Abstract
Suspensions of microtubules and nonadsorbing particles form thick and long bundles due to depletion forces. Such interactions act at the nanometer scale and define the structural and dynamical properties of the resulting networks. In this study, we analyze the depletion forces exerted by two types of nonadsorbing particles, namely, the polymer, poly(ethylene glycol) (PEG), and the block copolymer, Pluronic. We characterize their effects both in passive and active networks by adding motor proteins to the suspensions. By exploiting its bundling effect via entropic forces, we observed that PEG generates a network with thick structures showing a nematic order and larger mesh size. On the other hand, Pluronic builds up a much denser gel-like network without a recognizable mesh structure. This difference is also reflected in the network activity. PEG networks show moderate contraction in lateral directions while Pluronic networks exhibit faster and isotropic contraction. Interestingly, by mixing the two nonadsorbing polymers in different ratios, we observed that the system showed a behavior that exhibited properties of both agents, leading to a robust and fast responsive structure compared to the single-depletant networks. In conclusion, we show how passive osmotic compression modifies the distribution of biopolymers. Its combination with active motors results in a new active material with potential for nanotechnological applications.
Highlights
The collective behavior of molecules transducing energy into motion underlies many biological processes and enables vital functions that lead to what we call “life”
We show how depletion interactions caused by polymers of different natures in solution and activity of motor proteins differently affect the properties and dynamic behavior of biopolymer networks
Microtubule mixture was prepared by 2.7 mg/mL 488 HiLyte-labeled porcine brain tubulin (Cytoskeleton, Inc.) in M2B with 5 mM MgCl2, 1 mM GTP, 5% dimethyl sulfoxide (DMSO), 0.5 mg/mL glucose, We conducted experiments by mixing taxol-stabilized microtubules with the two different depletants, poly(ethylene glycol) (PEG) and Pluronic, and we studied their effects on the network behavior in three different cases: (i) a nonactive network made of a depletant (PEG or Pluronic) and biopolymers, (ii) a network, made of a
Summary
The collective behavior of molecules transducing energy into motion underlies many biological processes and enables vital functions that lead to what we call “life”. Dynamics, and functionalities that these intracellular microscopic elements can generate has tremendously grown in the last decades. Their potential for the development of new bioinspired nanomaterials is currently providing the impetus for new research directions.[1] Bottom-up assembled biomolecular structures have started to emerge as model systems that can reproduce the behavior of a living ensemble and elucidate fundamental mechanisms underlying emergent behavior in nature. Convenient biological components for such active materials are the biopolymers and motor proteins from the cellular cytoskeleton In the cell, these components form self-organizing networks with different architectures according to the needs for spatial and functional organization. Foundational studies showed that simplified in vitro systems greatly improved our understanding of the complex selforganizing organisms they originate from.[2−6]
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