Size- and speed-dependent mechanical behavior in living mammalian cytoplasm
Author(s)
Jafari, Somaye; Cai, Shengqiang; Hu, Jiliang; han, yulong; Grodzinsky, Alan J; Guo, Ming; ... Show more Show less
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Active transport in the cytoplasm plays critical roles in living cell physiology. However, the mechanical resistance that intracellular compartments experience, which is governed by the cytoplasmic material property, remains elusive, especially its dependence on size and speed. Here we use optical tweezers to drag a bead in the cytoplasm and directly probe the mechanical resistance with varying size a and speed V. We introduce a method, combining the direct measurement and a simple scaling analysis, to reveal different origins of the size- and speed-dependent resistance in living mammalian cytoplasm. We show that the cytoplasm exhibits size-independent viscoelasticity as long as the effective strain rate V/a is maintained in a relatively low range (0.1 s −1 < V/a < 2 s −1 ) and exhibits size-dependent poroelasticity at a high effective strain rate regime (5 s −1 < V/a < 80 s −1 ). Moreover, the cytoplasmic modulus is found to be positively correlated with only V/a in the viscoelastic regime but also increases with the bead size at a constant V/a in the poroelastic regime. Based on our measurements, we obtain a full-scale state diagram of the living mammalian cytoplasm, which shows that the cytoplasm changes from a viscous fluid to an elastic solid, as well as from compressible material to incompressible material, with increases in the values of two dimensionless parameters, respectively. This state diagram is useful to understand the underlying mechanical nature of the cytoplasm in a variety of cellular processes over a broad range of speed and size scales. Keywords: cell mechanics; poroelasticity; viscoelasticity; cytoplasmic state diagram
Date issued
2017-08Department
Massachusetts Institute of Technology. Department of Biological Engineering; Massachusetts Institute of Technology. Department of Mechanical EngineeringJournal
Proceedings of the National Academy of Sciences
Publisher
National Academy of Sciences (U.S.)
Citation
Hu, Jiliang et al. “Size- and Speed-Dependent Mechanical Behavior in Living Mammalian Cytoplasm.” Proceedings of the National Academy of Sciences 114, 36 (August 2017): 9529–9534 © 2017 National Academy of Sciences
Version: Final published version
ISSN
0027-8424
1091-6490