Fig. 2: Rolling adhesion measurements reveal catch-bond behaviour.
a, Schematic representation of a rolling adhesion experiment. Microparticles are bound to the surface of a microfluidic channel through catch bonds. A fluid flow through the channel imposes a shear rate \({\dot{\gamma }}\) across the particles, which makes them roll forward, continuously breaking and forming bonds. Stabilization of the interface, through catch-bond activation or an increase in bond density, causes particles to stop. b, Brightfield microscopy images showing a rolling and a stopped particle over time. c, Fraction of rolling particles froll as a function of \({\dot{\gamma }}\) for the catch-bond candidate and the slip-bond control. For catch bonds, froll decreases with increasing \({\dot{\gamma }}\). d, Displacement trace of a rolling particle, showing intermittent stop–roll behaviour, from which the stop time tstop and rolling velocity vroll are determined. e, A plot of the average vroll for particles bound with slip and catch bonds shows that catch-bonded particles are much less sensitive to changes in \({\dot{\gamma }}\). f, A plot of the average tstop over \({\dot{\gamma }}\) indicates that particles bound through catch bonds typically have larger stopping times. Shaded zones in e and f indicate standard deviations. The numbers of particle trajectories analysed per datapoint are listed in Supplementary Tables 3c and 4e,f.
