Tufts University scientists have developed new silk materials that can be wrinkled into highly detailed patterns such as words, textures and images.
The patterns, which take about one second to form, can be erased by flooding the surface of the silk with vapor, allowing the researchers to ‘reverse’ the printing and start all over again.
According to the scientists, these smart textiles takes advantage of the natural ability of silk fiber proteins to undergo a change of conformation in response to external conditions.
For instance, water and methanol vapor can soak into the fibers and interfere with hydrogen bond cross links in the silk fibroin, causing it to partially ‘unravel’ and release tension in the fiber.
The researchers have taken advantage of this property in particular to fabricate a silk surface from dissolved fibroin by depositing it onto a thin plastic membrane (PDMS).
After a cycle of heating and cooling, the silk surface of the silk/PDMS bilayer folds into nanotextured wrinkles due to the different mechanical properties of the layers.
Exposing any part of that wrinkled surface to water or methanol vapor causes the fibers to relax and the wrinkles to flatten.
According to the scientists, the material’s smooth surface transmits more than 80% of light, while the wrinkled surface only allows 20% or less through, creating a visible contrast and the perception of a printed pattern.
The surface can be moreover selectively exposed to vapor using a patterned mask, resulting in a matched pattern in the textured silk.
Patterns can also be created by depositing water using inkjet printing.
UV exposed parts too remain wrinkled when treated with vapor, while the parts not exposed to UV absorb the vapor and flatten out.
After erasing a pattern with vapor, the textured silk can be regenerated with a cycle of heating and cooling.
The authors have so far demonstrated the ability to print patterns over at least 50 cycles, without noticing any diminishing in contrast or resolution.
The study has also demonstrated how the patterns can be switched on and off at will by connecting the bilayer to a small electrical heating element.
This helps the silk to transition between wrinkled and wrinkle-free states.
Image and content: Fio Omenetto/Tufts University