Probing active nematics with in-situ microfabricated elastic inclusions

TL;DR

This paper introduces a novel in-situ microfabrication method to measure forces, rheology, and defect mechanics in active nematic gels, providing new insights into their physical properties and behaviors.

Contribution

Develops a rapid photo-polymerization technique for elastic inclusions in active nematics, enabling direct force measurement and validation of theoretical models.

Findings

Measured forces exerted by active nematic gels.

Quantified shear viscosity and activity parameter.

Validated theoretical relationships between rheological properties.

Abstract

In this work, we report a direct measurement of the forces exerted by a tubulin/kinesin active nematic gel as well as its complete rheological characterization, including the quantification of its shear viscosity, {\eta}, and its activity parameter, {\alpha}. For this, we develop a novel method that allows us to rapidly photo-polymerize compliant elastic inclusions in the continuously remodelling active system. Moreover, we quantitatively settle long-standing theoretical predictions, such as a postulated relationship encoding the intrinsic time scale of the active nematic in terms of {\eta} and {\alpha}. In parallel, we infer a value for the nematic elasticity constant, K, by combining our measurements with the theorized scaling of the active length scale. On top of the microrheology capatilities, we demonstrate novel strategies for defect encapsulation, quantification of defect mechanics, and defect interactions, enabled by the versatility of the new microfabrication strategy that allows to combine elastic motifs of different shape and stiffness that are fabricated in-situ and on-time.