Biopolymer-like Stress-Stiffening in Soft Composites with a Near-Jamming Filler Network

Soft gels embedded with micron-sized filler particles constitute soft composites with wide-ranging applications. The included particles can imbue the gel matrix with highly nonlinear mechanical features [1]. For example, previous studies have shown that particle inclusions below jamming in biopolymer networks can alter the global stress response from compression softening to compression stiffening. However, due to the inherent hierarchical and amorphous nature of dense composites, the influence of a near-jamming filler network on composite mechanics remains unclear.

In this work, we experimentally demonstrate that a near-jamming filler network transforms a linear silicone gel into a nonlinear composite that stiffens as strongly as certain types of biopolymer networks. In particular, we observed a power-law relationship between the shear modulus and shear stress with an exponent near 3/2, similar to reconstituted biopolymer networks and biomimetic gels. Our study shows that this exponent remains robust across a wide range of material parameters, while appearing sensitive to the structure of the near-jamming filler network. The findings uncover the structural origin of stress-stiffening in dense soft composites, and suggest a new design paradigm for engineering biomimetic responses in soft materials.