Move over Nature…the famed strength of a spider’s web silk now has some competition. Bio-mimicry and bio-materials–both emerging new sciences that seek to utilize and/or reproduce or modify natural biological materials and properties for commercial usage–has been seeing an explosion of research and experimentation of late. Recent bio-materials experiments with spider dragline silk (taken from an Araneus spider’s silk glands) have resulted in a bio-mimicked new material that is stronger than its natural version.
To make this new material, the scientists had to “infiltrate” the inner protein structure of the spider’s dragline, silk threads with a metal ion of zinc (Zn 2+). These experiments built on earlier analyses of the mandibles of leaf-cutter ants, locusts, and marine polychaetes (a type of large sea worm) that showed a strong relationship between accumulated Zinc, Aluminum and Titanium levels in these materials and their high tensile and hardness properties. Previous attempts to incorporate such metals synthetically had proven to be too great a technological challenge.
Spider silk is described as a “semi-crystalline biopolymer” (a polymer is a long chain of strongly connected, usually similar molecules) composed of a complex mix of hydrophobic (water-rejecting) crystalline molecules and non-crystalline amino acid chains, linked together by hydrogen bonds. How exactly metal particle are incorporated into the protein structure of spider silk, naturally, has remained an unanswered question. But now it seems that the question need not be answered anyways.
Reporting in a recent edition of Science (April 24, 2009), materials scientists from the Max Planck Institute and Martin Luther University (Lee, Pippel et al) describe a new technique termed multiple pulsed vapor- phase infiltration (MPI). The technique is based upon the same equipment used for atomic layer deposition (ALD) which is used in nano-tech and materials science for many other applications. Using this technique, the researchers were able to infiltrate Zn, Al and Ti particles into the protein structure of the spider silk. This is done in part by exposing the silk to a gas or vapor containing the desired metal (attached to an akyl group molecule and mixed with water vapor).
Following this infiltration technique, the scientist were able to show considerable increase in both the maximum stress capacity of the material, and what’s known as its E-modulus (or Young’s modulus), over the native version of the silk. Translation: the infiltrated silk’s “toughness” was greatly improved.
Applications for this bio-material are few so far, but the technique could also be used for strengthening collagen membranes which have valuable uses for reconstructive surgery and other medical therapeutics.
Photo / Credit: Araneus diadematus – Chfab on wikipedia – GNU
About Michael Ricciardi
