Rheology of Entangled Active Polymer-Like T. Tubifex Worms

Abstract

We experimentally study the rheology of long, slender, and entangled living worms (Tubifex Tubifex). Their level of activity can be controlled by changing the temperature or by adding small amounts of alcohol to make the worms temporarily inactive. Performing classical rheology experiments on this entangled polymer-like system, we find that the rheology is qualitatively similar to that of usual polymers, but, quantitatively, (i) shear thinning is reduced by activity, (ii) the characteristic shear rate for the onset of shear-thinning is given by the time scale of the activity, and (iii) the low shear viscosity as a function of concentration shows a very different scaling from that of regular polymers. Our study paves the way towards a new experimental research field of active "polymer-like worms."

Phase Separation by Entanglement of Active Polymerlike Worms

“…The T. tubifex worms that we investigate are active swimmers and approximately 300 μm thick and 10-40 mm long (see Supplemental Material [21]). The thermal random motion of the worms (estimated from the Stokes-Einstein equation) is negligible compared to their active motion, so they constitute a good model system for active polymers [25][26][27][28][29][30]. When randomly distributed over a volume of water, the worms aggregate spontaneously (Fig.…”

Computational exploration of treadmilling and protrusion growth observed in fire ant rafts

“…Condensed active matter is defined as an ensemble of constituents that consume energy to do mechanical work while remaining entangled or in physical contact with one another (Hu et al, 2016). Examples of such systems are omnipresent in nature and include systems ranging from the cytoskeletal walls of single cells (Neuhaus et al, 1983) to clustered aggregations of worms or insects (Adams et al, 2011; Deblais et al, 2020; Peleg et al, 2018). This material class is exemplary for its ability to display complex cooperative behavior and morph despite remaining cohesively unified.…”

Emergent collective locomotion in an active polymer model of entangled worm blobs

“…Motivated by these experiments and insights on aggregations of blackworms and sludge worms [17,23,16], we pursue a theoretical model that captures the collective behavior of aquatic worms by linking together local rules governing interactions between individual worms with the emergent macroscale dynamics of the blob.…”

“…Other recent work has investigated the rheology and phase separation in aggregations of a similar organism, Tubifex tubifex , also called the sludge worm or sewage worm. These worms also form highly entangled blobs in water to minimize exposure to poisonous dissolved oxygen, though collective locomotion has not been observed [23, 16]. It was shown that modeling the aggregation of small worm blobs into larger blobs as the coalescence of droplets undergoing Brownian motion was insufficient to capture the dynamics observed in the experiments [16].…”

“…Motivated by these experiments and insights on aggregations of blackworms and sludge worms [17, 23, 16], we pursue a theoretical model that captures the collective behavior of aquatic worms by linking together local rules governing interactions between individual worms with the emergent macroscale dynamics of the blob. Worms consume energy in order to propel themselves, and as such we look toward the extensive body of research in modeling active polymers and worm-like filaments, where activity can be implemented in different ways, such as via colored noise or a constant tangential force [24, 25, 26, 27, 28].…”