Using beams of visible light, researchers from McMaster University and the University of Pittsburgh created a functionally complete logic gate from a soft material. The team built a NAND (not and) gate, a basic building block of computing, based on the interactions of three self-trapped beams shined on a specially engineered hydrogel. This achievement shows that materials are capable of processing information without electronic circuitry, and highlights the potential of light as a computational element. It also establishes soft, photoresponsive materials as a realistic platform for autonomous, computation-capable applications like self-regulating medical devices and soft robotics, according to the researchers. The researchers used a merocyanine-functionalized hydrogel material. When they illuminated the gel with a laser beam, the beam triggered a localized contraction in the gel that increased the refractive index, causing the beam to self-trap. The beam narrowed and brightened as it traveled through the gel. A central signal beam is always launched into the sample. Inputs A (MA) and B (MB) may be on or off. After the beams equilibrate, the final intensity profile is used to determine the output. False is only obtained when the output signal is affected by interactions with two neighboring beams. For 1 NAND 1, the output signal results from mutual interactions between Beams 1 and 3, and thus, the NAND response is false. Courtesy of Kalaichelvi Saravanamuttu. In earlier work, the researchers observed that two beams of light traveling through the same material compete, inhibiting each other’s ability to self-trap. This tug-of-war behavior became more robust when additional beams were added. Light-induced changes to the refractive index in one region suppressed contraction (and refractive index changes) elsewhere. This inhibited self-trapping and reduced the power of the central beam, which competed with two equidistant neighbors, compared to either peripheral beam, which competed with just one neighbor. The researchers exploited this geometry-dependent inhibition to create a NAND gate — the gate from which all other digital logic gates can be built. “With three beams, we began to see consistent patterns of interaction that weren’t visible before,” researcher Fariha Mahmood said. “The middle beam is always dimmer because it’s fighting both of its neighbors. That reliable behavior is what lets us map a logic operation onto a soft material.” Self-trapped beams can influence each other, leading to interactions such as attraction, repulsion, or spiraling. As they propagate through a medium, they can be subjected to designed sequences of interactions, allowing a series of operations to be performed without external intervention. This behavior makes them useful for developing soft material platforms for complex, internally mediated logic operations. “It’s exciting that just three beams of light and a polymer network can map directly onto a Boolean logic operation,” professor Kalaichelvi Saravanamuttu said. “You don’t need wires, electrodes, or external circuits. The material processes the inputs and determines the output entirely by its internal dynamics.” The researchers demonstrated two and, separately, 12 sequentially chained NAND operations. They also proposed a framework that could allow multiple logic operations to occur simultaneously inside the same gel sample. Because the input and output signals are all beams of light, they could be routed, combined, or cascaded without wiring. While this new approach to computing is not intended to compete with semiconductor processors in speed or data density, it could provide computational capabilities to applications that function and make decisions independently. Advanced materials that can process and compute with external stimuli, mimicking the sophisticated stimuli-responsiveness of biological systems, could serve as powerful platforms in applications ranging from sensors located in inaccessible areas, to therapeutics that self-guide drug release to designated areas in the body. “These systems don’t aim to replace silicon — they aim to mimic the remarkable autonomy of biological materials,” professor Anna C. Balazs said. “A soft material that can sense, compute, and respond on its own opens entirely new design spaces.” Saravanamuttu emphasized the study’s broader significance. “What excites me is the framework this establishes. We’re showing that computer logic — something we usually think of as the domain of electronics — can be carried out by a material through its own chemistry and physics. It’s a very different way of thinking about how materials can function.” The research was published in Nature Communications (www.doi.org/10.1038/s41467-025-64960-4).