“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 textiles to tissue engineering.”Luca Cera
A team from the Harvard John A. Paulson School of Engineering and Applied Sciences have developed a biocompatible material that can be 3D-printed into any shape and pre-programmed with reversible shape memory. Their breakthrough could lead to applications in smart textiles and medical devices, as well as reducing the pollution produced by the fashion industry through less waste and improved use of materials such as wool.
As described in Nature Materials [Cera et al. Nat. Mater. (2020) DOI: 10.1038/s41563-020-0789-2], the material uses keratin, a fibrous protein present in hair, nails and shell, extracted from Agora wool left over from textile manufacturing. The hierarchical structure of keratin has a single chain of structural protein arranged into a spring-like structure, and when two of the chains twist together they form a structure that combines to form protofilaments and eventually large fibers.
On being stretched or exposed to specific stimuli, the structures uncoil, with the bonds realigning to form stable beta-sheets. The fiber stays in that position until triggered to return to its original shape. The work provides a further stage on the use of proteins as building blocks to engineer smart materials that better interface and potentially chemically communicate with biological substrates.
The team 3D-printed keratin sheets in different shapes, before programming the material's permanent shape with a solution of hydrogen peroxide and monosodium phosphate. When the memory is set in this way, the sheet can be re-programmed and molded into new shapes. Such recycled keratin protein brings sustainability, and reduces the environmental impact of the fashion and textile industries.
The technique could lead to one-size-fit-all clothing designs that are also more comfortable – for instance, clothes could be designed that have cooling vents that are able to open and close based on levels of moisture, or that even stretch or shrink depending on the wearer’s measurements.
First author Luca Cera told Materials Today, “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 textiles to tissue engineering.”
The team now hopes to extend the responsiveness of the shape memory system to encompass further triggers, including heat, light and chemical messengers, and will focus on specific applications in textile and tissue engineering to implement fully functional devices based on their shape memory technology.