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1. The transcriptome of Darwin’s bark spider silk glands predicts proteins contributing to dragline silk toughness

   https://doi.org/10.1038/s42003-019-0496-1  

   Garb, Jessica E. ; Haney, Robert A. ; Schwager, Evelyn E. ; Gregorič, Matjaž ; Kuntner, Matjaž ; Agnarsson, Ingi ; Blackledge, Todd A. ( July 2019 , Communications Biology)

   Darwin’s bark spider (Caerostris darwini) produces giant orb webs from dragline silk that can be twice as tough as other silks, making it the toughest biological material. This extreme toughness comes from increased extensibility relative to other draglines. We showC. darwinidragline-producing major ampullate (MA) glands highly express a novel silk gene transcript (MaSp4) encoding a protein that diverges markedly from closely related proteins and contains abundant proline, known to confer silk extensibility, in a unique GPGPQ amino acid motif. This suggestsC. darwinievolved distinct proteins that may have increased its dragline’s toughness, enabling giant webs.Caerostris darwini’sMA spinning ducts also appear unusually long, potentially facilitating alignment of silk proteins into extremely tough fibers. Thus, a suite of novel traits from the level of genes to spinning physiology to silk biomechanics are associated with the unique ecology of Darwin’s bark spider, presenting innovative designs for engineering biomaterials.

    

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2. Bioinspired Tough and Strong Fibers with Hierarchical Core–Shell Structure

   https://doi.org/10.1002/admi.202201962  

   Xiao, Yao ; Yang, Chenjing ; Zhai, Xiaowei ; Zhao, Lai ; Zhao, Peng ; Ruan, Jian ; Chen, Dong ; Weitz, David A. ; Liu, Kai ( January 2023 , Advanced Materials Interfaces)

   Strong and tough bio‐based fibers are attractive for both fundamental research and practical applications. In this work, strong and tough hierarchical core–shell fibers with cellulose nanofibrils (CNFs) in the core and regenerated silk fibroins (RSFs) in the shell are designed and prepared, mimicking natural spider silks. CNF/RSF core–shell fibers with precisely controlled morphology are continuously wet‐spun using a co‐axial microfluidic device. Highly‐dense non‐covalent interactions are introduced between negatively‐charged CNFs in the core and positively‐charged RSFs in the shell, diminishing the core/shell interface and forming an integral hierarchical fiber. Meanwhile, shearing by microfluidic channels and post‐stretching induce a better ordering of CNFs in the core and RSFs in the shell, while ordered CNFs and RSFs are more densely packed, thus facilitating the formation of non‐covalent interactions within the fiber matrix. Therefore, CNF/RSF core–shell fibers demonstrate excellent mechanical performances; especially after post‐stretching, their tensile strength, tensile strain, Young's modulus, and toughness are up to 635 MPa, 22.4%, 24.0 GPa, and 110 MJ m⁻³, respectively. In addition, their mechanical properties are barely compromised even at −40 and 60 °C. Static load and dynamic impact tests suggest that CNF/RSF core–shell fibers are strong and tough, making them suitable for advanced structural materials.

    

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3. Poly(vinyl alcohol) Hydrogels with Broad‐Range Tunable Mechanical Properties via the Hofmeister Effect

   https://doi.org/10.1002/adma.202007829  

   Wu, Shuwang ; Hua, Mutian ; Alsaid, Yousif ; Du, Yingjie ; Ma, Yanfei ; Zhao, Yusen ; Lo, Chiao‐Yueh ; Wang, Canran ; Wu, Dong ; Yao, Bowen ; et al ( February 2021 , Advanced Materials)

   Hydrogels, exhibiting wide applications in soft robotics, tissue engineering, implantable electronics, etc., often require sophisticately tailoring of the hydrogel mechanical properties to meet specific demands. For examples, soft robotics necessitates tough hydrogels; stem cell culturing demands various tissue‐matching modulus; and neuron probes desire dynamically tunable modulus. Herein, a strategy to broadly alter the mechanical properties of hydrogels reversibly via tuning the aggregation states of the polymer chains by ions based on the Hofmeister effect is reported. An ultratough poly(vinyl alcohol) (PVA) hydrogel as an exemplary material (toughness 150 ± 20 MJ m⁻³), which surpasses synthetic polymers like poly(dimethylsiloxane), synthetic rubber, and natural spider silk is fabricated. With various ions, the hydrogel's various mechanical properties are continuously and reversibly in situ modulated over a large window: tensile strength from 50 ± 9 kPa to 15 ± 1 MPa, toughness from 0.0167 ± 0.003 to 150 ± 20 MJ m⁻³, elongation from 300 ± 100% to 2100 ± 300%, and modulus from 24 ± 2 to 2500 ± 140 kPa. Importantly, the ions serve as gelation triggers and property modulators only, not necessarily required to remain in the gel, maintaining the high biocompatibility of PVA without excess ions. This strategy, enabling high mechanical performance and broad dynamic tunability, presents a universal platform for broad applications from biomedicine to wearable electronics.

    

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4. Effects of terminal tripeptide units on mechanical properties of collagen triple helices

   https://doi.org/10.1016/j.eml.2023.102075  

   Masrouri, Milad ; Qin, Zhao ( November 2023 , Extreme Mechanics Letters)

   Collagen, a vital protein that provides strength to various body tissues, has a triple helix structure containing three polypeptide chains. The chains are composed mostly of a tripeptide of glycine (G), proline (P), and hydroxyproline (O). Using molecular dynamics simulations and theoretical analysis, the study examines the mechanical response of collagen triple helix structures, made up of three different tripeptide units, when subjected to different fracture loading modes. The results show that collagen with GPO tripeptide units at their C-terminal are mechanically stronger than the POG and OGP units with a single amino-acid frame shift. Our work shows that the N-terminal has less effect on collagen fracture than the C-terminal. The differences in mechanical response are explained by the heterogenous rigidity of the amino acid backbone and the resulting shear lag effect near the terminal. The findings have potential applications in developing tough synthetic collagen for building materials and may stimulate further studies on the connection between terminal repeats and the mechanical-thermal behavior of other structural proteins such as silk, elastin, fibrin, and keratin. 

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5. Bi-terminal fusion of intrinsically-disordered mussel foot protein fragments boosts mechanical strength for protein fibers

   https://doi.org/10.1038/s41467-023-37563-0  

   Li, Jingyao ; Jiang, Bojing ; Chang, Xinyuan ; Yu, Han ; Han, Yichao ; Zhang, Fuzhong ( April 2023 , Nature Communications)

   Microbially-synthesized protein-based materials are attractive replacements for petroleum-derived synthetic polymers. However, the high molecular weight, high repetitiveness, and highly-biased amino acid composition of high-performance protein-based materials have restricted their production and widespread use. Here we present a general strategy for enhancing both strength and toughness of low-molecular-weight protein-based materials by fusing intrinsically-disordered mussel foot protein fragments to their termini, thereby promoting end-to-end protein-protein interactions. We demonstrate that fibers of a ~60 kDa bi-terminally fused amyloid-silk protein exhibit ultimate tensile strength up to 481 ± 31 MPa and toughness of 179 ± 39 MJ*m⁻³, while achieving a high titer of 8.0 ± 0.70 g/L by bioreactor production. We show that bi-terminal fusion of Mfp5 fragments significantly enhances the alignment of β-nanocrystals, and intermolecular interactions are promoted by cation-π and π-π interactions between terminal fragments. Our approach highlights the advantage of self-interacting intrinsically-disordered proteins in enhancing material mechanical properties and can be applied to a wide range of protein-based materials.

    

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