Spider silk outperforms almost all man-made textiles. It has both high extensibility and tensile strength, meaning that it can be stretched a great deal before the stress causes it to break. Now, taking inspiration from another creepy-crawly creature, materials scientists have found a way to make spider silk even tougher by impregnating it with small amounts of metal. Their method, described in a paper published this afternoon in the journal Science, should work with other biomaterials too.
Since the 1980s, materials scientists have hypothesized that some protein-based natural materials, including the jaws of the marine worm Nereis, gain strength from the incorporation of metals such as zinc and copper. But until now, incorporating metals into proteins in the lab has proved challenging. Researchers at the Max Planck Institute of Microstructure physics used atomic-layer deposition to pulse zinc, titanium, and aluminum ions into spider silk. The resulting materials have greatly enhanced toughness over natural spider silk and could be used to make protective clothing or even new structural materials. To demonstrate that the method is a general one, they also used metal ions to toughen eggshell membranes, which are mostly made up of the protein collagen.
The researchers aren’t certain just how the metal ions are incorporated into the protein structure. However, they found that the protein-metal composites are tougher than the sum of their parts, which is in keeping with other recent research in biomaterials. Materials scientists looking to nature for inspiration have previously found that many of the strongest biomaterials are composites with nanoscale structural features. For example, researchers recently made a tough ceramic by mimicking the nanoscale structure of mother-of-pearl. The natural material combines brittle, bricklike layers of calcium carbonate held together with a soft but elastic protein glue. The resulting material is tougher than either constituent.