Spider silks are among the toughest known materials and thus provide models for renewable, biodegradable, and sustainable biopolymers. However, the entirety of their diversity still remains elusive, and silks that exceed the performance limits of industrial fibers are constantly being found. We obtained transcriptome assemblies from 1098 species of spiders to comprehensively catalog silk gene sequences and measured the mechanical, thermal, structural, and hydration properties of the dragline silks of 446 species. The combination of these silk protein genotype-phenotype data revealed essential contributions of multicomponent structures with major ampullate spidroin 1 to 3 paralogs in high-performance dragline silks and numerous amino acid motifs contributing to each of the measured properties. We hope that our global sampling, comprehensive testing, integrated analysis, and open data will provide a solid starting point for future biomaterial designs.

Many roads to being tough: A number of routes exist to increase toughness in both natural and human-made materials—for example, using secondary phases and precipitates or exploiting tailored architectures and shaped crystals. Polishchuk et al. detail the nanoscale internal structure of calcitic microlenses formed by a brittlestar (see the Perspective by Duffy). The segregation of magnesium-rich particles forms a secondary phase that places compressive stresses on the host matrix. This toughening mechanism resembles Guinier-Preston zones known in classical metallurgy. Science , this issue p. 1294 see also p. 1254

Three-dimensional (3D) assemblies based on carbon nanomaterials still lag behind their individual one-dimensional building blocks in terms of mechanical and electrical properties. Here we demonstrate a simple strategy for the fabrication of an open porous 3D self-organized double-hierarchical carbon nanotube tube structure with properties advantageous to those existing so far. Even though no additional crosslinking exists between the individual nanotubes, a high reinforcement effect in compression and tensile characteristics is achieved by the formation of self-entangled carbon nanotube (CNT) networks in all three dimensions, employing the CNTs in their high tensile properties. Additionally, the tubular structure causes a self-enhancing effect in conductivity when employed in a 3D stretchable conductor, together with a high conductivity at low CNT concentrations. This strategy allows for an easy combination of different kinds of low-dimensional nanomaterials in a tube-shaped 3D structure, enabling the fabrication of multifunctional inorganic-carbon-polymer hybrid 3D materials.

Hierarchical structures with constituents over multiple length scales are found in various natural materials like bones, shells, spider silk and others, all of which display enhanced quasistatic mechanical properties, such as high specific strength, stiffness, and toughness. At the same time, the role of hierarchy on the dynamic behavior of metamaterials remains largely unexplored. This study numerically and experimentally assesses the effect of bioinspired hierarchical organization as well as of viscoelasticity on the wave attenuation properties of continuous elastic metamaterials. We consider single-phase metamaterials formed by self-similar unit cells with different hierarchical levels and types of hierarchy. Two types of structures are considered: a hub-spoke geometry with thin connecting elements and nested hierarchical organization, and a crosslike porous geometry with external hierarchical organization. In the first, hierarchical elements occur at similar size scales, while in the second they differ by one order of magnitude. Results highlight a number of advantages through the introduction of structural hierarchy. Band gaps relative to the corresponding nonhierarchical structures are mostly preserved in both types of structures, but additional hierarchically-induced band gaps also appear, and the hierarchical configuration allows the tuning of band-gap frequencies to lower frequencies in the crosslike porous geometry, with a simultaneous significant reduction of the global structural weight. We show that even small viscoelastic effects are essential in determining the overall attenuation behavior, including between band gaps. Finally, we verify the numerically-predicted multifrequency band gaps by experimental characterization of the transmission properties of crosslike structures. The approach we propose allows the incorporation of hierarchical organization in existing metamaterial configurations, with the corresponding improvement of wave-damping properties, thus extending application possibilities for elastic metamaterials to multiple frequency scales.