Science 367, 1120–1124 (2020)

Nematic liquid crystals consisting of elongated units have long-range orientational order and topological defects. If the units can move, the nematic becomes ‘active’ with swirling flows and creation and annihilation of the defects. Active nematic systems arise in biological settings such as bacterial colonies and epithelial tissue but they have so far only been studied in two-dimensional (2D) systems. Guillaume Duclos and colleagues have now developed a 3D bulk active nematic and reconstructed its director field for the investigation of the structure of topological defects.

The team combined passive liquid crystals with a mixture of microtubules and molecular motors to create a 3D active nematic. They exploited the birefringence of the liquid crystal to track the director field using light-sheet microscopy and found that topological defects manifest as loops. The study offers a useful setup for developing and testing theoretical models of 3D active nematics and investigating the 3D counterpart of well-known 2D phenomena such as active turbulence.