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Greco G, Schmuck B, Jalali SK, Pugno NM, Rising A. Influence of experimental methods on the mechanical properties of silk fibers: A systematic literature review and future road map. Biophys Rev (Melville) 2023; 4:031301. [PMID: 38510706 PMCID: PMC10903380 DOI: 10.1063/5.0155552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 06/20/2023] [Indexed: 03/22/2024]
Abstract
Spider silk fibers are of scientific and industrial interest because of their extraordinary mechanical properties. These properties are normally determined by tensile tests, but the values obtained are dependent on the morphology of the fibers, the test conditions, and the methods by which stress and strain are calculated. Because of this, results from many studies are not directly comparable, which has led to widespread misconceptions in the field. Here, we critically review most of the reports from the past 50 years on spider silk mechanical performance and use artificial spider silk and native silks as models to highlight the effect that different experimental setups have on the fibers' mechanical properties. The results clearly illustrate the importance of carefully evaluating the tensile test methods when comparing the results from different studies. Finally, we suggest a protocol for how to perform tensile tests on silk and biobased fibers.
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Affiliation(s)
| | | | - S. K. Jalali
- Laboratory for Bioinspired, Bionic, Nano, Meta, Materials & Mechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano, 77, 38123 Trento, Italy
| | | | - Anna Rising
- Authors to whom correspondence should be addressed: and
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Hofmaier M, Malanin M, Bittrich E, Lentz S, Urban B, Scheibel T, Fery A, Müller M. β-Sheet Structure Formation within Binary Blends of Two Spider Silk Related Peptides. Biomacromolecules 2023; 24:825-840. [PMID: 36632028 DOI: 10.1021/acs.biomac.2c01266] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Intrinsically disordered proteins (IDPs) play an important role in molecular biology and medicine because their induced folding can lead to so-called conformational diseases, where β-amyloids play an important role. Still, the molecular folding process into the different substructures, such as parallel/antiparallel or extended β-sheet/crossed β-sheet is not fully understood. The recombinant spider silk protein eADF4(Cx) consisting of repeating modules C, which are composed of a crystalline (pep-c) and an amorphous peptide sequence (pep-a), can be used as a model system for IDP since it can assemble into similar structures. In this work, blend films of the pep-c and pep-a sequences were investigated to modulate the β-sheet formation by varying the molar fraction of pep-c and pep-a. Dichroic Fourier-transform infrared spectroscopy (FTIR), circular dichroism, spectroscopic ellipsometry, atomic force microscopy, and IR nanospectroscopy were used to examine the secondary structure, the formation of parallel and antiparallel β-sheets, their orientation, and the microscopic roughness and phase formation within peptide blend films upon methanol post-treatment. New insights into the formation of filament-like structures in these silk blend films were obtained. Filament-like structures could be locally assigned to β-sheet-rich structures. Further, the antiparallel or parallel character and the orientation of the formed β-sheets could be clearly determined. Finally, the ideal ratio of pep-a and pep-c sequences found in the fibroin 4 of the major ampullate silk of spiders could also be rationalized by comparing the blend and spider silk protein systems.
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Affiliation(s)
- Mirjam Hofmaier
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069Dresden, Germany.,Chair of Physical Chemistry of Polymeric Materials, Technical University Dresden (TUD), D-01069Dresden, Germany
| | - Mikhail Malanin
- Leibniz Institute of Polymer Research Dresden (IPF), Institute of Macromolecular Chemistry, Hohe Strasse 6, D-01069Dresden, Germany
| | - Eva Bittrich
- Leibniz Institute of Polymer Research Dresden (IPF), Institute of Macromolecular Chemistry, Hohe Strasse 6, D-01069Dresden, Germany
| | - Sarah Lentz
- Chair of Biomaterials, University of Bayreuth, Prof.-Rüdiger-Bormann-Str. 1, D-95447Bayreuth, Germany
| | - Birgit Urban
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069Dresden, Germany
| | - Thomas Scheibel
- Chair of Biomaterials, University of Bayreuth, Prof.-Rüdiger-Bormann-Str. 1, D-95447Bayreuth, Germany.,Bayreuther Zentrum für Kolloide und Grenzflächen (BZKG), Universität Bayreuth, Universitätsstraße 30, D-95440Bayreuth, Germany.,Bayreuther Zentrum für Molekulare Biowissenschaften (BZMB), Universität Bayreuth, Universitätsstraße 30, D-95440Bayreuth, Germany.,Bayreuther Materialzentrum (BayMAT), Universität Bayreuth, Universitätsstraße 30, D-95440Bayreuth, Germany.,Bayerisches Polymerinstitut (BPI), Universität Bayreuth, Universitätsstraße 30, D-95440Bayreuth, Germany
| | - Andreas Fery
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069Dresden, Germany.,Chair of Physical Chemistry of Polymeric Materials, Technical University Dresden (TUD), D-01069Dresden, Germany
| | - Martin Müller
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069Dresden, Germany.,Chair of Macromolecular Chemistry, Technical University of Dresden (TUD), Mommsenstraße 4, D-01062Dresden, Germany
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Greco G, Mirbaha H, Schmuck B, Rising A, Pugno NM. Artificial and natural silk materials have high mechanical property variability regardless of sample size. Sci Rep 2022; 12:3507. [PMID: 35241705 DOI: 10.1038/s41598-022-07212-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 02/15/2022] [Indexed: 11/29/2022] Open
Abstract
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.
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