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The prevailing models of spider silk structure. (A) is reproduced with permission from ref. 16, and considers spider silk to be a network of rubber- like chains reinforced by b -sheet crystals. This model fits closely to mechanical data but not to structural studies. (B) shows a glassy structure, reproduced with permission from ref. 14, based on their NMR findings. Although this model shows the presence and possible distribution of secondary structures, we are yet to establish how they interact. The molecular structure shown here consists of b -sheet regions, containing alanine (red lines) and glycine (blue lines), interleaved with predominantly 3 1 -helical parts (blue curls), which do not contain alanine. (C), reproduced with permission from ref. 11, has a simplified interpretation of structure, showing a series of beads with varying degrees of order, as defined by the level of hydrogen bonding between the folds.
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Spider silk shows great potential as a biomaterial: in addition to biocompatibility and biodegradability, its strength and toughness are greater than native biological fibres (e.g. collagen), with toughness exceeding that of synthetic fibres (e.g. nylon). Although the ultimate tensile strength and toughness at failure are unlikely to be limiting fa...
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... hydrophilic Spidroin II. 12,13 The combination of these proteins can be simplified into 40% ordered domains (two hydrogen bonds per amide group), 15% permanently disordered domains (one hydrogen bond per amide group) and 45% intrinsically disordered domains which have a potential for order. 11 These domains predominantly occur in b -sheet, a -helical and pseudo-amorphous chain configurations 14 to form a complex, glassy polymer (see Fig. 2b). The central problem in spider silk mechanics, however, is not identifying the constituents, but understanding how they interact to confer silk’s exceptional mechanical properties. A number of models have been proposed to describe these interactions 11,14,15,16 (Fig. 2), yet detailed structure–function relationships remain elusive. Based on the prevailing models and the established understanding of structure, 14–16 we can conceive a number of phenomena occurring during elastic deformation. The disordered domains, though predominantly glassy and under pre-tension, will show a very small degree of ‘lock-in’ as they align with the direction of applied stress, pull the b -sheets into alignment, 17 and thus decrease the entropy of the system. Under sufficient stress these less-ordered structures will break their hydrogen bonds in series and reconfigure. Cooperative hydrogen bond rupture is unlikely to occur in the disordered domains, allowing local ‘plastic’ deformation at stresses corresponding to the energy required to rupture individual bonds 18,19 which when grouped together, possess a combined cohesive energy of 42 kJ mol À 1 in a disordered domain compared to 52 kJ mol À 1 in an ordered domain, based on calculations for poly(alanine) using 10 kJ mol À 1 per hydrogen bond, due to fewer bonds. 15 In these more-ordered b -sheet and helical structures, the entropic elasticity of the protein backbone and related cooperative rupture of hydrogen bonds provide an intrinsic strength and local elasticity, which allows them to withstand up to three or four times the stress required to break a single bond. 18 After yield, the glassy characteristics are thought to give way to a rubber-like behaviour. 11 Despite the vague understanding of the structure–function relationships, it has already been suggested that by controlling and/or reinforcing the nanoscale folding structure, a new class of super-tough materials may be within reach. 11,20 Proline 21 and glycine 22 content, and the speed of spinning 23 have been shown to affect the mechanical characteristics of spider silk by controlling the structure on this level. A recent article by Lee et al. 24 showed that the stiffness, extensibility, strength, and therefore toughness can be increased substantially by infiltrating metal impurities into the secondary and tertiary structure. This was achieved through multiple pulsed vapour-phase infiltration of zinc, tita- nium, or aluminium. Long-term exposure to the precursor vapour was argued to lead to the infiltration of Al 3+ , Ti 4+ , or Zn 2+ to create metal–protein complexes with metal-coordinated or covalent bonds. Although the high stiffness resulting from this particular modification may be detrimental for many biomedical applications due to stress shielding effects, 25,26 the study provides an interesting insight into the methods by which spider silk could be modified to become a more effective biomaterial. This leads to consider the mechanisms involved in yield, and particularly how yield can potentially be extended to allow higher strains while maintaining its elastic modulus (Fig. 3), which is possibly the best mechanical feature of spider silk for biomaterial applications as it has the potential to replace ‘native’ fibres such as collagen and elastin in tissue constructs. The controllable stiffness, in addition to its desirable chemistry and morphology, may also be useful in directing biological responses. 