A research team from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has drawn inspiration from hair to develop a 3D printable textile that changes its form based on moisture exposure using a shape memory concept. As even the most coiffed hair often becomes curly or frizzy when exposed to water or moisture, the 3D printed material can be engineered with its own shape memory.
Interestingly, hair is involved in this project in another way: the 3D printable material is itself made from keratin, a fibrous protein derived from hair, nails and shells. In SEAS’ work, it used keratin taken from leftover Agora wool from the textile manufacturing industry.
The goal of the project is to produce a biocompatible textile that could essentially shrink or expand to fit the wearer. The material, made from leftover wool, could also help to reduce waste in the fashion industry and change the way materials like wool are used. The researchers say it could even be used in the medical sector.
“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,” explained Kit Parker, the Tarr Family Professor of Bioengineering and Applied Physics at SEAS and senior author of the study. “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.”
At the foundation of the research team’s work is keratin’s structure, which comprises a single chain in the shape of a spring-like structure (aka an alpha-helix). When two of these chains twist together, it forms a coiled coil; many coiled coils form protofilaments and, ultimately, large fibers. This structure gives keratin strength and also shape memory, meaning that when a fiber is exposed to a particular stimulus, the spring-like structure uncoils. When it is exposed to another stimulus, it coils back into its original shape.
In a study published in the journal Nature Materials, the SEAS team demonstrated its work by 3D printing a series of keratin sheets in different shapes. Each sheet was programmed to have a permanent shape using a solution of hydrogen peroxide and monosodium phosphate. After that, the same sheet could be re-programmed.
In one example, the team set the permanent shape of a 3D printed sheet as a complex origami star. When the star was submerged in water, it unfolded and became malleable. Next, they rolled the sheet into a tight tube form and let it dry to form a stable, functional tube structure. When the tube was re-submerged in the water, the sheet formed itself back into an origami star.
Luca Cera, a postdoctoral fellow at SEAS and first author of the paper, said of the process: “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. This makes the material suitable for a vast range of applications from textile to tissue engineering.”
The research team says the shape-changing material could be used for wearables, such as adaptable bras, or for medical applications. “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,” Parker concluded. “We are continuing to reimagine textiles by using biological molecules as engineering substrates like they have never been used before.”