173,911 research outputs found
Flaw-tolerance in silk fibrils explains strength, extensibility and toughness of spider silk
No full textSilk is an ancient but remarkably strong, extensible and tough material made from simple protein building blocks. Earlier work has shown that the particular molecular geometry of silk with a composite of semi-amorphous and nanocrystalline beta-sheet protein domains provides the structural basis for its characteristic softening-stiffening behavior and remarkable strength at the nanoscale. Yet, an open question remains as to how these nanoscale properties are upscaled so effectively to create strong, extensible and tough silk fibers. Here we discover that the geometric confinement of fibrils to ≈50-100 nm width and arranged in bundles to form larger-scale silk fibers, is the key to explaining the upscaling of the mechanical properties of silk from the atomistic scale upwards. We find that under this geometric confinement, hundreds of thousands of protein domains unfold simultaneously and thereby act synergistically to resist deformation and failure, providing access to enhanced large-scale strength, extensibility and toughness. Moreover, since the material is in a flaw-tolerant state under this geometric confinement, structural inhomogeneities such as cavities or tears that typically act as stress concentrators do not compromise the material performance. Indeed, experimental work showed that the diameter of silk fibrils that make up larger-scale silk fibers are on the order of 20-100 nm, in agreement with our findings. The exploitation of this mechanism in engineering design enables the synthesis of hierarchical fiber materials for superior performance despite limited and inferior building blocks
Molecular and nanostructural mechanisms of deformation, strength and toughness of spider silk fibrils
No full textSpider silk is one of the strongest, most extensible and toughest biological materials known, exceeding the properties of many engineered materials including steel. Silks feature a hierarchical architecture where highly organized, densely H-bonded beta-sheet nanocrystals are arranged within a semi-amorphous protein matrix consisting of 31-helices and beta-turn protein structures. By using a bottom-up molecular-based mesoscale model that bridges the scales from Angstroms to hundreds of nanometers, here we show that the specific combination of a crystalline phase and a semi-amorphous matrix is crucial for the unique properties of silks. Specifically, our results reveal that the superior mechanical properties of spider silk can be explained solely by structural effects, where the geometric confinement of beta-sheet nanocrystals combined with highly extensible semi-amorphous domains with a large hidden length is the key to reach great strength and great toughness, despite the dominance of mechanically inferior chemical interactions such as H-bonding. Our model directly shows that semi-amorphous regions unravel first when silk is being stretched, leading to the large extensibility of silk. Conversely, the large-deformation mechanical properties and ultimate tensile strength of silk is controlled by the strength of beta-sheet nanocrystals, which is directly related to their size, where small beta-sheet nanocrystals are crucial to reach outstanding levels of strength and toughness. Our model agrees well with observations in recent experiments, where it was shown that a significant change in the strength and toughness can be achieved solely by tuning the size of beta-sheet nanocrystals. Our findings unveil the material design strategy that enables silks to achieve superior material performance despite simple and inferior constituents, resulting in a new paradigm in materials design where enhanced functionality is not achieved using complex building blocks, but rather through the utilization of simple repetitive constitutive elements arranged in hierarchical structures
Evidence of the Most Stretchable Egg Sac Silk Stalk, of the European Spider of the Year Meta menardi
No full textSpider silks display generally strong mechanical properties, even if differences between species and within the same species can be observed. While many different types of silks have been tested, the mechanical properties of stalks of silk taken from the egg sac of the cave spider Meta menardi have not yet been analyzed. Meta menardi has recently been chosen as the “European spider of the year 2012”, from the European Society of Arachnology. Here we report a study where silk stalks were collected directly from several caves in the north-west of Italy. Field emission scanning electron microscope (FESEM) images showed that stalks are made up of a large number of threads, each of them with diameter of 6.03±0.58 µm. The stalks were strained at the constant rate of 2 mm/min, using a tensile testing machine. The observed maximum stress, strain and toughness modulus, defined as the area under the stress-strain curve, are 0.64 GPa, 751% and 130.7 MJ/m[superscript 3], respectively. To the best of our knowledge, such an observed huge elongation has never been reported for egg sac silk stalks and suggests a huge unrolling microscopic mechanism of the macroscopic stalk that, as a continuation of the protective egg sac, is expected to be composed by fibres very densely and randomly packed. The Weibull statistics was used to analyze the results from mechanical testing, and an average value of Weibull modulus (m) is deduced to be in the range of 1.5–1.8 with a Weibull scale parameter (σ[subscript 0]) in the range of 0.33–0.41 GPa, showing a high coefficient of correlation (R[superscript 2] = 0.97).Presidential Early Career Award for Scientists and Engineers (award number N00014-10-1-0562
Surveying silk fibre degradation by crystallinity determination: a study on the Tang-Dynasty silk treasure from Famen Temple, China
