Interplay of Structure, Elasticity, and Dynamics in Actin-Based Nematic Materials

Journal Article · Tue Jan 09 00:00:00 EST 2018 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.1713832115· OSTI ID:1459902

Zhang, Rui ^[1]; Kumar, Nitin ^[2]; Ross, Jennifer L. ^[3]; Gardel, Margaret L. ^[4]; de Pablo, Juan J. ^[5]

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1. Univ. of Chicago, IL (United States). Inst. for Molecular Engineering
2. Univ. of Chicago, IL (United States). James Franck Inst.; Univ. of Chicago, IL (United States). Dept. of Physics
3. Univ. of Massachusetts, Amherst, MA (United States). Dept. of Physics
4. Univ. of Chicago, IL (United States). James Franck Inst.; Univ. of Chicago, IL (United States). Dept. of Physics; Univ. of Chicago, IL (United States). Inst. for Biophysical Dynamics
5. Univ. of Chicago, IL (United States). Inst. for Molecular Engineering; Argonne National Lab. (ANL), Argonne, IL (United States). Inst. for Molecular Engineering

Achieving control and tunability of lyotropic materials has been a long-standing goal of liquid crystal research. Here we show that the elasticity of a liquid crystal system consisting of a dense suspension of semiflexible biopolymers can be manipulated over a relatively wide range of elastic moduli. Specifically, thin films of actin filaments are assembled at an oil-water interface. At sufficiently high concentrations, one observes the formation of a nematic phase riddled with +/- 1/2 topological defects, characteristic of a two-dimensional nematic system. As the average filament length increases, the defect morphology transitions from a U shape into a V shape, indicating the relative increase of the material's bend over splay modulus. Furthermore, through the sparse addition of rigid microtubule filaments, one can gain additional control over the liquid crystal's elasticity. We show how the material's bend constant can be raised linearly as a function of microtubule filament density, and present a simple means to extract absolute values of the elastic moduli from purely optical observations. Finally, we demonstrate that it is possible to predict not only the static structure of the material, including its topological defects, but also the evolution of the system into dynamically arrested states. Despite the nonequilibrium nature of the system, our continuum model, which couples structure and hydrodynamics, is able to capture the annihilation and movement of defects over long time scales. Thus, we have experimentally realized a lyotropic liquid crystal system that can be truly engineered, with tunable mechanical properties, and a theoretical framework to capture its structure, mechanics, and dynamics.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: Army Research Office (ARO); National Science Foundation (NSF); USDOE
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1459902
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 2 Vol. 115; ISSN 0027-8424
• Publisher: National Academy of Sciences, Washington, DC (United States)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
actin
elasticity
lyotropic liquid crystal
microtubule
topological defects