Wool-like material remembers and transforms back into its old shape
Image credit: unsplash
Scientists have developed a new material that can be 3D-printed into any shape and pre-programmed with reversible shape memory.
A team at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) developed the material using keratin, a fibrous protein found in hair, nails and shells which they extracted from leftover Agora wool used in textile manufacturing.
The researchers believe the new material could help to reduce waste in the fashion industry - one of the biggest polluters on the planet.
“With this project, we have shown that not only can we recycle wool, but we can build things out of the recycled wool that have never been imagined before,” said senior author Kit Parker.
“The implications for the sustainability of natural resources are clear. With recycled keratin protein, we can do just as much, or more, than what has been done by shearing animals to date and, in doing so, reduce the environmental impact of the textile and fashion industry.”
The key to keratin’s shape-changing abilities is its hierarchical structure. A single chain of keratin is arranged into a spring-like structure known as alpha-helix. Two of these chains twist together to form a structure known as a coiled coil. Many of these coiled coils are assembled into protofilaments and eventually large fibres.
“The organisation of the alpha helix and the connective chemical bonds give the material both strength and shape memory,” said researcher Luca Cera.
When a fibre is stretched or exposed to a particular stimulus, the spring-like structures uncoil and the bonds realign to form what the team calls stable beta-sheets. The fibre remains in that position until it is triggered to coil back into its original shape.
To demonstrate this process, the researchers 3D-printed keratin sheets in a variety of shapes. They programmed the material’s permanent shape - i.e. the shape it will always return to when triggered - using a solution of hydrogen peroxide and monosodium phosphate.
Once the memory was set, the sheet could be reprogrammed and moulded into new shapes.
For example, one keratin sheet was folded into a complex origami star as its permanent shape. Once the memory was set, the researchers dunked the star in water, where it unfolded and became malleable. From there, they rolled the sheet into a tight tube. Once dry, the sheet was locked in as a fully stable and functional tube. To reverse the process, they put the tube back into water, where it unrolled and folded back into an origami star.
“This two-step process of 3D printing the material and then setting its permanent shapes allows for the fabrication of really complex shapes with structural features down to the micron level,” said Cera. “This makes the material suitable for a vast range of applications, from textile to tissue engineering.”
“Whether you are using fibres like this to make brassieres whose cup size and shape can be customised every day, or you are trying to make actuating textiles for medical therapeutics, the possibilities of Luca’s work are broad and exciting,” said Parker.
“We are continuing to reimagine textiles by using biological molecules as engineering substrates like they have never been used before.”
Earlier this year, University of Manchester researchers warned that the fashion industry must make urgent and fundamental changes in order to prevent devastating environmental damage. The fashion industry is one of the world’s largest industrial polluters, yet continues to grow, in large part due to the rise of 'fast fashion' which is based on a rapid cycle of cheap, mass-manufactured, disposable garments often made from artificial fibres, driven by the popularity of budget online fashion retailers such as Asos, Boohoo and Missguided.
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