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a One half of the cocoon (horizontal cut, average length 5.0 cm) showing the inner (smooth) and the outer (coarse) surface morphology. b SEM image: the outer surface of the cocoon exhibiting the rough morphology. The particulate covering the surface of the silk fibers. c A high resolution SEM image of the outer surface of the cocoon showing the uneven texture due to the presence of crystals of different sizes. d At higher resolution SEM image cuboidal shaped crystals were irregularly stacked over one another. Dimension of the cuboidal crystals: the crystals were of approximately 1-2 l in length and 1-2 l in breadth. e The SEM image of the inner surface of the cocoon exhibits a smooth texture with intertwined silk fibers crisscross' the surface. f It shows the inner surface between the fibers with irregular gaps with few particulates. There were very few 

a One half of the cocoon (horizontal cut, average length 5.0 cm) showing the inner (smooth) and the outer (coarse) surface morphology. b SEM image: the outer surface of the cocoon exhibiting the rough morphology. The particulate covering the surface of the silk fibers. c A high resolution SEM image of the outer surface of the cocoon showing the uneven texture due to the presence of crystals of different sizes. d At higher resolution SEM image cuboidal shaped crystals were irregularly stacked over one another. Dimension of the cuboidal crystals: the crystals were of approximately 1-2 l in length and 1-2 l in breadth. e The SEM image of the inner surface of the cocoon exhibits a smooth texture with intertwined silk fibers crisscross' the surface. f It shows the inner surface between the fibers with irregular gaps with few particulates. There were very few 

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Silk is the generic name given to the fibrous proteins spun by a number of arthropods. During metamorphosis, the larva of the silk producing arthropods excrete silk-fiber from its mouth and spun it around the body to form a protective structure called cocoon. An adult moth emerges out from the cocoon after the dormant phase (pupal phase) varying fr...

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... visual observation, the outer surface of the cocoon exhibited extremely rough morphology as compared to the inner surface (Fig. ...
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... SEM analysis, we found the presence of large number of cuboidal shaped crystals on the outer surface of silk fibers ( Fig. 3b-d). These varied size crystals were randomly stacked over one another like tiles covering the silk thread and later identified as the crystals of calcium oxalate monohydrate by XRD and FTIR studies. In contrast, the inner surface of the cocoon was found to be extremely smooth ( Fig. 3 a) with intertwined cross-network of the fibers (Fig. 3e, f). Hardly any crystals were observed on the inner surface of the ...
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... SEM analysis, we found the presence of large number of cuboidal shaped crystals on the outer surface of silk fibers ( Fig. 3b-d). These varied size crystals were randomly stacked over one another like tiles covering the silk thread and later identified as the crystals of calcium oxalate monohydrate by XRD and FTIR studies. In contrast, the inner surface of the cocoon was found to be extremely smooth ( Fig. 3 a) with intertwined cross-network of the fibers (Fig. 3e, f). Hardly any crystals were observed on the inner surface of the ...
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... SEM analysis, we found the presence of large number of cuboidal shaped crystals on the outer surface of silk fibers ( Fig. 3b-d). These varied size crystals were randomly stacked over one another like tiles covering the silk thread and later identified as the crystals of calcium oxalate monohydrate by XRD and FTIR studies. In contrast, the inner surface of the cocoon was found to be extremely smooth ( Fig. 3 a) with intertwined cross-network of the fibers (Fig. 3e, f). Hardly any crystals were observed on the inner surface of the ...
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... the Calcium Oxalate Monohydrate Layer from the Outer Surface Figure 3g, h showed the SEM images of the outer surface of the treated cocoons. On comparison with the outer sur- face of the untreated cocoons, it is clearly demonstrated Fig. 2 a Schematic experimental set-up to study the diffusion of CO 2 from inside to outside the cocoon: The dead pupa was removed from the cocoon by making a narrow cut at the top of the cocoon and this cut was sealed by wrapping with a narrow band of para-film keeping the surface intact. A narrow glass tube was inserted on the top of the cocoon to supply CO 2 gas. The cocoon was allowed to hang in an air-tight beaker container containing Ca(OH) 2 solution. CO 2 was generated as shown in the figure using CaCO 3 and dilute HCl solution. As soon as CO 2 gas was allowed to pass inside the cocoon through the glass tube, the CO 2 started diffusing out of the cocoon. We recorded the time as soon as we observed the appearance of milky white smear on the Ca(OH) 2 solution. b Schematic experimental set-up to study the diffusion of CO 2 from outside to inside the cocoon: the dead pupa was removed from the cocoon and the cut was sealed by para-film. A narrow glass tube was inserted into the cocoon and the other end of the tube was immersed in Ca(OH) 2 solution in a beaker which was maintained under the blanket of argon flow to prevent contamination from aerial carbon dioxide. The cocoon was hung in an air tight beaker having an inlet for the passage of CO 2 with a narrow hole at a distance for free gas passage. Sometimes we blocked this