A team of scientists from the University of Chicago and Michigan State University, among others, has developed a new approach that uses hydrogel to function as a unique, unclonable physical signature to prevent the counterfeiting of medical implants, microchips and other devices, which can threaten lives, money and security.

While conventional digital encryption is used to protect data, the team explained that it cannot verify physical items. Likewise serial numbers, barcodes and holograms can be replicated if someone knows the fabrication details.

To create a solution to this issue of counterfeiting objects and devices, the team turned the hidden structure of a soft, conductive hydrogel into a measurable signal that cannot be duplicated.

To accomplish this, a process dubbed regional assembly crosslinking (RAC) was used to fabricate a hydrogel from the combination of two polymers: polypyrrole (PPy), which conducts electricity, and polystyrene sulfonate (PSS), which carries ions and provides flexibility.

As the hydrogel forms, the mix is exposed to an electric field that causes the PPy and PSS to separate into tiny regions, thereby forming thousands of junctions where electrons and ions interact.

The team explained that each junction behaves slightly differently, creating a complex 3D network that is almost impossible to replicate exactly. These ion-electron transduction junctions behave like microscopic gates for electrical charge.

When electrical pulses are sent through the hydrogel, the pulses travel through the network in a way that relies on the unique microscopic structure of the gel. Even if the same set of electrical pulses is repeated 1,000 times, the hydrogel creates almost identical responses, which demonstrates its high reliability.

“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 noted.

The voltage rises and falls quickly, with the gel reaching 90% of its peak in a mere 13 milliseconds and dropping to 10% in roughly 49 milliseconds, which is an indication of efficient charge transfer.

The hydrogel’s design creates a significant challenge space: on an 8×8 grid of pulses, the number of possible input patterns is 2⁶⁴, or roughly 10 quintillion. This is reportedly far more than earlier physical unclonable functions (PUFs), thus making it almost impossible for an attacker to guess or copy.

The team suggests that the approach promises a new path to secure authentication with the RAC hydrogel functioning like a physical fingerprint for materials.

In addition to safeguarding microchips and medical implants, this technology could potentially protect flexible electronics, wearable sensors and smart packaging.

This new material is detailed in the article, “Tailoring Topological Network of Conductive Hydrogel for Electrochemically Mediated Encryption,” which appears in the journal Advanced Materials.