27,28 Several theories describe the mechanism of yield in glassy polymers. Although these assume a simpler structural configuration than that of silk, they show that both intra- 29 and inter- molecular 30 processes are important, with inter-molecular processes being dominant at temperatures more than 80 K below the glass transition point. 31 From this classical perspective, inter- molecular processes are likely to be more important for biomedical applications, as physiological temperature (310 K) is far below the glass transition point of spider silk (471 K). 32 Recent spider silk-specific models, 15 however, have predicted that yield may be related to a mechanically induced glass transition, with a local strain energy equivalent to the thermal energy required to break hydrogen bonds and would be likely to involve both inter- and intra-molecular processes. The concept of a mechanically rather than thermally driven transition is similar to the transition points in a classical phase diagram, which involve a combination of ‘pressure’ ( i.e. mechanical stimulus) and temperature. Based on these interpretations, it can be reasonably postulated that yield in spider silk occurs as the conformation changes and the disordered domains in the material dissipate elastic energy by breaking hydrogen bonds. By breaking the bonds in the disordered domains, essentially freeing the protein chains, the material reverts to a reinforced rubber type structure 11 that allows large post-yield deformation. The question remains, however, of how the yield strain can be increased. Lee et al. 24 (Fig. 4) propose, based on Termonia’s model 16 (Fig. 2A) that the overall increase in extensibility they observed in infiltrated fibres was due to an increased proportion of rubber-like amorphous domains, ...
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The unique properties of spider silk such as strength, extensibility, toughness, biocompatibility and biodegradability are the reasons for the recent development in silk biomaterial technology. For a long time scientific progress was impeded by limited access to spider silk. However, the development of the molecular biology strategy was a breaking...
Repair success for injuries to the flexor tendon in the hand is often limited by the in vivo behaviour of the suture used for repair. Common problems associated with the choice of suture material include increased risk of infection, foreign body reactions, and inappropriate mechanical responses, particularly decreases in mechanical properties over...
We measure the elastic stiffnesses of the concentrated viscous protein solution of the dehydrated Nephila clavipes major ampullate gland with Brillouin light scattering. The glandular material shows no rigidity but possesses a tensile stiffness similar to that of spider silk. We show, however, that with application of a simple static shear, the mec...
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... In contrast to B. mori silk, spider silk does not comprise any sericin. [76][77][78][79][80] Moreover, it is biocompatible and has a very high strength-to-density ratio, exceeding the one of high-performance steels and many commercial fibers. 81 Unlike silkworms, which rely on two essential proteins-sericin and fibroin-spiders manufacture proteins (spidroins) whose composition and properties vary significantly between species. ...
Intervertebral disc (IVD) degeneration (IDD) is the main contributor to chronic low back pain. To date, the present therapies mainly focus on treating the symptoms caused by IDD rather than addressing the problem itself. For this reason, researchers have searched for a suitable biomaterial to repair and/or regenerate the IVD. A promising candidate to fill this gap is silk, which has already been used as a biomaterial for many years. Therefore, this review aims first to elaborate on the different origins from which silk is harvested, the individual composition, and the characteristics of each silk type. Another goal is to enlighten why silk is so suitable as a biomaterial, discuss its functionalization, and how it could be used for tissue engineering purposes. The second part of this review aims to provide an overview of preclinical studies using silk‐based biomaterials to repair the inner region of the IVD, the nucleus pulposus (NP), and the IVD's outer area, the annulus fibrosus (AF). Since the NP and the AF differ fundamentally in their structure, different therapeutic approaches are required. Consequently, silk‐containing hydrogels have been used mainly to repair the NP, and silk‐based scaffolds have been used for the AF. Although most preclinical studies have shown promising results in IVD‐related repair and regeneration, their clinical transition is yet to come. For years, researchers have been seeking a suitable biomaterial to repair and/or regenerate the intervertebral disc (IVD) and a promising candidate to fill this gap could be the application of silk. Therefore, this review aims to elaborate on the different origins from which silk is harvested, the characteristics of each silk type and how it can be used for tissue engineering purposes. Moreover, the review provides an overview of preclinical studies that have used silk‐based biomaterials to repair the inner region of the IVD, the nucleus pulposus, as well as the IVD's outer region, the annulus fibrosus.
