Spider silk, particularly the dragline silk used for the framework of a web, is a biopolymer with extraordinary characteristics. This material combines incredible tensile strength—often compared favorably to steel by weight—with remarkable elasticity and toughness. This unique blend makes dragline silk highly desirable for applications in medicine, textiles, and advanced materials science. The core challenge is that this superior material is produced only by spiders in tiny quantities. Obtaining a steady, large-scale supply of the protein building blocks, known as spidroins, has been the primary obstacle to commercializing spider silk products.
Why Traditional Spider Farming Fails
Attempts to harvest spider silk commercially by farming spiders have proven to be an economic and logistical failure. Unlike the communal silkworms, most spider species are highly territorial and solitary.
Spiders are cannibalistic; if housed in close proximity, they will kill and eat one another, making dense, efficient farming impossible. Raising the animals in individual habitats requires immense space, labor, and resources, quickly making the operation financially impractical.
The second major limitation is the extremely low yield of silk from a single spider. Even the largest orb-weavers produce only minute amounts of dragline silk at a time. To produce a single pound of raw silk thread would necessitate collecting silk from hundreds of thousands to over a million individual spiders, a scale that is not feasible for industrial production.
Mechanical Milking for Research Purposes
Researchers still require natural silk to study its molecular structure and mechanical performance, despite the inability to farm spiders for mass production. To acquire pristine, long strands of silk for analysis, scientists use a laborious technique often called “forced silking” or mechanical milking. This process is strictly for laboratory-scale study and is not a viable commercial harvesting method.
The procedure begins by gently securing the spider, often after a brief period of sedation, to a fixed surface to immobilize it. A researcher then carefully locates the tiny silk-producing spinnerets on the spider’s abdomen. The fine silk thread is manually attached to a motorized spool or rotating wheel.
The wheel is then slowly accelerated to draw the silk out from the major ampullate gland, mimicking the natural reeling process. This technique can yield several hundred feet of continuous fiber from a single spider, but it is time-consuming and must be repeated every few weeks, yielding only microgram quantities. The resulting samples are invaluable for testing the silk’s properties, such as tensile strength and elasticity.
Bioengineered Production of Spider Silk Proteins
The modern, scalable solution to the harvesting problem involves bypassing the spider entirely through genetic engineering. Scientists isolate the genes responsible for producing the silk proteins, known as spidroins, and insert them into host organisms that are easier and more economical to cultivate. The primary proteins targeted are Major Ampullate Spidroins 1 and 2 (MaSp1 and MaSp2), which give dragline silk its signature strength and toughness.
Various host systems have been successfully used to express these proteins. These include bacteria like E. coli and yeast, which are grown in large bioreactors to produce significant quantities of the recombinant protein. Other approaches involve using transgenic animals, such as silkworms or goats engineered to secrete spidroins in their milk. Protein purification is a crucial step, isolating the spidroins from the host organism’s other cellular components.
Once the spidroin protein is purified, the final and most complex step is “wet-spinning” the solution into a usable fiber, a process that mimics the natural silk gland. The purified protein is dissolved to create a viscous solution and then forced through a micro-spinneret into a coagulation bath, often containing an alcohol or a specific salt solution.
This chemical environment and the shear force applied during extrusion cause the dissolved spidroin molecules to rapidly align and solidify, forming a continuous fiber. This biomimetic approach is necessary because the mechanical properties of the final silk depend highly on replicating the precise conditions that occur inside the spider’s spinning duct.