Stiffness and toughness of soft/stiff suture joints in biological composites

Biological composites can overcome the conflict between strength and toughness to achieve unprecedented mechanical properties in engineering materials. The suture joint, as a kind of heterogeneous architecture widely existing in biological tissues, is crucial to connect dissimilar components and to attain a tradeoff of all-sided functional performances. Therefore, the suture joints have attracted many researchers to theoretically investigate their mechanical response. However, most of the previous models focus on the sutural interface between two chemically similar stiff phases with (or without) a thin adhesive layer, which are under the framework of linear elasticity and small deformation. Here, a general model based on the finite deformation framework is proposed to explore the stiffness and toughness of chemically dissimilar suture joints connecting soft and stiff phases. Uniaxial tension tests are conducted to investigate the tensile response of the suture joints, and finite element simulations are implemented to explore the underlying mechanisms, considering both material nonlinearity and cohesive properties of the interface. Two failure modes are quantitively captured by our model. The stored elastic energy in the soft phase competes with the energy dissipation due to the interface debonding, which controls the transition among different failure modes. The toughness of the suture joints depends on not only the intrinsic strengths of the constituent materials and their cohesive strength, but also the interfacial geometry. This work provides the structure-property relationships of the soft/stiff suture joints and gives a foundational guidance of mechanical design towards high-performance bioinspired composites.