Looking to Nature to Coat Nanomaterials

November 5, 2007

If you google “nanotechnology,” it’s hard not to be filled with awe at the nano revolution to come. According to a 2001 National Science Foundation report, “Over the next 10 to 20 years, nanotechnology will fundamentally transform science, technology, and society.”  The Institute of Global Futures declared, “Nanotechnology is a continuation of the next chapter in the acceleration of advanced technology and, perhaps more importantly, it may point to the transformation of the future global economy.”  Yet, as scientists today roll out the first wires, cubes, and other nanomaterials assembled from particles as small as one billionth of a meter, they will need to solve numerous practical issues to enable the revolution to proceed.  A sometimes overlooked but important one is how best to coat the nanomaterials and protect them from external damage.  As those in the field will tell you, they face an engineering trade off.  The nanocoatings must be tough enough to protect the materials from abrasive or blunt force.  But like the plastic protecting a phone cord, the nanocoatings must be durable enough to ensure the flexibility of the nanomaterial underneath. 

In the September issue of the journal Nature Materials, NIDCR grantees and colleagues look to marine mussels for clues into designing a tough but flexible nanocoating that resists cracking under pressure.  Mussels have an extraordinary natural ability to attach to rocks and other items in water and remain in place as the intensity of wind and wave increase.  They do so in large part by producing numerous byssal threads that act as tethers.  In the study, the scientists examined for the first time the microstructure of the cuticle coatings that protect the byssal threads of two species of mussel, Mytilus galloprovincialis and Perna canaliculus.  They found the coatings exhibited a hardness and stiffness comparable to engineering plastics but were remarkably tensile.  “When a byssal thread from P. canaliculus was stretched, its cuticle began to crack at a strain of about 30 percent,” the authors wrote.  But in M. galloprovincialis, they found cuticle rupture occurred at a remarkable 70 percent strain.  “Evidently rupture occurs through a mechanism of microtear coalescence, suggestive of the ductile fracture process in metallic alloys,” they noted.  “The granules thereby endow the cuticle with enhanced damage tolerance and hence provide protection to the underlying thread during large strain deformation.”