Wool-like material can remember and change shape
Material could be used in smart textiles, medical devices and more

Date:
September 3, 2020
Source:
Harvard John A. Paulson School of Engineering and Applied Sciences
Summary:
Researchers have developed a biocompatible material that can
be 3D printed into any shape and pre-programmed with reversible
shape memory.

The material is made using keratin, a fibrous protein found
in hair, nails and shells, extracted from leftover Agora wool
used in textile manufacturing. It could be used in anything from
self-fitting bras to actuating textiles for medical therapeutics
and could help reduce waste in the fashion industry.



FULL STORY ==========================================================================
As anyone who has ever straightened their hair knows, water is the
enemy. Hair painstakingly straightened by heat will bounce back into curls
the minute it touches water. Why? Because hair has shape memory. Its
material properties allow it to change shape in response to certain
stimuli and return to its original shape in response to others.


==========================================================================
What if other materials, especially textiles, had this type of shape
memory? Imagine a t-shirt with cooling vents that opened when exposed
to moisture and closed when dry, or one-size-fits-all clothing that
stretches or shrinks to a person's measurements.

Now, researchers at the Harvard John A. Paulson School of Engineering
and Applied Sciences (SEAS) have developed a biocompatible material that
can be 3D- printed into any shape and pre-programmed with reversible
shape memory. The material is made using keratin, a fibrous protein
found in hair, nails and shells. The researchers extracted the keratin
from leftover Agora wool used in textile manufacturing.

The research could help the broader effort of reducing waste in the
fashion industry, one of the biggest polluters on the planet. Already, designers such as Stella McCarthy are reimagining how the industry uses materials, including wool.

"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 Kit Parker, the Tarr Family Professor of Bioengineering and Applied Physics at SEAS and senior author of the
paper. "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 research is published in Nature Materials.

The key to keratin's shape-changing abilities is its hierarchical
structure, said Luca Cera, a postdoctoral fellow at SEAS and first author
of the paper.



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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 fibers.

"The organization of the alpha helix and the connective chemical bonds
give the material both strength and shape memory," said Cera.

When a fiber is stretched or exposed to a particular stimulus, the
spring-like structures uncoil, and the bonds realign to form stable beta-sheets. The fiber 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 --
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 re-programmed and molded
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 fibers like this to make brassieres whose cup size and shape can be customized 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."

========================================================================== Story Source: Materials provided by Harvard_John_A._Paulson_School_of_Engineering_and_Applied
Sciences. Original written by Leah Burrows. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Luca Cera, Grant M. Gonzalez, Qihan Liu, Suji Choi, Christophe O.

Chantre, Juncheol Lee, Rudy Gabardi, Myung Chul Choi, Kwanwoo
Shin, Kevin Kit Parker. A bioinspired and hierarchically
structured shape-memory material. Nature Materials, 2020; DOI:
10.1038/s41563-020-0789-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200903155506.htm

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