Tailoring Swelling Ratio of Smart Hydrogels by Utilizing Entropy-Driven Topologically Correlated Structures

Smart hydrogels, which can respond to external stimuli like temperature, pH, ionic strength, have shown great potential in tissue engineering, targeted drug delivery, regenerative medicine, and biochemical sensors etc. However, it is still challenging to use smart hydrogels with desired swelling properties in different application scenarios. Here a gel composite is designed which consists of polyanion guest chains and the positively charged host gel, and a method is introduced to quantitatively control the swelling ratio by tuning the topologically correlated structures and conformational entropy of guest chains with different molecular weight in the host gels. When the gels reach swelling equilibrium in water, the stable state of swelling, shrinking, and isovolumetric non-swelling can be precisely tuned simply by tuning the guest chain size. Neutron scattering measurements demonstrate that the gels have affine swelling behavior, where the swelling ratio of the macroscopic dimensions is consistent with that of the microscopic structures. It is suggested that this method represents a major advance to precisely control the swelling ratio as well as maintain the volume stability of smart hydrogels in an aqueous environment for their applications in tissue engineering and biochemical sensors.