... The spider silk-based metal-dielectric-coated optical fiber is promising for plasmonic applications. Furthermore, the homogenous quality of the spider silk-based optical fiber with metal coating can be confirmed by performing tensile tests [37]. Figure 2(a) shows the tensile testing machine (Hung-Ta HT-2402) used to test the strength and elasticity of the fabricated spider silk-based fiber. ...
Various optical components employed in biomedical applications have been fabricated using spider silk because of its superior properties, such as elasticity, tensile strength, biodegradability, and biocompatibility. In this study, a highly sensitive fiber optic sugar sensor is fabricated using metal-nanolayer-coated spider silk. The spider silk, which is directly collected from Nephila pilipes, a giant wood spider, is naturally a protein-based biopolymer with great flexibility, low attenuation, and easy functionalization. The surface of the spider silk-based fiber is coated with a metal nano-layer by using the glancing angle deposition technique. This fiber optic sugar sensor is based on the principle of the change in the refractive indices of sugar solutions. The attained experimental results show that the proposed sugar sensor is highly sensitive in the detection of fructose, sucrose, and glucose concentrations. This work may provide a new way to realize precise and sensitive online sugar measurements for point-of-care diagnostics.
... 28,29 Dressilk, which consists of a natural material, was already shown to be antiinfective. 12,[30][31][32][33][34][35] Additionally, Ju et al were able to show in a burn rat model that silk fibroin significantly reduces the expression of the pro-inflammatory cytokine IL-1α. 36 Because of these properties, a number of antibacterial wound dressings are based on silk fibroin. ...
Currently, many dressings are commercially available for the treatment of burn wounds. Some of these wound dressings remain on the wound, prevent painful dressing changes, and reduce tissue scarring. Nevertheless, still a wound dressing that is cost‐effective, produces good wound healing properties, and has a high patient satisfaction is needed. Standard care of superficial burn wounds differs between burn centres. This study aimed to determine a dressing with easy appliance, accurate pain control, favourable outcome, and cost‐effectiveness. Therefore, we compared the widely used but expensive Suprathel with the rather new but much cheaper Dressilk in the clinical setting. In a prospective clinical study, the healing of partial thickness burn wounds after simultaneous treatment with Suprathel and Dressilk was examined in 20 patients intra‐individually. During wound healing, pain, infection, exudation, and bleeding were evaluated. A subjective scar evaluation was performed using the Patient and Observer Scar Scale. Both dressings were easy to apply, remained on the wound in place, and were gradually cut back as reepithelisation proceeded and showed similar times to wound closure. Dressing changes were not necessary, and neither infections nor bleeding was detected. Overall exudation and pain were highest in the beginning but declined during the wound‐healing phase without significant differences. In the follow‐up scar evaluation after 12 months, patients reported overall high satisfaction. Overall, the modern dressings Suprathel and Dressilk (solely made out of pure silk) led to safe wound healing without infection and rapidly reduced pain. There was no need for dressing changes, and they had similar clinical outcomes in scar evaluation. Therefore, both dressings seem to be ideal for the treatment of superficial burns. Because acquisition costs remain one of the main factors in the treatment of burns, Dressilk, which is ~20 times cheaper than Suprathel, remains a good option for the treatment of partial thickness burns.
... Molecular dynamics simulation studies of repetitive domains and studies using X-ray diffraction, and NMR and FTIR spectroscopy on native silk fibers show that it is mainly the glycine rich amorphous regions of the fiber that are affected when the fiber supercontract 29,[42][43][44][45][46][47][48]51,[63][64][65][66][67] . Water molecules are suggested to enter the fiber, breaking interchain hydrogen bonds that cause the amorphous regions to contract 45,47,68,69 . ...
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. Exposing spider silk to wet conditions can cause supercontraction. Here, tyrosine amino acid residues within the amorphous regions are found to contribute to supercontraction, which can be controlled by protein engineering.
