Is spider silk really stronger than steel?

Scientific Concepts, Discoveries, and Nature Phenomena

Spider silk composition and types

• Spider webs are made from multiple silk types, not one:
  • Dragline silk (major ampullate silk): forms the main structural “framework” / supporting strands.
  • Other silks serve roles such as anchoring, creating stretchy capture spirals, and sticky prey capture.
• A web can contain seven different silk types.
• Dragline (major ampullate) silk is the one most commonly compared to steel.

Mechanical testing concepts (how strength/toughness are quantified)

• Stress: force divided by cross-sectional area.
• Strain: relative stretching (change in length divided by original length).
• Ultimate tensile strength: maximum stress the material withstands before breaking.
• Toughness: proportional to the area under the stress–strain curve (energy absorbed before failure).

Key comparative measurements (steel, Kevlar, spider silk)

• “Typical” dragline silk sample: roughly ~600 MPa ultimate tensile strength.
• Darwin’s bark spider dragline silk: ~1,600 MPa (more than twice the sample).
• Experimental ultra-high strength steels: near ~3,000 MPa.
• Specific strength (strength relative to density):
  • Because steel is ~6× denser, spider silk can be about ~2× stronger by specific strength (“ounce for ounce,” same mass and length).

Toughness comparisons (energy absorption)

• Kevlar: up to ~50 MJ/m³ toughness.
• Experimental ultra-high strength steel: around ~170 MJ/m³ toughness.
• Spider silk: around ~205 MJ/m³ for one sample, and up to a peak ~520 MJ/m³ for Darwin’s bark spider dragline silk.
• Explanation given:
  • Kevlar tends to be stiffer (steeper rise in the stress–strain curve) and fails sooner, so it absorbs less total energy.
  • Spider silk is more extensible, enabling higher toughness.

Why spider silk is strong and tough (microstructure/material design)

• Spider silk proteins called spidroins self-organize into:
  • Nanocrystals / ordered regions: protein segments arranged like “stacked egg trays,” aligned along the fiber length.
  • Amorphous regions / less-ordered segments: more flexible regions that can deform and extend.
• Model described:
  • Rigid blocks (nanocrystals) connected by elastic cords (amorphous regions),
  • Producing both:
    • high resistance to pull-out/rupture (strength)
    • high energy absorption (toughness)

Biological processing: how spiders assemble silk inside glands

• Silk protein production starts in the spider tail (silk gland):
  • Spidroins have three main parts:
    • N-terminal
    • C-terminal
    • Repeating amino acid region
• Spidroins undergo changing conditions through the gland and spinning duct:
  • Tail / storage sac: high concentration; controlled by salt balance and pH so proteins repel instead of clumping.
  • Spinning duct: mechanical deformation (shear forces and stretching) plus chemical pH shift.
• Nanocrystal formation:
  • Some amino-acid sequences fold into ordered structures stabilized by hydrogen bonding, creating strong crystalline regions.
• Amorphous stretch:
  • Less-ordered segments remain flexible, providing extensibility.

Biomimetic and biotechnological attempts to produce spider silk

• Farming spiders fails due to practical constraints:
  • Spiders are cannibalistic.
  • Requires large space and difficult milking (yields vary by spider).
  • Scarcity drives high cost.
• Gene-based production efforts mentioned:
  • DuPont (late 1990s): spider-silk genes into E. coli and yeast.
  • Germany (2001): spider silk genes into plants like tobacco and potatoes.
  • Nexia (Canadian company): genetically modified spider goats to secrete proteins in milk.
• Central problem emphasized:
  • Produced proteins often don’t assemble into functional spider-like fibers without spider-like processing.
  • Differences in purification/source lead to different material forms.
• Need highlighted:
  • Industrial-scale success requires processing/assembly that recreates spider-like structure.

Transgenic silkworm approach (Kraig BioCraft Laboratories)

• Idea:
  • Use an insect already optimized for silk spinning (silkworms) to make spider silk.
• Method described:
  • Microinjection into silkworm eggs to insert spider silk genes.
  • Use piggyBac transposon (“cut-and-paste” transposable DNA) to integrate genes into the genome.
• Issue noted:
  • piggyBac integration is not highly targeted (recognizes a short DNA motif, TTAA), so spider gene insertion can occur in many genomic locations.
  • Fibers may therefore be only partially composed of spider silk proteins (percent estimates mentioned as ~6–10% in one discussion and ~60% in another claim).
• Next-generation approach:
  • CRISPR-Cas9 for targeted knock-in/knockout:
    • guide RNA specificity (about ~20 base match)
    • precise cutting at the intended locus
    • donor DNA used so repair incorporates spider silk where desired.

Competing/parallel research mentioned

• AMSilk (Germany): produces spider-silk-like proteins for fibers, coatings, powders, and hydrogels.
• Spiber (Japan): produces protein fibers via fermentation.
• Consumer/commercial usage mentioned:
  • Outdoor/clothing brands Goldwin and The North Face used versions of such fibers.

Applications Discussed

• Military:
  • US Army (2016) funding for ballistic shoe packs / layered protective panels using transgenic silk.
• Medicine:
  • Newrotex uses spider silk to help repair damaged nerves.
• Broader aspirational applications:
  • climbing ropes, parachute cords, airbags, bulletproof vests, clothing, armor, implants, nerve repair
• Production challenge emphasized:
  • “We need a lot of it.”

“Can we swing from spider silk?” experiment

• A transgenic spider silk filament assembly is used in a climbing gym.
• Demonstration attempts:
  • first: swinging from the silk
  • then: an ultimate test of hanging/swinging
• Outcome described:
  • Silk holds weight “reasonably,” but fibers can still be hazardous due to thinness (described as cutting/ripping skin).

Researchers / Sources Featured (Named in the Subtitles)

• Derek (experiment participant)
• Henry (research lab and explanation; includes references to Henry filming)
• Francois Xavier Bon (1709; silk stockings via collected spider egg sacs)
• Simon Peers
• Nicholas Godley
• Tom Holland (referenced)
• Andrew Garfield (referenced)
• Tobey McGuire (referenced)
• Henson Shaving (sponsor; featured in video)
• Kraig BioCraft Laboratories
• DuPont
• Nexia
• AMSilk
• Spiber
• Goldwin
• The North Face
• Newrotex
• University of Akron / Blackledge Spider Lab (research center mentioned)
• US Army (2016 funding)