A composite hydrogel exhibiting stiff response at low-strain regime by repulsion effect of positive/negative Poisson’s ratio

The application of hydrogels as substitutes for load-bearing tissues has garnered considerable attention. In contrast to load-bearing tissues, which can withstand complex loads with limited deformations, conventional hydrogels cannot exhibit a stiff response in the low-strain regime due to their soft natures. Herein, we reported the design of composite hydrogels inspired by the synergy between soft and hard constituents from load-bearing tissues. This design with a soft matrix (positive Poisson’s ratio) and hard skeletons (negative Poisson’s ratio) was up to 18.9 and 4.2 times stiffer than the matrix and skeleton, respectively. Instead, the combination of a soft matrix and skeletons with a positive Poisson’s ratio showed limited improvement. The underlying mechanism by the repulsion effect of positive and negative Poisson’s ratio between the soft matrix and hard skeletons was revealed using finite element analysis. This study offers insight into the future design of composite hydrogels based on the synergistic effect of soft and hard components.