Most synthetic materials are made to do just one or two things. Once they are created, their properties rarely change.
A research team at Penn State is trying to change that idea by developing a new kind of “smart synthetic skin” that can respond, adapt and even hide information—much like the skin of an octopus.
Led by Hongtao Sun, an assistant professor of industrial and manufacturing engineering, the researchers created a soft material made from hydrogel, a water-rich substance similar to jelly.
What makes this material special is that it can be programmed during printing to change how it looks, feels and moves when exposed to things like heat, liquids or physical stretching.
The work was published in Nature Communications and highlighted by the journal’s editors.
The inspiration came from cephalopods such as octopuses and squids, which can rapidly change the color, texture and shape of their skin to camouflage themselves or communicate.
Unlike animals, synthetic materials usually cannot do this. Sun’s team wanted to capture some of that biological flexibility in a man-made material.
To do this, the researchers used a technique called 4D printing. While 3D printing creates objects with a fixed shape, 4D printing adds another dimension: time.
The printed object can change its shape or appearance later in response to the environment.
The key innovation lies in how the team “programmed” the hydrogel. They used a halftone printing method, similar to the tiny dot patterns used in newspapers, to encode digital information directly into the material.
These microscopic patterns act like instructions, telling different parts of the hydrogel how much to swell, soften or bend when conditions change.
One striking demonstration involved hiding an image of the Mona Lisa inside the material. When the hydrogel film was rinsed with ethanol, the image disappeared and the film looked clear.
When placed in ice water or slowly heated, the image gradually appeared. The same hidden image could also be revealed by gently stretching the material and analyzing how it deformed.
Beyond hiding images, the smart skin can also change shape. A flat sheet can bend into dome-like or textured forms without using multiple layers or different materials.
Even more impressively, the researchers showed that shape changes and image reveals can happen at the same time, allowing appearance and movement to be coordinated within a single soft sheet.
The team believes this technology could one day be used for adaptive camouflage, secure information storage, soft robotics, biomedical devices and other advanced applications. Their next goal is to develop a scalable platform that allows many different functions to be digitally encoded into one flexible material.
By combining biology-inspired design with advanced manufacturing, this smart skin points toward a future where materials are no longer passive, but responsive, adaptable and surprisingly intelligent.
