Wild silkworm cocoon as a natural tough biological composite structure

Silk cocoons are biological composites with intriguing characteristics that have evolved through a long natural selection process. Knowledge of structure-property-function relationship of multilayered composite silk cocoon shells gives insight into the design of next-generation protection materials. The current investigation studied the composite structure and mechanical performance of a wild silkworm cocoon (Chinese tussah silkworm cocoon, Antheraea pernyi) in comparison with the domestic counterpart (Mulberry silkworm cocoon, Bombyx mori). 180º peel and tensile tests were performed on the cocoon walls to understand both their interlaminar and in-plane mechanical properties. The fracture surfaces were investigated under SEM. The wild cocoon showed substantially higher toughness over the domestic cocoon, which explains their unique capability to tackle severe environmental adversaries.

Crystals in Antheraea assamensis silkworm cocoon: their removal, recovery and roles

Brick shaped mineral deposits or crystals are found in the shell of semi-domestic silk cocoon of Antheraea assamensis (A. assamensis). Effective removal and recovery of these crystals are important to understand their roles in the cocoon's protective function towards pupae. In this study, chemical and physical (ultrasonication) demineralisation methods were investigated for A. assamensis. It was found that the physical demineralisation method could effectively separate crystals without changing their shape and size and not effecting other components of the silk cocoon. The efficient recovery of the crystals, without any change in their chemical composition was confirmed based on FTIR, XRD and EDX techniques. Chemical demineralisation method was optimised and performed under milder conditions than reported in the past. It helped reeling of silk without much loss of strength or natural colour of silk fibre.

Inspirations from the protective silkworm cocoon structure

The main aim of this work is to understand the structureproperty-function relationship of the natural protective silkworm cocoon shells. This understanding will inspire further effort to tackle the perennial challenge of developing lightweight and highly protective textiles and composite structures. Such materials are essential for a wide range of applications including outdoor activities, healthcare, security, as well as defence sectors.

Directional moisture transfer through a wild silkworm cocoon wall

A silkworm cocoon is a porous biological structure with multiple protective functions. In the current work, the authors have used both experimental and numerical methods to reveal the unique moisture transfer characteristics through a wild Antheraea pernyi silkworm cocoon wall, in comparison with the long-domesticated Bombyx mori silkworm cocoon walls. The water vapor transmission and water vapor permeability (WVP) properties show that the A. pernyi cocoons exhibit directional moisture transfer behavior, with easier moisture transfer from inside out than outside in [e.g., the average WVP is 0.057 g/(h m bar) from inside out and is 0.034 g/(h m bar) from outside in]. Numerical analysis shows that the cubic mineral crystals in the outer section of the A. pernyi cocoon wall create a rough surface that facilitates air turbulence and promotes disturbance amplitude of the flow field, leading to lengthened water vapor transfer path and increased tortuosity of the moist air. It also indicates the vortex of water vapor can be generated in the outer section of cocoon wall, which increases the diffusion distance of water vapor and enhances the turbulence kinetic energy and turbulence eddy dissipation, signifying higher moisture resistance in the outer section. The difference in moisture resistance of the multiple A. pernyi cocoon layers is largely responsible for the unique directional moisture transfer behavior of this wild silkworm cocoon. These findings may inspire a biomimicry approach to develop novel lightweight moisture management materials and structures.

Heat and moisture transfer through silkworm cocoon walls.

A silkworm cocoon is a biological porous structure which provides multiple protective functions. The knowledge from this natural protective system could contribute to develop advanced materials and structures with superior performances and meet the human demanding of novel breathable materials for enhanced thermal protection and comfort.

Cocoon of the silkworm Antheraea pernyi as an example of a thermally insulating biological interface.

Biological materials are hierarchically organized complex composites, which embrace multiple practical functionalities. As an example, the wild silkworm cocoon provides multiple protective functions against environmental and physical hazards, promoting the survival chance of moth pupae that resides inside. In the present investigation, the microstructure and thermal property of the Chinese tussah silkworm (Antheraea pernyi) cocoon in both warm and cold environments under windy conditions have been studied by experimental and numerical methods. A new computational fluid dynamics model has been developed according to the original fibrous structure of the Antheraea pernyi cocoon to simulate the unique heat transfer process through the cocoon wall. The structure of the Antheraea pernyi cocoon wall can promote the disorderness of the interior air, which increases the wind resistance by stopping most of the air flowing into the cocoon. The Antheraea pernyi cocoon is wind-proof due to the mineral crystals deposited on the outer layer surface and its hierarchical structure with low porosity and high tortuosity. The research findings have important implications to enhancing the thermal function of biomimetic protective textiles and clothing.

