Programmable Processing toward Stiff Composite Hydrogels

To overcome the issue of the compromise between processability and mechanical property of hydrogels, a percolation-driven programmable processing method is proposed toward the preparation of plastic composite hydrogels with a high compressive modulus in a megapascal scale. The hydrogel was constructed by the incorporation of a thixotropic fluid, for example, a silica microsphere (SiMP)/sodium alginate composite, into an elastic polymer network, such as dynamically cross-linked poly(vinyl alcohol)/4-carboxyphenyl boronic acid, followed by the adjustment of interpolymer interactions. Above a threshold of SiMP content, the isolated particle lattice in the gel was interconnected by the highly entangled alginate as well as PVA chains to form a percolation double network (p-DN), leading to enhanced thixotropy to allow the processing of the hydrogel into desired shapes. Subsequently, the plasticity of the p-DN hydrogel was converted to stiffness by confining the movement of polymer chains through additional cross-linking using multivalent cationic ions. The rigidity of calcium alginate resists the dislocation of the particles in the percolation network while the elasticity of PVA holds the integrity of the hydrogel to obtain the high compressive modulus against force loading. This strategy is general to achieve processable high-performance p-DN hydrogels with varied compositions.