As reported in Science Daily, researchers at Tufts University School of Engineering in Massachusetts, USA, have developed silk materials that can wrinkle into highly detailed patterns (such as words, textures, a QR code or a fingerprint) and then be erased by flooding the silk’s surface with vapour.  

In part, the process involved fabricating 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 vapour causes the fibres to relax and the wrinkles to flatten. After erasing a pattern with vapour, the textured silk can be regenerated with a cycle of heating and cooling. The authors demonstrated the ability to print patterns over at least 50 cycles, without any diminishment in contrast or resolution.

"We can print patterns of remarkably high resolution in the silk, and we even showed that we can pick up the moisture pattern left by a fingerprint," said Yu Wang, post-doctoral fellow in the Tufts University School of Engineering, and first author of the study. "But beyond the novelty of reversible printing, there are many other functional applications that the silk patterning technology could provide."

Findings were published recently in the Proceedings of the National Academy of Sciences.