Comb Architecture to Control the Selective Diffusivity of a Double Network Hydrogel

Limiting the diffusion of small-sized substances (Dh < 5 nm) through hydrogels is particularly difficult to achieve. Herein, we demonstrate the utility of a comb architecture to systematically reduce the mesh size of a double network (DN) hydrogel to between ∼1 and 3 nm, without loss of hydration. Combs of varying charge, length, and concentration were introduced during the formation of the first network of the DN hydrogel based on thermoresponsive N-isopropylacrylamide and negatively charged 2-acrylamido-2-methylpropane sulfonic acid. The resulting hydrogels’ mesh sizes were characterized with a size-exclusion test. Negatively charged combs were the most effective in reducing mesh size, attributed to electrostatic repulsive forces with the DN. Due to a lack of interaction and attractive forces to the first network, respectively, neutral and particularly positively charged combs were less effective.