Microtubular Teardrop Patterning and the Growing Process
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Microtubular Teardrop Patterning and the Growing Process Kosuke Okeyoshi1, 2, Kawamura Ryuzo1, 3, and Yoshihito Osada1 1
RIKEN, Advanced Science Institute, 2-1 Hirosawa Wako-shi, Saitama 351-0198, Japan
2
Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
3
BioMedical Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki 305-8562, Japan
ABSTRACT Here we show that microtubular bundles bend flexibly under a hydrodynamic flow to form teardrop patterns. In a highly concentrated microtubular solution, patterns of same-sized teardrops form according to the maximum critical curvature, which is determined by the specific rigidity of the microtubules. Our understanding is that these micropatterns grow when microtubular bundles with hydrodynamic flow energy are converted into stable teardrop patterns as a higher structure. This conversion is generated by the combined effect of multiple kinds of energy, including heat and hydrodynamic flow, as well as life systems. These self-generating patterns in a spatio-temporal stream are reminiscent of what the artist Edward Munch called a scream of nature. We also envision that microtubular pattering with hierarchical structure will broaden the potential application of these geometrical structures and guide biomimetic material engineering towards areas such as integrated energy conversion, soft material patterning, and living signal transduction.
INTRODUCTION Microtubules, a type of cytoskeletal filament, are tubular molecular assemblies of α/βtubulin heterodimers that form rigid cylindrical filaments with diameters of 25 nm and lengths of tens of micrometers. Because of their geometrically determined structure and specific rigidity, the bending properties of microtubules have been widely studied.1, 2, 3 In vivo, microtubules play vital roles in assisting asymmetric cell division, mass transportation, and flagellar motion
processes that are observed up to micrometer scales depending on the cell size. In contrast, microtubules have huge potential for unique motions, and hierarchical structures4 over cell scales from tens to hundreds of micrometers in vitro. By integrating motor proteins or physical energy, the specific bending properties of microtubular bundles can be controlled for parallel-oriented bundles such as buckled wave-like structures and necklace-like structures.5, 6 These patterns are continuously oriented bundles such as stripes or wave patterns, showing the stability of parallel bundling. From the viewpoint of materials engineering, high-aspect rigid rod bundles in an integrated state at large scales should exhibit specific flexibility, structural stability, and cooperativity to form patterns. Actually, a flagellum succeeds in maintaining oscillation by using a sine-wave movement, and the periodic motion forms a spatial pattern of its own sine-waveshaped structure. This individual structure should lead to highe
