Spider Silk
Preamble
- Every spider can produce six diverse types of silk from six different silk glands: Golden Orb Weaver spiders (Nephila edulis) is one of them.
- It belongs to Phylum Arthropoda and Class Arachnida.
- This species is fascinating due to its ability to produce yellow-coloured silk, making it potentially valuable for textile and other purposes.
- Spider silk is one of its kind as it is finer than silk but possesses strength like steel as it belongs to a type of bio-elastic fibre .
- It is highly resilient and durable, tough, and elastic, bio-degradable, and eco-friendly, has a lustrous appearance and is soft to the touch.
- It can withstand significant impact forces without being damaged and its static load and impact resistance is better than other natural and artificial materials .
- Spider silk tends to shrink when in contact with water; thus, properties will tend to change.
Milking Process, the Spinnerets, and the Dragline Silk
- Using this delicate milking process, they can harvest up to 700 meters of silk in one continuous strand .
- The silk that can be produced for textile purposes is mainly dragline silk from the spider’s major ampullate gland, used to make the outer scaffolding of a web, and minor ampullate silk, used to create the finer spiral in the web.
- The spider consists of organs known as spinnerets in the abdomen.
- The web creation is initiated by the spider secreting a proteinaceous liquid from finger-like projections on the spinnerets.
- As this liquid comes in contact with the outer atmosphere, it dries, forming a thread-like structure.
- While each spinneret releases the liquid, the strands produced are twisted, simultaneously making them stronger.
- Dragline silk is mainly possessing exceptional mechanical properties such as high tensile strength and extensibility, toughness, and elasticity.
- It is as light as a feather and finer than a human hair.
Table 1. Physical & mechanical properties and chemical composition of areca nut fibres
Physical and Mechanical properties
Tensile strength
5×109 N/m2
Elongation at break
35-50%
Breaking energy
1×105 J/kg
Chemical composition
The main components are Glycine, Alanine, and a small amount of Serine.
Typical uses
- Scientists have attempted to use this unique fibre by making bulletproof armour, violin strings, medical bandages, optical fibre cables, etc.
- In 2012, a cape made from silk obtained from 1.2 million Golden Orb spiders from Madagascar was displayed at the V&A in London.
- It took 8 years to create this magnificent cape, as milking spiders and collecting sufficient silk for significant projects can be intricate and time-consuming.
- Ancient Greeks used it to stop bleeding and heal wounds, whereas the Indigenous people used it as a fishing line.
- By World War II, Spider silk was used in optical device of the sighting system of telescope, gun, etc .
- It has good biocompatibility and biodegradability, which makes it an ideal option for medical applications. E.g., artificial tendons and ligaments, surgical sutures, etc.
Table2.Schematic overview of different silk types produced by female orb-weaving spiders (Araneae). Each silk type (highlighted in red) is tailored for a specific purpose.
Silk producing glands
Aggregate
Pyriform
Tubuliform
Flagelliform
Aciniform
Minor Ampullate
Major Ampullate
Types of spider silk
Aqueous cement
Core fibre of capture spiral
Egg-case silk
Capture silk
Dragline silk
Framework silk
Dragline silk
Framework silk
Radial silk
Chart 1: Types of silk secreted by a spider through different glands
