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.

Spider silk is the toughest fiber found in nature, and bulk production of artificial spider silk that matches its mechanical properties remains elusive. Development of miniature spider silk proteins (mini‐spidroins) has made large‐scale fiber production economically feasible, but the fibers’ mechanical properties are inferior to native silk. The spider silk fiber's tensile strength is conferred by poly‐alanine stretches that are zipped together by tight side chain packing in β‐sheet crystals. Spidroins are secreted so they must be void of long stretches of hydrophobic residues, since such segments get inserted into the endoplasmic reticulum membrane. At the same time, hydrophobic residues have high β‐strand propensity and can mediate tight inter‐β‐sheet interactions, features that are attractive for generation of strong artificial silks. Protein production in prokaryotes can circumvent biological laws that spiders, being eukaryotic organisms, must obey, and the authors thus design mini‐spidroins that are predicted to more avidly form stronger β‐sheets than the wildtype protein. Biomimetic spinning of the engineered mini‐spidroins indeed results in fibers with increased tensile strength and two fiber types display toughness equal to native dragline silks. Bioreactor expression and purification result in a protein yield of ≈9 g L⁻¹ which is in line with requirements for economically feasible bulk scale production.

Artificial spider silk is an attractive material for many technical applications since it is a biobased fiber that can be produced under ambient conditions but still outcompetes synthetic fibers (e.g., Kevlar) in terms of toughness. Industrial use of this material requires bulk‐scale production of recombinant spider silk proteins in heterologous host and replication of the pristine fiber's mechanical properties. High molecular weight spider silk proteins can be spun into fibers with impressive mechanical properties, but the production levels are too low to allow commercialization of the material. Small spider silk proteins, on the other hand, can be produced at yields that are compatible with industrial use, but the mechanical properties of such fibers need to be improved. Here, the literature on wet‐spinning of artificial spider silk fibers is summarized and analyzed with a focus on mechanical performance. Furthermore, several strategies for how to improve the properties of such fibers, including optimized protein composition, smarter spinning setups, innovative protein engineering, chemical and physical crosslinking as well as the incorporation of nanomaterials in composite fibers, are outlined and discussed.

Silk fibres attract great interest in materials science for their biological and mechanical properties. Hitherto, the mechanical properties of the silk fibres have been explored mainly by tensile tests, which provide information on their strength, Young’s modulus, strain at break and toughness modulus. Several hypotheses have been based on these data, but the intrinsic and often overlooked variability of natural and artificial silk fibres makes it challenging to identify trends and correlations. In this work, we determined the mechanical properties of Bombyx mori cocoon and degummed silk, native spider silk, and artificial spider silk, and compared them with classical commercial carbon fibres using large sample sizes (from 10 to 100 fibres, in total 200 specimens per fibre type). The results confirm a substantial variability of the mechanical properties of silk fibres compared to commercial carbon fibres, as the relative standard deviation for strength and strain at break is 10–50%. Moreover, the variability does not decrease significantly when the number of tested fibres is increased, which was surprising considering the low variability frequently reported for silk fibres in the literature. Based on this, we prove that tensile testing of 10 fibres per type is representative of a silk fibre population. Finally, we show that the ideal shape of the stress–strain curve for spider silk, characterized by a pronounced exponential stiffening regime, occurs in only 25% of all tested spider silk fibres.

Hydrogels are useful drug release systems and tissue engineering scaffolds. However, synthetic hydrogels often require harsh gelation conditions and can contain toxic by‐products while naturally derived hydrogels can transmit pathogens and in general have poor mechanical properties. Thus, there is a need for a hydrogel that forms under ambient conditions, is non‐toxic, xeno‐free, and has good mechanical properties. A recombinant spider silk protein‐derived hydrogel that rapidly forms at 37 °C is recently developed. The temperature and gelation times are well‐suited for an injectable in situ polymerising hydrogel, as well as a 3D cell culture scaffold. Here, it is shown that the diffusion rate and the mechanical properties can be tuned by changing the protein concentration and that human fetal mesenchymal stem cells encapsulated in the hydrogels show high survival and viability. Furthermore, mixtures of recombinant spider silk proteins and green fluorescent protein (GFP) form gels from which functional GFP is gradually released, indicating that bioactive molecules are easily included in the gels, maintain activity and can diffuse through the gel. Interestingly, encapsulated ARPE‐19 cells are viable and continuously produce the growth factor progranulin, which is detected in the cell culture medium over the study period of 31 days.

Water and humidity severely affect the material properties of spider major ampullate silk, causing the fiber to become plasticized, contract, swell and undergo torsion. Several amino acid residue types have been proposed to be involved in this process, but the complex composition of the native fiber complicates detailed investigations. Here, we observe supercontraction in biomimetically produced artificial spider silk fibers composed of defined proteins. We found experimental evidence that proline is not the sole residue responsible for supercontraction and that tyrosine residues in the amorphous regions of the silk fiber play an important role. Furthermore, we show that the response of artificial silk fibers to humidity can be tuned, which is important for the development of materials for applications in wet environments, eg producing water resistant fibers with maximal strain at break and toughness modulus.