The researchers, from the Beckman Institute at the University of Illinois Urbana-Champaign, developed a new technique that mimics the biological processes behind the formation of the ridges on our fingertips, or the spots on a cheetah. They hope it could simplify relatively complex manufacturing processes, such as the multi-step synthetic procedure, casting and moulding required to make a simple water bottle.
“When you build a house, you have to build every room in the house. But when you're making a body, nobody's putting the arms and the legs in the right place – it just happens,” said research co-leader Elizabeth Feinberg. “We wanted to know if we could do things more like nature, rather than how we typically do it ourselves.”
In general, complex patterns integral to the structure and function of biological materials arise spontaneously during morphogenesis, a biological process that causes a cell, tissue or organism to develop its shape.
Functional patterns in synthetic materials, on the other hand, are typically created through multistep manufacturing processes, making it difficult to change how materials are patterned.
“It's very hard to get patterns into materials, but throughout biology we see patterns with a large number of uses, from mechanical performance to camouflage,” said co-leader Evan M Lloyd. “We wanted to see if we could look at ways that patterns could emerge spontaneously.”
The first step was to use a relatively new manufacturing technique known as frontal polymerisation, a reaction-thermal diffusion system that utilises the diffusion of heat to promote chemical reactions. Under certain conditions, the chemical reaction produces regions with varying degrees of heat. The team took advantage of these properties to change polymer microstructure and mechanical properties, and subsequently fine-tuned the reactions based on the applications of heat.
Ridges generated spontaneously during free-surface frontal polymerisation of dicyclopentadiene (Credit: Autonomous Materials Systems Group, Beckman Institute)
“We can incorporate alternative chemistry that is thermally sensitive within that temperature difference regime to generate changes in colour, morphology, mechanical property,” said Lloyd. “It's really all about how we can translate changes in reaction temperature and see lasting material properties.”
The result achieved is essentially the varying stiffness of materials, said Beckman Institute director Jeff Moore.
Manufacturing materials created with this method could be implemented on a large scale within a few decades, Feinberg predicted. They could be used in mundane, everyday items like desks, or in massive products like windmills or aeroplane fuselages.
The results could be ‘monumental’ for sustainable manufacturing, a research announcement said.
“When you cure a polymer, you have to thermally cure it at 100ºC or more, and it has to bake for hours. That takes a lot of energy,” said Feinberg. “But here, because the way frontal polymerisation works, you apply energy to just one small spot and it propagates or releases the latent energy in the chemical precursor. It requires a lot less energy to get it going.”
By introducing more multi-functional materials, the process could also reduce the number of single-use materials needed in manufacturing, Lloyd said.
The project was imagined by aerospace engineering professor Scott White, who mentored both Feinberg and Lloyd before his death in 2018.
The research was published in the American Chemical Society's Central Science journal.
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