric growth. In mammalian cell nuclei we uncover a spatio-temporally oscillating elastic anisotropy correlated to chromatin condensation, with long range orientational correlations that may provide a dynamic framework for coordinating intra-nuclear processes. Our results highlight the direct and indirect role the high-frequency mechanics can play in providing dynamic structure that lead to the regulation of diverse fundamental processes in biological systems, and offer a means for studying these. BLAM should find diverse biomedical and material characterization applications.