Compositional Tuning Reveals a Pathway to Achieve a Strong and Lubricious Double Network in Agarose-Polyacrylamide Hydrogels

Hydrogels, bearing microstructural semblance to biological tissues, are prime candidates for translation replacement materials. Among them, double network (DN) hydrogels are at the forefront with their superior mechanical properties compared to conventional single network hydrogels. However, the functional design of the microstructure to control mechanical and tribological performance still poses a challenge. Here, hydrogels composed of physically crosslinked agarose and chemically crosslinked poly(acrylamide) were studied by spectroscopy, dynamic light scattering, atomic force microscopy and rheology. A viable hydrogel formed with the lowest acrylamide concentration, but the loose PAAm network did not reinforce the agarose network. Increasing the monomer and crosslinker concentration led to fast gelation of the second network, yielding poorly interconnected acrylamide-rich domains within the agarose network, and a weak and heterogenous hydrogel. Reducing the crosslinking degree to the half slowed down gelation, which favored the formation of an interpenetrating PAAm network, affording a two-fold increase in strength. While the adhesion of the investigated hydrogels is remarkably dictated and reduced by agarose, their frictional characteristics are highly sensitive to the composition. Importantly, friction can be modulated by varying the imbibed fluid.