Soft Defect-Tolerant Material Inspired by American Lobsters

Lobster-Inspired Chitosan-Derived Adhesives with a Biomimetic Design

Polysaccharide-based adhesives, especially chitosan (CS)-derived adhesives, serve as promising sustainable alternatives to traditional adhesives. However, most demonstrate a poor adhesive strength. Inspired by the inherent layered structure of marine arthropods (lobsters), a core-shell structure (SiO2-NH2@OPG) with amine-functionalized silica (SiO2-NH2) as the core and oxidized pyrogallol (OPG) as the shell is prepared in this study. The compound is blended with CS to produce a structural biomimetic wood adhesive (SiO2-NH2@OPG/CS) with excellent performance. In addition to thermocompressive curing, this adhesive exhibits a water-evaporation-induced curing behavior at room temperature. With reference to the design mechanism of the lobster cuticle, this microphase-separated structure consists of clustered nanofibers with varying amounts of SiO2-NH2@OPG particles between the fibers. This intriguing microphase structure and its mechanical effects could offer a powerful solution for improving the functional modification of wood composites.

Transparent and Soft Crack-Resistant Bouligand Elastomers Inspired by Fish Scales

Nature with its abundant source offers numerous inspirations for structural and engineering designs. The oriented membranes stacked with bouligand structures in the fish scales show an outstanding combination of high strength and crack resistance. Although the applications of hard biomimetic composites are reported, the structures are rarely utilized in soft materials. Inspired by the scales of various fishes, electrospun membranes are used and stacked to fabricate bouligand elastomers, including orthogonal-plywood, single-bouligand, and double-bouligand structures. The effects of different structures on the properties of elastomers are systematically investigated and possible mechanism is explained using finite element analysis (FEA). The stiffness and fatigue characteristics of these biomimetic elastomers with the above structures are improved compared with the original membranes, especially the elastomers with a single-bouligand structure, which can undergo 5 000 cycles at a maximum strain of 35% without complete failure. The crack only propagates to half of the width of the elastomer with remaining strength of 50% of its original strength. Moreover, the mechanical performance can be adjusted by regulating the proportion of the components. The excellent crack-resistant properties and transparency promote its various potential applications.

Toughness Amplification via Controlled Nanostructure in Lightweight Nano-Bouligand Materials

The enhanced properties of nanomaterials make them attractive for advanced high-performance materials, but their role in promoting toughness has been unclear. Fabrication challenges often prevent the proper organization of nanomaterial constituents, and inadequate testing methods have led to a poor knowledge of toughness at small scales. In this work, the individual roles of nanomaterials and nanoarchitecture on toughness are quantified by creating lightweight materials made from helicoidal polymeric nanofibers (nano-Bouligand). Unidirectional ( θ $\theta $  = 0°) and nano-Bouligand beams ( θ $\theta $  = 2°-90°) are fabricated using two-photon lithography and are designed in a micro-single edge notch bend (µ-SENB) configuration with relative densities ρ ¯ $\overline \rho $ between 48% and 81%. Experiments demonstrate two unique toughening mechanisms. First, size-enhanced ductility of nanoconfined polymer fibers increases specific fracture energy by 70% in the 0° unidirectional beams. Second, nanoscale stiffness heterogeneity created via inter-layer fiber twisting impedes crack growth and improves absolute fracture energy dissipation by 48% in high-density nano-Bouligand materials. This demonstration of size-enhanced ductility and nanoscale heterogeneity as coexisting toughening mechanisms reveals the capacity for nanoengineered materials to greatly improve mechanical resilience in a new generation of advanced materials.

High-Performance Crack-Resistant Elastomer with Tunable "J-Shaped" Stress-Strain Behavior Inspired by the Brown Pelican

The gular sac tissue of brown pelican featured by the curvy pattern of fibers has an excellent combination of strain-stiffening behavior and fracture resistance. We develop an embroidery-reinforcement and solvent-welding strategy to fabricate a biomimetic elastomer with similar structure to that of the gular sac tissue. The embroidery reinforcement enables a well-designed biomimetic pattern of aramid fibers, and the solvent welding induces strong interfacial interaction between the aramid fibers and polyurethane matrix. This strategy endows the composite with excellent strain-stiffening behavior, fracture resistance, mechanical strength, and toughness, which are even better than the living prototype. Finite elements analysis reveals that the curvy pattern and strong interfacial interaction are crucial for both the J-shape behavior and the mechanical properties. The facile and robust strategy can be extended to other fibers reinforced polymers and should be promising for development of strong and tough soft materials with "J-shape" behavior.

Toughening Mechanism of Unidirectional Stretchable Composite

Composite materials have been long developed to improve the mechanical properties such as strength and toughness. Most composites are non-stretchable which hinders the applications in soft robotics. Recent papers have reported a new design of unidirectional soft composite with superior stretchability and toughness. This paper presents an analytical model to study the toughening mechanism of such composite. We use the Gent model to characterize the large deformation of the hard phase and soft phase of the composite. We analyze how the stress transfer between phases deconcentrates the stress at the crack tip and enhances the toughness. We identify two types of failure modes: rupture of hard phase and interfacial debonding. We calculate the average toughness of the composite with different physical and geometric parameters. The experimental results in literature agree with our theoretical predictions very well.