Lessons from silkworm cocoons for future protective materials design

 Evolved over millions of years’ natural selection, very thin and lightweight wild silkworm cocoons can protect silkworms from environmental hazards and physical attacks from predators while supporting their metabolic activity. The knowledge of structure-property-function relationship of multi-layered composite silk cocoon shells gives insight into the design of next-generation protection materials. The mechanical and thermal insulation properties of both domestic (Bombyx mori, or B. moriand Samia. cynthia, or S. cynthia) and wild (Antheraea pernyi and Antheraea mylitta, or A. pernyi and A. mylitta) silkworm cocoons were investigated. The research findings are of relevance to the bio-inspired design of new protective materials and structures.
The 180 degree peel tests and needle penetration tests were used for examining the peel resistance and needle penetration resistance of both domestic and wild silkworm cocoon walls. The temperatures inside and outside of the whole silkworm cocoons under warm, cold and windy conditions were monitored for investigating the cocoon’s thermal insulation function. Computational fluid dynamics (CFD) models were created to simulate the heat transfer through the A. pernyi cocoon wall.
The wild cocoons experienced much higher peeling peak loads than the domestic cocoon. This transfers to a maximum work-of-fracture (WOF) of about 1000 J/m2 from the A. pernyi outer layer, which was 10 times of the B. mori cocoon. The A. pernyi wild cocoon exhibited a maximum penetration force (11 N) that is 70 % higher than a woven aramid fabric. Silk sericin is shown to play a critical role in providing needle penetration resistance of the non-woven composite cocoon structure by restricting the relative motion of fibres, which prevents the sharp tip of the needle from pushing aside fibres and penetrating between them. The wild A. pernyi cocoon exhibits superior thermal buffer over the domestic B. mori cocoon. The unique structure of the A. pernyi cocoon wall with mineral crystals deposited on the cocoon outer surface, can prohibit most of the air from flowing inside of the cocoon structure, which shows strong wind resistance under windy conditions.

Microstructure and mechanical properties of silk from different components of the Antheraea pernyi cocoon

Silk fibres from different components of the Antheraea pernyi silkworm cocoon, namely peduncle, outer floss, and cocoon shells (outermost layer and pelade layer) were studied in detail to gain insights into the structure-property-function relationship. Among the fibres from different components, peduncle fibres are the softest with the largest viscoelastic lag, which may reduce the oscillation amplitude when a cocoon hangs on a twig. Fibres from the outermost layer are the toughest and have the largest breaking energy. Outer floss fibres have the highest content of sericin (about 11.98%) but their hardness and elasticity are intermediate. Pelade fibres are shape - preservable and stable with superior hardness and elasticity. The understanding of the properties of different silk fibres is essential for understanding their respective roles in the function of a silk cocoon and will also inspire new designs of protective materials under stringent environmental conditions.

The effect of fibrous structural difference on thermal insulation properties of biological composites: silkworm cocoons

As a biological fibrous structure, silkworm cocoon provides multiple protective functionalities to safeguard the silk moth pupa’s metabolic activity. The mechanism of this protection could be adopted in clothing manufacture to provide more comfortable apparel. In this study, the thermal insulation properties of both domestic Bombyx mori (B. mori) and wild Antheraea pernyi (A. pernyi) cocoons were investigated under both warm and cold environmental conditions. Computational fluid dynamics models have been developed to simulate the heat transfer process through both types of cocoon wall structures. The simulation results show that the wild A. pernyi cocoon reduces the intensity of convection and heat flux between the environment and the cocoon interior and has higher wind resistance than its domestic counterpart. Compared with A. pernyi cocoon, the B. mori cocoon facilitates easy air transfer and decreases the temperature lag when the surrounding conditions are changed. The new knowledge has significant implications for developing biomimetic thermal functional materials.

Fabrication of a corneal-limbal tissue substitute using silk fibroin

Fibroin extracted from silkworm cocoon silk provides an intriguing and potentially important biomaterial for corneal reconstruction. In the present chapter we outline our methods for producing a composite of two fibroin-based materials that supports the co-cultivation of human limbal epithelial (HLE) cells and human limbal stromal (HLS) cells. The resulting tissue substitute consists of a stratified epithelium overlying a three-dimensional arrangement of extracellular matrix components (principally ‘degummed’ fibroin fibers) and mesenchymal stromal cells. This tissue substitute is currently being evaluated as a tool for reconstructing the corneal limbus and corneal epithelium.

Análises técnica e energética da secagem combinada no processamento de casulo do bicho-da-seda de Bombyx Mori L

Pós-graduação em Agronomia (Energia na Agricultura) - FCA