Researchers at Cornell University say they have made significant advances toward a polymer of silkworm silk that both mimics and improves on nature.
According to Dotsevi Sogah, professor of chemistry and chemical biology at Cornell, ‘We have created materials in the laboratory having properties that far exceed the natural system.’
In the 1950s, Nobel laureate Linus Pauling deduced the basic structure of silkworm silk. Within the crystalline structure in silk there is a regular protein-folding pattern, induced by amino acids, in which the molecular chain falls back and forth on itself creating the material’s elasticity.
‘We asked ourselves,’ says Sogah, ‘can we design materials that will have a similar property, although will not have all the amino acid sequences known in the protein? If we could do that, we could make the material in the lab.’
Sogah’s group sidestepped the amino acids by creating a molecular hybrid of natural and manmade structures. They did this by creating what Sogah calls ‘a biomolecular Lego set’ in which natural molecules from silk were combined with synthetic molecules ‘block by block’ in a hard and soft sequence. In this way, the team has created novel materials that are extremely flexible, strong and water soluble.
‘We wanted to get materials that would retain or exceed the properties of naturally existing ones,’ Sogah says. As an example, the average elasticity of lab samples is 300% of normal size before breaking, and one sample was stretched by 600%. ‘Other than rubbers, which are lacking in tensile strength, very few other materials have that combination of elasticity and strength,’ Sogah notes.
Early applications for the materials, says Sogah, are likely to be in textiles, where elasticity and strength are required (bulletproof vests would be a possible product). Biomedical applications are also on the horizon because of the possibility of creating a material compatible with the human biological system. ‘We could, perhaps, take silk molecular sequences and mix them with organic materials and incorporate drugs.
The material would then expand and contract for drug delivery,’ Sogah says.
Encouraged by its ability to assemble a ‘toolbox of building blocks’ of molecules, Sogah’s group is now looking at applying its ‘Lego sets’ to other materials. ‘We want to understand the principles behind this so we can dial in the properties we want. We are trying to improve on nature,’ Sogah says.