narrow passage to generate CO 2 pressure on the outer surface of the cocoon. The generated CO 2 gas was allowed to pass for more than 10 min. We performed this experiment on 11 different cocoons (n = 11) and in each case the Ca(OH) 2 solution remained unaffected. c Schematic experimental set-up to study the diffusion of O 2 from inside to outside the cocoon: the experimental set-up was similar to the CO 2 detection setup. Except O 2 detection was done by using sodium pyrogallate as an absorbent. On absorbing O 2 , the color of the sodium pyrogallate solution changes to dark brown. This experiment needed an extremely inert environment. Inert environment was created by purging the set-up with excess argon gas. When under argon purging the pyrogallol solution remained pale yellow, the valve of the oxygen cylinder was opened very gently and within minutes the indicator solution turned deep-brown showing the diffusion of O 2 from inside to outside of the cocoon membrane. The experiment was repeated with 10 different cocoons showing the same result. d Schematic experimental set-up to study the diffusion of O 2 from outside to inside the cocoon: the preparation of empty cocoon was done as described earlier. The alkaline pyrogallol solution was placed under constant argon purging to avoid interaction with air. The set up was first purged with argon for 30 min and then a flow of oxygen gas was introduced. Within minutes the pale yellow pyrogallol solution turned deep brown. The experiment was repeated with 10 different cocoons showing the same result that the calcium oxalate monohydrate layer has completely leached away from the outer surface of the cocoon. As expected, there is hardly any noticeable change in the inner surface of the treated cocoon compared to that with the untreated cocoons (Fig. ...
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... the Calcium Oxalate Monohydrate Layer from the Outer Surface Figure 3g, h showed the SEM images of the outer surface of the treated cocoons. On comparison with the outer sur- face of the untreated cocoons, it is clearly demonstrated Fig. 2 a Schematic experimental set-up to study the diffusion of CO 2 from inside to outside the cocoon: The dead pupa was removed from the cocoon by making a narrow cut at the top of the cocoon and this cut was sealed by wrapping with a narrow band of para-film keeping the surface intact. A narrow glass tube was inserted on the top of the cocoon to supply CO 2 gas. The cocoon was allowed to hang in an air-tight beaker container containing Ca(OH) 2 solution. CO 2 was generated as shown in the figure using CaCO 3 and dilute HCl solution. As soon as CO 2 gas was allowed to pass inside the cocoon through the glass tube, the CO 2 started diffusing out of the cocoon. We recorded the time as soon as we observed the appearance of milky white smear on the Ca(OH) 2 solution. b Schematic experimental set-up to study the diffusion of CO 2 from outside to inside the cocoon: the dead pupa was removed from the cocoon and the cut was sealed by para-film. A narrow glass tube was inserted into the cocoon and the other end of the tube was immersed in Ca(OH) 2 solution in a beaker which was maintained under the blanket of argon flow to prevent contamination from aerial carbon dioxide. The cocoon was hung in an air tight beaker having an inlet for the passage of CO 2 with a narrow hole at a distance for free gas passage. Sometimes we blocked this narrow passage to generate CO 2 pressure on the outer surface of the cocoon. The generated CO 2 gas was allowed to pass for more than 10 min. We performed this experiment on 11 different cocoons (n = 11) and in each case the Ca(OH) 2 solution remained unaffected. c Schematic experimental set-up to study the diffusion of O 2 from inside to outside the cocoon: the experimental set-up was similar to the CO 2 detection setup. Except O 2 detection was done by using sodium pyrogallate as an absorbent. On absorbing O 2 , the color of the sodium pyrogallate solution changes to dark brown. This experiment needed an extremely inert environment. Inert environment was created by purging the set-up with excess argon gas. When under argon purging the pyrogallol solution remained pale yellow, the valve of the oxygen cylinder was opened very gently and within minutes the indicator solution turned deep-brown showing the diffusion of O 2 from inside to outside of the cocoon membrane. The experiment was repeated with 10 different cocoons showing the same result. d Schematic experimental set-up to study the diffusion of O 2 from outside to inside the cocoon: the preparation of empty cocoon was done as described earlier. The alkaline pyrogallol solution was placed under constant argon purging to avoid interaction with air. The set up was first purged with argon for 30 min and then a flow of oxygen gas was introduced. Within minutes the pale yellow pyrogallol solution turned deep brown. The experiment was repeated with 10 different cocoons showing the same result that the calcium oxalate monohydrate layer has completely leached away from the outer surface of the cocoon. As expected, there is hardly any noticeable change in the inner surface of the treated cocoon compared to that with the untreated cocoons (Fig. ...

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... CaOx in the cocoon is regarded as detrimental to commercial exploitation since it makes reeling difficult. In the cocoon, CaOx performs a variety of functions, including defence, water resistance, CO2 gating, reflection, thermal insulation, etc. (Roy et al. 2012;Zhang et al. 2013). It's still a mystery which genes are triggered to accumulate calcium deposits in the cocoon and how skillfully silkworms have utilized the minor constituent for their cocoon construction. ...
