Fabrication of the nanocomposites begins by dissolving silk cocoons and making the resulting fibroin water soluble. The silk is then placed onto a silicon substrate using a spin-coating technique that produces multiple layers of thin film that is then patterned into a template using a nanolithography technique.
"Because silk is a protein, we can control the properties of the surface and design different kinds of surfaces," explained Kharlampieva. "This surface-mediated approach is flexible at producing different shapes. We can apply the method to coat any surface we want, including objects of complex shapes."
Next, the silk template is covered with a solution containing ions of gold, silver, or other metal. Over a period of time ranging from hours to days, the nanoparticles form within the template. The relatively long growth time, which operates at room temperature and neutral pH in a water-based environment, allows precise control of the particle size and spacing, Tsukruk noted.
"We operate at conditions that are suitable for biological activities," he said. "No reducing agents are required to produce the particles because the biomolecules serve as reducing agents. We don't add any chemicals that could be toxic to the protein."
Use of these mild processing conditions reduces the cost producing the composites and their potential environmental impact. When dried, the resulting silk-nanoparticle film has high tensile strength, high elasticity and toughness.
"Silk is almost as strong as Kevlar, but it can be deformed by 30 percent without breaking," said Tsukruk. "The
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Georgia Institute of Technology Research News