In a world where fake medical implants, counterfeit microchips, and cloned devices can threaten lives, money, and security, proving that a physical object is truly genuine is a major challenge.
Conventional digital encryption protects data, but it can’t verify physical items. Even serial numbers, barcodes, and holograms can be copied if someone knows the fabrication details.
Now, scientists have developed a novel method using a special kind of gel that can act as a unique, unclonable physical signature. The secret lies in turning the hidden structure of a soft, conductive hydrogel into a measurable signal that no one can duplicate.
The key to uncompromising security
The team built their solution using a process called regional assembly crosslinking (RAC) to make a hydrogel from two polymers: polypyrrole (PPy), which conducts electricity, and polystyrene sulfonate (PSS), which carries ions and provides flexibility.
When the hydrogel forms, the mixture is exposed to an electric field. This causes the PPy and PSS to separate into tiny regions, creating thousands of junctions where electrons and ions interact.
Each junction behaves slightly differently, forming a complex 3D network that is impossible to exactly replicate. These junctions, called ion-electron transduction junctions, act like microscopic gates for electrical charge.
When the researchers send electrical pulses through the hydrogel, the pulses travel through this network in a way that depends on the unique microscopic structure of the gel. Even if the same challenge (a set of electrical pulses) is repeated 1,000 times, the hydrogel produces nearly identical responses, showing that it’s highly reliable.
“The RAC hydrogel-based encryption device generates over 1019 challenge–response pairs, significantly surpassing the standard requirement of 1010 for a strong physical unclonable cryptographic primitive,” the study authors note.
The rise and decay of the voltage are fast. The gel reaches 90 percent of its peak voltage in 13 milliseconds and drops to 10 percent in 49 milliseconds, demonstrating efficient charge transfer.
The hydrogel’s design creates a huge challenge space. For an 8×8 grid of pulses, the number of possible input patterns is 264, or about 10 quintillion. That’s far more than earlier physical unclonable functions (PUFs), which makes it practically impossible for an attacker to guess or copy.
Even when sophisticated machine learning algorithms, including Transformers, tried to predict the gel’s responses based on thousands of samples, they failed. The hydrogel’s nonlinear and unpredictable internal dynamics prevent accurate modeling.
Why this matters and what comes next
This breakthrough opens up a new path to secure authentication. The RAC hydrogel acts like a physical fingerprint for materials, combining high reproducibility, enormous challenge capacity, and resistance to copying.
Beyond safeguarding microchips and medical implants, this technology could protect flexible electronics, wearable sensors, and smart packaging. The materials used, PPy, PSS, and simple solvents, are inexpensive, and fabrication requires only basic voltage control and laser patterning, making large-scale production feasible.
However, the technology is still in the early stages. While the hydrogel is highly resistant to attacks, extreme conditions, or long-term wear might affect its performance, and real-world testing across industries will be needed.
The researchers plan to explore embedding these hydrogels directly into products, improving stability, and scaling up production. In the future, every object could carry its own unforgeable signature, adding a layer of trust that is literally built into its molecular structure.
The study is published in the journal Advanced Materials.