Active Gel

We form an isotropic, percolating active network composed of microtubules, Kinesin motor proteins, and PEG. The constituent microtubule filaments form bundles which primarily extend along their length. At high density, these extending bundles become entangled with neighboring bundles and extensile forces lead to bending and subsequent buckling of the bundle. The broken bundles merge with nearby bundles and continue the process of extension, bending, buckling and merging.

Active Gel Microdynamics

Bundle extension, bending, buckling, and merging.

Constituent Components

The fundamental components in the active gel are microtubules, kinesin motors, and PEG. Together, these form extending bundles which build a percolating active gel.

More about the Components

Active Gel in Motion

Unlike a passive, equilibrium liquid or gel, this type of active gel exists far-from-equilibrium due to the Kinesin motor proteins exerting inter-filament sliding forces. This internal driving endows the active gel with properties that are not found in traditional materials. One such property are large, internally generated flows which are driven by microdynamics described above. In other words, this is a fluid which can actually mix itself.

The active gel observed with fluorescence microscopy. Bundles extending lead to the percolating network seen in this video. The FOV width is approximately 500 microns and is sped up ~10x.

Characterizing the Active Gel

Varying ATP tunes the characteristic speed of the active gel.

Adding tracer particles of the active gel allows easy visualization of the flow patterns in the system.

Kinesin motor walking speeds are dependent on the concentration of ATP in the solution. We can therefore tune the speed at which the system moves by changing the concentration of ATP in the solution. On the left is a series of experiments from a low concentration to a high concentration of ATP shown in fluorescence.

​We quantify the flow internally generated by adding tracer particles to the fluid. We can then measure flow velocity, two-point spatial velocity correlations, and tracer particle mean squared displacements (MSDs).

Mean Squared Displacements (MSDs) of tracer particles suspended in the active gel.

We also measure a characteristic speed of the active gel as a function of ATP concentration from the MSD data above. This data shows that below a saturating level, the speed of the system is tunable.

For more information about the characterization we have completed on the active microtubule gels, please check out the following publications.
​
Tunable dynamics of microtubule-based active isotropic gels
G. Henkin*, S. J. DeCamp*, DT. Chen*, T. Sanchez, Z. Dogic
​Phil. Trans. R. Soc. A. Nov 2014; 372(2029).

Spontaneous Motion in Hierarchically Assembled Active Matter
T. Sanchez*, DT. Chen*, S. J. DeCamp*, M. Heymann, Z. Dogic
Nature, Nov 2012; 491(424): 431-4.
​(News and Views by: M. Christina Marchetti)