... In a comparative study between A. mylitta and Bombyx mori, calcium content was reported as high in (A) mylitta, whereas in (B) mori it was in trace amounts (Tulachan et al. 2014). Cuboidal crystals ranging from 1 to 2 μm are found in A. myllita (Roy et al. 2012). In A. assamensis, brick-shaped crystals are found (Kaur et al. 2015;Konno et al. 2014 have proved the synergistic plant defence role of raphide (CaOx) and cystine protease through the needle effect, whereas CaOx alone does not exhibit any defensive role. ...
... During spinning, wild silk moths pause to excrete crystal fluid, which aids in water resistance and avoids parasitoid penetration. In Antheraea pyrolei (tasar silkworm), the deposition of CaOx monohydrate in their cocoons may be attributed to the precipitation of oxalic acid in the Terminalia host plant (Roy et al. 2012). In Antheraea species, the CaOx irritates the invading predators. ...
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... Among them, passive and active ones can be differentiated. Passive properties are characterized by the lack of regulation since they continuously work to control and maintain the biological conditions that silkworm survival requires (e.g., mechanical properties, water and light protection, thermal regulation, [11,62] gas selective permeability, [63] antibacterial [64] and UV-protection, [65,66] among others). [67] Active properties allow monitoring and regulate the metamorphosis, linking the cocoon and pupa with the environment. ...
... This ability, result from cocoons composition, silk weave, and shape. [63,74,[76][77][78] Calcium oxalate hydrate crystals, found in some cocoon's composition, have a particular function in this process. However, due to different environmental conditions and even to the human-induced selection processes, the Bombyx mori lacks these crystals. ...
... However, due to different environmental conditions and even to the human-induced selection processes, the Bombyx mori lacks these crystals. [63,77] Despite this issue, some studies point out the applicability of Bombyx mori silk as a gas barrier, and the possibility to regulate gas permeation through β-sheets content (Figure 3c). [74] In particular, O 2 , CO 2 , and N 2 gases' ability to be permeated through SF decrease as β-sheets content increases. ...
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... These crystals, identified as calcium oxalates [14], are deposited on the outer and middle layer surface of the outer layer fiber [6]. This feature may have a functional role, such as preferential gating of CO 2 from the cocoon inside to outside and temperature regulation to maintain a physiological temperature inside the cocoon irrespective of the surrounding environment [30]. These varied size crystals are piled up on the silk fibers, especially in the crevices where fibers cross, and filling the gaps between them, thereby decreasing the cocoon porosity, as shown in Figures 6b and 7b. ...
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... Two peaks assigned to calcium oxalate appear in the activated samples. These peaks correspond to one vibration at 1624 cm −1 for the asymmetric (CO) and one vibration at 1320 cm −1 for the symmetric (CO) of the oxalate group [34]. The surface area and porosity of the AlBe-G samples are presented in Table 2. ...
... Two peaks assigned to calcium oxalate appear in the activated samples. These peaks correspond to one vibration at 1624 cm −1 for the asymmetric v a (CO) and one vibration at 1320 cm −1 for the symmetric v s (CO) of the oxalate group [34]. ...
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... Therefore, most of the silk weaving plants treat silk reeling wastewater as waste material. In rec ent years, it is believed that sericin has important biological characteristics, such as corrosion resistance, antibacterial activity, and ultraviolet radiation (UV) protection [24][25][26][27]. Sericin contains a large amount of serine and a high proportion of several polar amino acids, making it highly hydrophobic and adhesive and easy to absorb and release moisture content. ...
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Through biogenetic engineering, the posterior silk glands of Bombyx mori larvae are degenerated, and only the middle silk glands are retained to secrete sericin to produce sericin fibers, so as to obtain sericin cocoons with high sericin content (>98.5%). For this paper, sericin cocoons were studied, and the morphological structure characteristics and properties of sericin cocoons and common Bombyx mori cocoons were compared and analyzed through such modern test techniques as SEM, FTIR, and XRD. Results show that sericin cocoons have the basic morphological structure of cocoons, but because of the brittleness and hardness of sericin, the ssericin cocoons have poor integrity with a thermal decomposition rate that is higher than that of cocoons; the two cocoons are of a similar protein structure, with both α-helix and β-sheet structures, and dominantly the β-sheet structure; and the crystallinity of sericin cocoons (10.48%) is lower than that of the common Bombyx mori cocoons (27.10%). Sericin was extracted from both cocoons to obtain a mixed sericin solution respectively, which were coated on base fabrics of polyester taffeta (210T) for coating finish and subjected to qualitative research for their anti-UV properties. The base fabrics coated with mixed sericin solutions of sericin cocoons and Bombyx mori cocoons have an anti-UV performance index (UPF) of 23.9% and 22.5% respectively, which are higher than that of the base fabric (8.9%).