Characterization of natural and biomimetic spider silk fibers

Abstract

List of notations FS= forced silking RH = relative humidity % w/v = weight per volume percentage % v/v = volume per volume percentage IntroductionSpider silk produced by orb-weaving spiders reveals fascinating mechanical properties, in particular, its unique combination of high tensile strength and elasticity, distinguishing it from most other natural or man-made fi bers (Cunniff et al., 1994;Denny, 1976;Eisoldt et al., 2011;Gosline et al., 1984Gosline et al., , 1999Heim et al., 2009;Kaplan et al., 1991;Ko and Jovicic, 2004). Of the fi ve different silks produced by an orb-weaving spider for web building, dragline silk, serving as frame and radial fi ber in the web and as the spider's lifeline, is the best characterized one, as it is the easiest accessible one Vollrath, 2000). A common method to obtain dragline silk for mechanical and structural analysis is the application of forced silking of captive spiders, that is, forcibly pulling the fi ber from a spider's spinneret (e.g. by winding it on a rotating mandrel) (Ortlepp and Gosline, 2004;Perez-Rigueiro et al., 2005;Work and Emerson, 1982). Earlier studies have revealed that spinning speeds have an impact on resilience, strain at breaking, breaking energy, initial Young's modulus, yield point and ductility (most likely related to the variation in diameter of a single fi ber; Chen et al., 2006; PerezRigueiro et al., 2005;Romer and Scheibel, 2008;Scheibel, 2004;). Furthermore, it was shown that forcibly silked fi bers have higher storage moduli and lower loss moduli than native silks (Blackledge et al., 2005; Work, 1976). Despite their intriguing mechanical properties, the use of these fi bers in various industrial or medical applications is limited because of constraints in farming of spiders which are based on their territorial and cannibalistic nature (Fox, 1975). Thus, the focus of silk research has recently shifted towards biotechnologically producing the underlying proteins as well as mimicking the spinning process to produce a new class of high-performance fi bers (Hardy et al., 2008;O'Brien et al., 1998;Omenetto and Kaplan, 2010;Scheibel, 2004).Artifi cial spider silk fi bers can be obtained by two different approaches: (a) spinning from regenerated silk dopes and (b) spinning from solutions of recombinant silk proteins. Regenerated silk solutions from silk fi bers are usually prepared by dissolving a large amount of natural silk fi bers in harsh solvents, such as highly concentrated lithium bromide solutions, hexafl uoroisopropanol (HFIP) or hexafl uoroacetone hydrate (Hardy et al., 2008). However, the number of studies on spider silk is limited as most Pages 83-94 http://dx

Dragline, Egg Stalk and Byssus: A Comparison of Outstanding Protein Fibers and Their Potential for Developing New Materials

“…As with B. mori silk, processing affects the mechanical properties of spider dragline silk. In forced silking experiments, higher reeling speeds led to higher modulus and tensile strength and lower elongation, presumably due to greater alignment of silk molecules 36–39. In the case of naturally spun dragline silk, there is considerable variability in mechanical properties both within a species and between threads from a single individual.…”

“…Like B. mori silk, spider dragline silk can be considered a composite material of crystalline β‐sheet regions embedded in an amorphous matrix (see Figure ), but the degree of crystallinity differs at 40–55% for B. mori vs. 11–30% for N. clavipes spider dragline silk7, 46 and 34–35% for A. diadematus. 36 Moreover, β‐sheet crystallites are more aligned along the thread axis in spider silk. It is also worth mentioning that there are differences between the hierarchical structure of B. mori and spider dragline silks.…”

“…When wetted or exposed to humidity above 60%, water interpenetrates dragline silk and disrupts hydrogen bonds, allowing a rearrangement of peptide chains to configurations of higher entropy 53. This process is termed supercontraction, as it causes dramatic shrinkage (up to 50%)54 of unattached threads and changes their material properties to rubber‐like as long as they are wet 36, 55. Threads under tension, as found in webs, show less change in material properties but develop considerable stress.…”

Detection of Chlorpyrifos Using Bio-Inspired Silver Nanograss

“…For example, the most familiar example of biomimicry in daily life is Velcro, which was modeled on the seeds of Serrata. Moreover, waterproof paint from the lotus leaf effect, artificial fibers from the spider silk, adhesive surface from the gecko foot surface, and adhesive materials in water from mussels are famous examples of bio-inspired technology [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. As a part of biomimetic technology, we previously developed an artificial microfiber that mimicked a spider’s web and nano pine pollen that mimicked pine pollen [ 10 , 11 ].…”

Bioinspired materials: An emerging field of multidisciplinary research

“…The obtained results from the natural system are reported to have a great potential to improve joints in braided fiber-reinforced composites, which will result into the future development of a fully automated fabrication of biomimetic branched composites. Keerl et al (2012) introduce the reader into the fascinating mechanical properties of spider silk produced by orb-weaving spiders. They analyzed the mechanical characteristics of dragline silk fibers of Araneus diadematus and compared the obtained values to artificially produced fibers of a recombinant silk protein.…”