No full textWhen Chinese archaeologists opened an unknown vault under the collapsed pagoda of Famen Temple near Xian (Shaanxi Province, NW China) in 1987, they found a vast amount of valuable silk textiles. The degraded textiles were part of a treasure comprising hundreds of artifacts deposited by Tang dynasty (ad 618–907) emperors as a gift to the temple. Run as a bilateral German-Chinese project, the Roemisch-Germanisches Zentralmuseum Mainz established a textile conservation laboratory in Shaanxi´s provincial capital Xian in 2001, joining numerous other laboratories that have existed there since the early 1990s.This preliminary study represents part of an ongoing investigation programme that accompanies the conservation work. The Tang dynasty silk is generally in a very poor state of preservation as a result of its long burial period. Large sections have only survived as an amorphous brown mass of fibre debris. Some parts are better preserved, however, offering the unique opportunity to study the whole range of degradation stages on ancient silks.This preliminary scientific investigation focuses on the determination of the silk fibres’ crystallinity and its relation to the ageing process. As we know from modern material, silk is mainly crystalline, albeit in a somewhat amorphous state. The methods of investigation used were X-ray diffraction (XRD) using synchrotron radiation, which is a new way to determine crystallinity of ancient silk fibres; and polarized Fourier transform infrared spectroscopy (FTIR) for the determination of crystallite orientation. Both methods were specifically devised to gain information on small single fibres
New Evidence for Early Silk in the Indus Civilization
No full textSilk is an important economic fiber, and is generally considered to have been the exclusive cultural heritage of China. Silk weaving is evident from the Shang period, though the earliest evidence for silk textiles in ancient China dates to more than a millennium earlier. New study of fibers from Harappan bronze artifacts reveals surprising early evidence for knowledge of silkworking in South Asia, the earliest evidence in the world for any silk outside China, and roughly contemporaneous with the earliest Chinese evidence for silk. This important new finding brings into question the traditional historical notion of sericulture as being an exclusively Chinese invention
Productivity Improvement in the Specialized Industrial Clusters: The Case of the Japanese Silk-Reeling Industry
No full textWe examine two sources of productivity improvement in the specialized industrial clusters. Agglomeration improves the productivity of each plant through positive externalities, shifting plant-level productivity distribution to the right. Selection expels less productive plants through competition, truncating distribution on the left. By analyzing the data of the early twentieth century Japanese silk-reeling industry, we find no evidence confirming a right shift in the distribution in clusters or that agglomeration promotes faster productivity growth. These findings imply that the plant-selection effect was the source of higher productivity in the Japanese silk-reeling clusters.Economic geography, Heterogeneous firms, Selection, Productivity
Gravitational microlensing by clustered machos
No full textIt has been proposed that the MACHOs in our Galaxy could be clumped in globular cluster-like associations or RAMBOs (robust associations of massive baryonic objects) (Moore & Silk). Here we investigate the effect such clustering has on the microlensing of stars in the Large Magellanic Cloud. We find that the lensing in a 1 square degree field could be dominated by just a few clusters. As a result the lensing properties vary widely depending on the position and velocity of those clusters which happen to lie between us and the LMC. Moreover, we find a large variance in timescale distributions that suggests that the small-number statistics could easily be dominated by events in the tails of the unclustered distribution (e.g., by long periods). We compare our results with the MACHO collaboration data and find that a "standard" halo made entirely of MACHOs is not strongly disfavored if the clusters have masses of 106 M. For less massive clusters such a halo is not as likely. For 104 M clusters the microlensing statistics are essentially unchanged from the unclustered case. It may be possible to detect very massive clusters from the distribution of events in timescale and space. We provide some examples of timescale distributions. © 1996. The American Astronomical Society. All rights reserved
Agglomeration or Selection? The Case of the Japanese Silk-Reeling Clusters, 1908-1915
No full textWe examine two sources of productivity improvement in the specialized industrial clusters of the early twentieth century Japanese silk-reeling industry. Agglomeration improves the productivity of each plant through positive externalities, shifting plant-level productivity distribution to the right. Selection expels less productive plants through competition, truncating distribution on the left. We find no evidence confirming a right shift in the distribution in clusters or that agglomeration promotes faster productivity growth. Rather, the distribution in clusters was severely left truncated, even for younger plants. These findings imply that the plant-selection effect was the source of higher productivity in the Japanese silk-reeling clusters.Economic geography, Heterogenous firms, Industrial clusters, Productivity
Skin grafts : local quest for viable alternatives to autologous grafts using silk and acellular dermal matrices
No full textThe gold standard with regards to skin transplantation is the use of the patient’s own skin obtained from a healthy donor site. Such grafts can be either full thickness skin or more commonly nowadays, split thickness skin. Various materials, having either natural and or synthetic origins, have been used in the engineering of skin substitutes to-date and these grafts are then confronted against autologous skin grafts. If proven to be successful, such matrices could be utilised in clinical applications such as in the treatment of burn wounds and in cases of skin ulcers amongst others.
In this study the primary cells used, keratinocytes and fibroblast, were obtained from donor skin and cultured. Scaffolds of xenogenic (raw silk) as well as of allogenic (acellular dermal matrices) origins were obtained via low-cost methods and seeded using the fibroblasts and keratinocytes so as to determine which gave the closest mimic to skin grafts.
Out of the matrices assessed, the raw silk matrix allowed the best colonisation with skin cells in our hands. The ADM matrice also showed some cell colonisation, but will need further experimentation.peer-reviewe
Silk, J J, 405092
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/416841Surname: SILK. Given Name(s) or Initials: J J. Military Service Number or Last Known Location: 405092. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 13689.239182
Item: [2016.0049.49102] "Silk, J J, 405092
- …
