“…In general, the diffusivity of a solute through a crosslinked hydrogel decreases as crosslinking density increases, as the size of the solute increases and as the volume fraction of water within the gel decreases [ 18 ]. Because of wide application, in the last years, several methods have been developed to study bulk hydrogel properties, both theoretically and experimentally [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ].…”