... recombinant spider silk particles as drug delivery vehicles [3] . According to Brown [4] constant drug release rate could be realised for a period of two weeks using spider silk, and concluded that spider silk particles have high potential to be used for diverse applications when there is a requirement for controlled release from biodegradable carriers. Spider silk has also been suggested to be used as a load bearing biomaterial by Brown [4] because of its strength and torsionality. ...
... According to Brown [4] constant drug release rate could be realised for a period of two weeks using spider silk, and concluded that spider silk particles have high potential to be used for diverse applications when there is a requirement for controlled release from biodegradable carriers. Spider silk has also been suggested to be used as a load bearing biomaterial by Brown [4] because of its strength and torsionality. ...
Antimicrobial activity of web of spider Nephila pilipes was studied on two different bacteria. Web extract prepared in three different solvents Ethanol, Methanol and Acetone. Zone of inhibition was observed for two bacteria E. coli and S. aureus after 24 hours, for all solvents. Web extract in Ethanol has shown inhibition zone of diameter 10 mm for E.coli and no antimicrobial activity for S. aureus. Methanol extract shown zone of inhibition 18 mm for E. coli and 14 mm for S. aureus. For Acetone it was 14 mm for E. coli and 16 mm for S. aureus.
... [1][2][3][4] Those fibrous proteins contain typical rigid domains, such as b-sheet or a-helix, and flexible structures that are determined by amorphous domains. [5,6] The b-sheet nanocrystals that are interconnected by supramolecular interactions (for example, hydrogen bonds) universally consist of highly conserved poly-(Gly/Ala) and poly-Ala domains, which endow the silk with high breaking strength and modulus (stiffness). On the other hand, the hydrophilic domains, which consist of poly-Pro/Gly, are mainly respon- ...
... b-sheet 284 AE 88 34.2 AE 12.5 4.1 AE 0.6 61 AE 33 Regenerated silk fibroin [28] b-sheet % 200 % 25 -% 34 Regenerated silk fibroin [32] b-sheet 133 AE 35 8.1 AE 5.3 11 AE 3 8.8 AE 5.0 Argiope trifasciata (spider) [30] b-sheet % 342 % 54 % 8.5 % 148 MaSp1 and MaSp2 [33] b-sheet 221.7 AE 11.0 56 AE 7 6 AE 0.5 102.5 AE 13.6 NT2RepCT [34] b-sheet 162 AE 8 3 7 AE 5 6 AE 0.8 45 AE 7 Protein-like multi-block copolymers(HA x B y ) [35] b-sheet % 23 % 6 % 0.5 -Hagfish slime thread [27] b-sheet 153. 6 [36] a-helix 151 AE 31 20.5 AE 1.95 0.89 AE 0.15 -Virus protein [39] Micro-sized rod % 33 % 1.3 % 3.0 - ...
Proteins used for the formation of light weight and mechanically strong biological fibers are typically composed of folded rigid and unfolded flexible units. In contrast to fibrous proteins, globular proteins are generally not regarded as a good candidate for fiber production due to their intrinsic structural defects. Thus, it is challenging to develop an efficient strategy for the construction of mechanically strong fibers using spherical proteins. Herein, we demonstrate the production of robust protein fibers from bovine serum albumin (BSA) using a microfluidic technique. Remarkably, the toughness of the fibers was up to 143 MJ m⁻³, and after post‐stretching treatment, their breaking strength increased to almost 300 MPa due to the induced long‐range ordered structure in the fibers. The performance is comparable to or even higher than that of many recombinant spider silks or regenerated silkworm fibers. Thus, this work opens a new way for making biological fibers with high performance.
... Silk is a natural protein fiber that is used by certain insects such as spiders and silkworms (Bombyx mori), with the former using it to make webs and the latter to form cocoons. Though spider silk is known for its outstanding mechanical properties [16], Bombyx mori silk from domesticated silkworms has the advantage of being available in higher quantities [17]. The latter is composed of two main proteins, sericin and fibroin. ...
