Science & Technology (Commonwealth Union) – Despite the fact that synthetic materials are widely in use across industries and various studies, most are engineered for only a narrow range of purposes. To overcome this limitation, a Penn State team led by Hongtao Sun, an assistant professor of industrial and manufacturing engineering, created a fabrication technique capable of producing multifunctional “smart synthetic skin.” These customizable materials can encrypt and decode information, support adaptive camouflage, power soft robotic systems and perform other advanced tasks.
With this new method, the researchers produced a programmable smart skin made from hydrogel, a water-dense, gel-like substance. Unlike conventional synthetic materials with static characteristics, this smart skin offers expanded versatility. Scientists can tune the gel’s optical properties, mechanical behavior, surface patterns and shape-changing abilities in response to external triggers such as heat, solvents or physical stress.
The group described the innovation in a paper published in Nature Communications, where it was also selected for the journal’s Editors’ Highlights.
Sun, the project’s principal investigator, said the concept was inspired by cephalopods such as octopuses, whose biological skin can rapidly alter its appearance to hide from predators or send signals to one another.
“Cephalopods use a complex system of muscles and nerves to exhibit dynamic control over the appearance and texture of their skin,” explained Sun. “Inspired by these soft organisms, we developed a 4D-printing system to capture that idea in a synthetic, soft material.”
Sun, who also has appointments in biomedical engineering, materials science and engineering, and Penn State’s Materials Research Institute, said the approach qualifies as 4D printing because it creates 3D structures that can actively respond to environmental changes. The researchers relied on a process called halftone-encoded printing, which converts images or textures into binary patterns of ones and zeros and embeds that data directly into the material — similar to the dot arrangements used in print media photography. With this method, the team can effectively program the smart skin to alter its look or surface characteristics when exposed to specific triggers.
The encoded patterns determine how different sections of the material react to their surroundings. Certain regions may shrink, swell, or soften more than others when subjected to shifts in temperature, fluids, or mechanical stress. By fine-tuning these patterns, the researchers can control the overall behavior of the material.
Sun pointed out that in simple terms, they are embedding instructions into the material and those instructions guide how the skin responds when its environment changes.
Haoqing Yang, a doctoral researcher in IME and the paper’s lead author, noted that one of the most dramatic demonstrations is the material’s capacity to conceal and reveal images. To illustrate this, the team encoded the Mona Lisa onto the smart skin. When rinsed with ethanol, the film turned transparent and the image disappeared. After being placed in ice water or gradually heated, the Mona Lisa reappeared in full detail.
Yang added that while the Mona Lisa served as a proof of concept, the technique can be used to embed virtually any image into the hydrogel.
“This behavior could be used for camouflage, where a surface blends into its environment, or for information encryption, where messages are hidden and only revealed under specific conditions,” explained Yang.
The researchers demonstrated that concealed patterns can be exposed by lightly stretching the material and tracking its deformation using digital image correlation. In other words, information doesn’t have to be accessed purely visually — it can also be decoded through mechanical strain, providing an additional layer of protection.
The material showed remarkable flexibility. According to Sun, the smart skin can shift from a simple flat sheet into unconventional, nature-inspired forms with intricate surface textures. Unlike many other morphing materials, this transformation doesn’t depend on stacked layers or mixed components. Instead, the complex shapes and textures — similar to those found on cephalopod skin — are governed by a digitally printed halftone design embedded within a single sheet.
