Villus-like nanocomposite hydrogels with a super-high water absorption capacity

Network structure is one of the two most essential factors for determining the water absorption capability of super water absorbing hydrogels (SAHs). In this work, inspired by the function of small-intestinal villi which can increase the inner surface area of the small intestine by up to 600 times, a SAH with a villus-like structure is reported for the first time by the copolymerization of acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid using nanoparticles as the cross-linker. Such a unique villus structure can remarkably increase the surface area of SAHs in comparison with a porous or mesh-like structure of SAHs, leading to a significantly improved water absorbency of this villus-like SAH. The swelling ratios of this villus-like SAH are tremendously high up to 13 600 g g−1 in deionized water, 310 g g−1 in 0.9 wt% NaCl solution and 5200 g g−1 in 10 wt% urea solution, which are much higher than that of any previously reported water absorbing materials. This work opens a new route to create villus structures for SAHs with ultrahigh water-absorption capability, which may have promising applications in various fields such as agriculture, horticulture, hygienic products and daily chemicals.