... While the ATR-FTIR spectra of C p and C s are quite similar, still there are slight differences, such as the shoulder at 1695 cm -1 in C p and the amide I band at 1650 cm -1 for C s . This can be attributed to C p polypeptides being composed of the crystalline regions of silk fibroin and having a β-sheet type structure, while C s has an α-helix type structure [16,23]. The spectra for C p (see Fig 1A) exhibit a shoulder on the amide I band at 1695 cm -1 that is typically associated with a β-sheet structure of SF, as well as Amide I, II and III absorptions at 1622, 1515 and 1230 cm -1 that are characteristic of SF [27,59]. ...
Silk fibroin-derived polypeptides (FDPs) are polypeptides resulting from the enzymatic separation of the hydrophobic crystalline (Cp) and hydrophilic electronegative amorphous (Cs) components of silk fibroin (SF). The role of these polypeptides in promoting the nucleation of hydroxyapatite (HA) has been previously investigated, yet is still not fully understood. Here we study the potential of HA mineralization via FDPs incorporated at 1:10, 1:2 and 1:1 in a plastically compressed (PC) and dense collagen (DC) scaffold. Scaffolds were immersed in simulated body fluid (SBF) at physiological conditions (pH = 7.4, 37°C) to promote biomineralization. The effect of Cs and Cp to promote HA nucleation was investigated at different time points, and compared to pure DC scaffolds. Characterization of Cs and Cp fragments using Liquid Chromatography-Mass Spectrometry (LCMS) showed little difference in the amino acid composition of the FDPs. Results obtained in vitro using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) X-Ray Diffraction (XRD) and mass analysis showed little difference between scaffolds that incorporated Cs, Cp, and DC hydrogels. These results demonstrated that silk FDPs incorporation are not yet suitable to promote HA nucleation in vivo without further refining the collagen-FDP system.
... Particularly, they represent significant steps towards induced mechanical enhancement of biological raw materials that will largely surpass previous (limited) attempts that used conventional chemical surface modification approaches. [42,43] Another example comes from a study that demonstrated that marine sponges can also biologically incorporate exogenous inorganic compounds (titanium water precursor) and use them to build skeletal elements with mixed silica-titania composition. High-resolution transmission electron microscopy (HR-TEM) and elemental analysis (elemental dispersive X-rays (EDX)) showed that titanium was biologically incorporated into these siliceous skeletal elements. ...
What is biological fabrication? It is combining the ability of designing bioinspired molecules (chemistry) with nature's complexity and ingenious paths (biology) in order to produce new composite materials with emergent properties while being able to tailor the said materials' end‐functionality or functionalities. And what is material farming? It is the possibility to implement alternative and sustainable methodologies of biological fabrication toward larger scales, real‐life applications, and marketable products. The proof‐of‐principle is recently demonstrated for biological fabrication of fibers with tailored properties using an in vitro cotton culture and designed glucose derivatives yielding fluorescent and supermagnetic cotton fibers. This new “fabrication approach” will allow, in the future, to sustainably transform abundant raw materials into an innovative new class of composite functional materials, such as a new generation of smart textiles in the above case of cotton. This essay provides a very brief overview of the research done in cotton, the methodology used for the biological fabrication of cotton fibers with tailored properties and, finally, showcases perspectives on the future of this new and exciting research field that challenges the present fabrication methodologies that heavily rely on an old mindset toward bio‐based fabrication strategies.
... Successful attempts to improve the mechanical properties of spider silk have been limited [34,40]. This is due to the difficulty of developing an adequate spinning methodology, balancing extrusion, drawing, yield and purity [41]. ...
... due to the CO 2 anaesthesia of spiders [45] and the consequent loss of active control of their silk spinning [46]. From a technological point of view, wet-spinning [47], electro-spinning [48], hand-drawing [42] or microfluidic approaches [49] have been investigated to produce an artificial silk at the laboratory scale, mechanically [34], structurally [40] or chemically [49] modified with respect to the natural one. However, a critical step is still needed to reach commercial-scale. ...
... It is light in weight, hence easy to carry [1]. A biodegradable material can be prepared based on silk fibroin and keratin present in spider silk [59,64].Spider silk suggested to be used as a load bearing biomaterial by Brown et al., (2011) due to its biocompatibility, strength and toughness. Spiders have a wide insect host range and thus can act as biological control agents of insect pests in agro-ecosystems (Jeyaparvathi et al., 2013). ...
