  Control of the swelling, chemical functionalization, and adhesivity of
hydrogels are finding new applications in a wide range of material systems. We
investigate experimentally the effect of adsorbed particles on hydrogels on the
depinning of contact lines. In our experiments, a water drop containing
polystyrene microspheres is deposited on a swelling hydrogel, which leads to
the drop absorption and particle deposition. Two regimes are observed: a
decreasing drop height with a pinned contact line followed by a receding
contact line. We show that increasing the particles concentration increases the
duration of the first regime and significantly decreases the total absorption
time. The adsorbed particles increase the pinning force at the contact line.
Finally, we develop a method to measure the receding contact angle with the
consideration of the hydrogel swelling.
