DOI: 10.5061/dryad.8931zcrzf
title: Catch bond kinetics are instrumental to cohesion of fire ant rafts under load

description: Dynamic networks composed of constituents that break and reform bonds
 reversibly are ubiquitous in nature owing to their modular architectures
 that enable functions like energy dissipation, self-healing, and even
 activity. While bond breaking depends only on the current configuration of
 attachment in these networks, reattachment depends also on the proximity
 of constituents. Therefore, dynamic networks composed of macroscale
 constituents (not benefited by the secondary interactions cohering
 analogous networks composed of molecular-scale constituents) must rely on
 primary bonds for cohesion and self-repair. Toward understanding how such
 macroscale networks might adaptively achieve this, we explore the uniaxial
 tensile response of 2D rafts composed of interlinked fire ants (S.
 invicta). Through experiments and discrete numerical modeling, we find
 that ant rafts adaptively stabilize their bonded ant-to-ant interactions
 in response to tensile strains, indicating catch bond dynamics.
 Consequently, low-strain rates that should theoretically induce creep
 mechanics of these rafts instead induce elastic-like response. Our results
 suggest that this forcestabilization delays dissolution of the rafts and
 improves toughness. Nevertheless, above 35% strain low cohesion and stress
 localization cause nucleation and growth of voids whose coalescence
 patterns result from force-stabilization. These voids mitigate structural
 repair until initial raft densities are restored and ants can reconnect
 across defects. However mechanical recovery of ant rafts during cyclic
 loading suggests that— even upon reinstatement of initial densities—ants
 exhibit slower repair kinetics if they were recently loaded at faster
 strain rates. These results exemplify fire ants’ status as active agents
 capable of memory-driven, stimuli-response for potential inspiration
 of adaptive structural materials.
description: # Catch bond kinetics are instrumental to cohesion of fire ant rafts under
 load
 [https://doi.org/10.5061/dryad.8931zcrzf](https://doi.org/10.5061/dryad.8931zcrzf) This respository contains the raw videos, data sets, and analysis codes used to generate the results of the manuscript titled above. ## Description of the data and file structure Raw video footage used for analysis in this work is provided in MP4 format for top-views of the fire ant rafts (used to conduct image analysis) and MOV format for the side views of the springs (whose elongation was measured to estimate ant raft restistance forces). File naming convention is as follows: * Top view footage of fire ant rafts loaded to uniaxial failure (at variable rates) and the corresponding side views of the springs used to estimate their resistance forces follow the filename formats *T**-Top-**.MP4* and *T**-Force-**.MOV*, respectively. Here, the sample number is an integer in the range [1,4] and the loading speed is a value in the set {20,60,120,240,360} (in units of [mm/min]). * Top view footage of fire ant rafts loaded cyclically (twice to 50% strain with variable hold times between cycles) and the corresponding side views of the springs used to estimate their resistance forces follow the filename formats *Cyclic-T**-Top-**-**.MP4* and *Cyclic-T**-Force-**-**.MOV*, respectively. Here, the sample number is an integer in the range [1,4], the loading speed is a value in the set {120,240} (in units of [mm/min]), and hold time is a vlue in the set {0,10,30,60,300} (in units of [s]). All experimental analysis methods and data are provided in compressed folders as follows. Each folder contains its own README.txt files with detailed explanations of its contents: * *Stress & Damage Analysis*, which contains raw data and source code (written in MATLAB) used to conduct damage analysis and plot outputs such as stress-strain, void characteristics with respect to strain, etc.; * *Measure ka and kd* which contains the raw image stacks (stored as .gif files) used to measure ant-to-ant attached and detached bond lifetimes using ImageJ, as well as the MATLAB script used to compute average attachment and detachment rates from this data; * and *Conformational PIV Analysis* which contains the PIVlab sessions and MATLAB source code used to conduct particle image velocimetry (PIV) on ant rafts and then compute outputs such as local rate of spin, expansion/contraction, etc. Contents related to the discrete numerical model with a detailed readme (*README.md*) can be found in the compressed folder *DiscreteNumModel*.