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May 01, 2009

Metalized Spider Silk Up to Ten Times Stronger


Strength for spider silk with metals added using Atomic Layer Deposition. Ten times stronger with titanium, nine times with aluminium and five times stronger with zinc.

New Scientist and the article in the Journal Science report that : the team fired beams of ionised metal compounds at lengths of silk from the orb-weaving spider Araneus diatematus using a technology called atomic layer deposition (ALD). As well as coating each silk fibre in a fine metal oxide, some metal ions penetrated the fibre. They tried zinc, aluminium and titanium compounds, all of which improved the mechanical properties of the silk. "With all three metals, the fibres can hold three to four times as much weight," says Knez. The fibres also become stretchier, so that their toughness - the energy needed to break a strand - rises even more. "The work needed to break the fibre rises tenfold with titanium, ninefold with aluminium and fivefold with zinc," he says.

The same technique might beef up other biomaterials for a host of applications such as making artificial tendons from collagen.

So if adding metal proves to not be harmful then it would be possible for people to undergo a treatment that would strengthen tendons by up to ten times. There is other research to enable people to regenerate (possibly able to say regrow a limb over months) and separate work to have non-harmful steroids or myostatin inhibitors (up to 4 times more effective than steroids) to increase strength. There was concern that myostatin inhibitors would weaken tendons. There is also the possibility of gene therapy to vastly increase strength. Success in all three areas (strength enhancement, tendon toughness, and regeneration) would enable super-soldiers and disruptive levels of physical enhancement.

The team believe that the metals are reacting with the spider silk's protein structure, forming strong covalently bonded cross-links between the amino acid polymers within the silk. Normally, these polymers are only linked by weaker hydrogen bonds.

Spider silk is not a practical engineering material, but materials scientists are trying to produce artificial fibres that mimic its properties. If they succeed, the result could be super-tough textiles.

Knez thinks the technique has more immediate potential for toughening other biomaterials such as collagen. "Mechanically improving collagen using our technique might open several new possible applications, like artificial tendons."


26 page Pdf of supporting material that describe the procedure and the results. The pictures and charts and graphs in this article are from this source.








The abstract: Greatly Increased Toughness of Infiltrated Spider Silk

In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.






[1] SS/N: Native dragline silk of Araneus spider.
[2] ESM/N: Native eggshell membrane.
[3] SS/TIP and [4] SS/W*: Native silks which are dipped into TIP (Ti [OCH(CH3)2]4) or water at ambient conditions (T=15°, P=Patm) during 10 hours, followed by drying at the same conditions, respectively.
[5] SS/TP/100 and [6] SS/WP/100: Single precursor (TMA or water) exposure during 100 cycles at the same processing condition as SS/Al2O3/100, respectively.
[7] PF/Al2O3/300 (for NMR): Para film on which Al2O3 layer is deposited at the same processing condition as SS/Al2O3/300.
* For easy preparation and handling of these samples, when we dipped the silk into TIP/water and subsequently dried silk, we used directly a paper clip on which silk fibers are wound as a sample carrier for dipping and drying. During this process, unintentionally the sample, in particular SS/W, is subjected to an axial restraint during drying at room temperature and ambient atmosphere.



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