From light to logic

University of Pittsburgh

Researchers from McMaster University and the University of Pittsburgh have created the first functionally complete logic gate – a NAND gate (short for “NOT AND”) – in a soft material using only beams of visible light. The discovery, published in Nature Communications, marks a significant advance in the field of materials that compute, in which materials themselves process information without traditional electronic circuitry.

“This project has been part of my scientific journey for over a decade,” said first author Fariha Mahmood, who began studying the gels as an undergraduate researcher at McMaster and is now pursuing postdoctoral research at the University of Cambridge. “To see these materials not only respond to light but also perform a logic operation feels like watching the material ‘think.’ It opens the door to soft systems making decisions on their own.”

Mahmood is joined by authors Anna C. Balazs, distinguished professor of chemical and petroleum engineering, and Victor V. Yashin, research assistant professor at Pitt’s Swanson School of Engineering; and corresponding author Kalaichelvi Saravanamuttu, professor of chemistry and chemical biology at McMaster.

The group demonstrated that shining three self-trapped light beams into a specially engineered hydrogel can execute a NAND logic operation, one of the most fundamental building blocks of computing. Because all other digital logic gates can be built from NAND, the achievement establishes soft, photoresponsive materials as a realistic platform for autonomous, computation-capable systems.

A Material that Computes, Not Just Responds

The work builds directly on early theoretical and computational studies by Balazs and her Swanson School collaborator, the late Steven P. Levitan, professor of electrical and computer engineering, who passed away in 2016. Their landmark papers (including a 2016 Science Advances study) introduced the idea that oscillating chemical gels and other responsive materials could act as networks that sense, communicate, and compute. The latter work also involved the efforts of Yan Fang, Levitan’s graduate student at the time (now Assistant Professor at Kennesaw State University ), and Dr. Victor Yashin, a researcher in the Balazs group.

Those studies laid the conceptual groundwork for “materials that compute” – systems in which the material and the computer are the same entity, capable of performing tasks such as pattern recognition, synchronization, or decision-making without traditional circuitry.

“This is what we’ve always imagined – materials that don’t just respond to a stimulus, but process it,” Balazs said. “It’s a beautiful realization of a concept we began exploring more than a decade ago, that soft materials, through their own internal physics and chemistry, can carry out simple operations typically done by electronics.”

How Light Becomes Logic

The material at the center of the breakthrough is a merocyanine-functionalized hydrogel that contracts when illuminated. When a laser beam enters the gel, the local contraction increases the refractive index, causing the beam to “self-trap” – narrowing and brightening as it travels through the material.

In earlier work, Saravanamuttu and others found that two beams of light in the same gel compete, each inhibiting the other’s ability to self-trap. This tug-of-war behavior becomes richer when additional beams are added.

“With three beams, we began to see consistent patterns of interaction that weren’t visible before,” 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.”

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.

“It’s exciting that just three beams of light and a polymer network can map directly onto a Boolean logic operation,” Saravanamuttu added. “You don’t need wires, electrodes, or external circuits. The material processes the inputs and determines the output entirely by its internal dynamics.”

Simple Yet Elegant Decision-Making

While this system cannot compete with semiconductor processors in speed or data density, nor is it intended to, the implications are profound for fields where materials must make decisions independently:

• Soft robotics
• Self-regulating medical devices
• Sensors in inaccessible environments
• Adaptive materials that respond and reconfigure themselves

“These systems don’t aim to replace silicon – they aim to mimic the remarkable autonomy of biological materials,” Balazs said. “A soft material that can sense, compute, and respond on its own opens entirely new design spaces.”

The study also establishes 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 can be routed, combined, or cascaded without wiring.

For Balazs, the work is also a personal milestone, bringing full circle the ideas she developed with Levitan. “Steven believed deeply that materials could someday compute,” she said. “To see that vision realized experimentally is incredibly meaningful.”

Reference
A functionally complete logic gate in a soft photoresponsive hydrogel

Fariha Mahmood, Victor V. Yashin, Anna C. Balazs & Kalaichelvi Saravanamuttu

https://www.nature.com/articles/s41467-025-64960-4