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Systematic Analysis of In Vitro Cell Rolling Using a Multi-well Plate Microfluidic System
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Microrollers flow uphill as granular media.
Samuel R Wilson-Whitford1, Jinghui Gao1, Maria Chiara Roffin1,2
1Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA, 18015, USA.
Nature Communications
|September 20, 2023
Summary
Researchers created a system where microrollers roll uphill against gravity, forming a heap with a negative angle of repose. This granular material behavior challenges traditional physics, mimicking dissipative systems.
Area of Science:
- Physics
- Materials Science
- Engineering
Background:
- Granular materials typically exhibit a positive angle of repose due to friction.
- Collective motion in granular flows is usually limited to the surface layer and dissipates energy.
Purpose of the Study:
- To investigate the collective behavior of granular materials when torque is applied at the individual particle level.
- To demonstrate a system exhibiting a negative angle of repose.
Main Methods:
- Applying torque to individual microrollers using a rotating magnetic field in a dense particle bed.
- Utilizing velocimetry to analyze the motion of particles in the near-surface flowing layer.
Main Results:
- Microrollers were observed to roll uphill, forming a heap with a negative angle of repose.
- Two distinct flow regimes were identified based on particle mobility and fluidization.
- Particle motion in the flowing layer scaled similarly to traditional granular flows.
Conclusions:
- The experimental system successfully generated macroscopic collective behavior with the kinematics of a dissipative granular system.
- A simple granular model incorporating cohesion accurately predicted the observed negative coefficient of friction.
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