PNNL researchers discover graphene works as scaffold for silk fibers; may contribute to next-gen bioelectronics.

Once treasured for its luxurious feel, strength, and durability, silk is now poised to take on a cutting-edge role in electronics as scientists at Pacific Northwest National Laboratory have discovered how to combine its unique properties with graphene, unlocking the potential for flexible circuits that could revolutionize everything from biodegradable sensors to advanced computing applications.

For centuries, silk production was a closely guarded secret in China, while its fame spread through the celebrated Silk Road trade routes to India, the Middle East, and eventually Europe; by the Middle Ages, silk had become a status symbol and a coveted commodity in European markets.

Silk is an extraordinary material produced by silkworms, carefully harvested from the insect's natural cocoon and then woven into fine, durable threads.

Primarily composed of fibroin, a protein that arranges itself in strong, tightly packed layers, silk derives its incredible strength from these layers, giving it a tensile strength comparable to steel – up to 1,500 megapascals – while remaining lightweight and flexible.

In addition to its strength, silk is highly elastic, capable of stretching up to 20% before breaking, which allows it to maintain both flexibility and durability, making it ideal for weaving into resilient fabrics.

Silk's strength and elasticity are remarkable enough that, in theory, a pencil-thick strand of silk could support the weight of a small car (around 1,500 pounds) without breaking. Though we don't use silk this way, its capacity to hold significant weight while stretching makes it a fascinating material with potential for high-performance applications.

While silk protein has been deployed in designer electronics, its use is currently limited in part because silk fibers are a messy tangle of spaghetti-like strands – which works well for the silkworm.

However, a research team led by scientists at Pacific Northwest National Laboratory (PNNL) has untangled the knots.

In a recent Science Advances report, researchers from Pacific Northwest National Laboratory successfully created a uniform, two-dimensional layer of silk fibroins by integrating graphene into the process.

"These results provide a reproducible method for silk protein self-assembly that is essential for designing and fabricating silk-based electronics," said Chenyang Shi, the study's lead author. "It's important to note that this system is nontoxic and water-based, which is crucial for biocompatibility."

This combination of silk and graphene offers the potential to create sensitive, tunable transistors, which are highly sought after by the microelectronics industry for use in wearable and implantable health sensors.

Beyond medical applications, the PNNL team envisions this material playing a key role in developing memory transistors, or "memristors," for neural network computing, allowing devices to simulate brain-like functions.

"There's been a lot of research using silk as a way of modulating electronic signals, but because silk proteins are naturally disordered, there's only so much control that's been possible," said James De Yoreo, a Battelle Fellow at PNNL and professor of materials science, engineering, and chemistry at the University of Washington. "So, with our experience in controlling material growth on surfaces, we thought 'what if we can make a better interface?'"

Mike Perkins; Pacific Northwest National Laboratory

Individual silk protein molecules, or "silk fibroins" (blue), are deposited on a graphene surface surrounded by water (green and red spheres) and grow into an atomically precise two-dimensional (2D) sheet.

To achieve better control over the formation of silk proteins, the researchers meticulously regulated the conditions of the assembly process, layering individual silk fibers onto a graphene template within a water-based system. This process allowed the silk fibroin proteins to organize themselves into a precise, two-dimensional structure.

Due to the unique electrical and structural properties of graphene, it facilitated the alignment of silk proteins into well-organized, parallel structures, similar to those found in natural biological systems.

Through further imaging studies and complementary theoretical calculations, the PNNL researchers confirmed that the thin layer adopted a stable, organized structure with features similar to those found in natural silk.

At less than half the thickness of a strand of DNA, this electronically-capable structure is perfectly suited for the level of miniaturization necessary in future bioelectronics, where small, precise components are crucial.

"This type of material lends itself to what we call field effects," said De Yoreo. "This means that it's a transistor switch that flips on or off in response to a signal. If you add, say, an antibody to it, then when a target protein binds, you cause a transistor to switch states."

Building on this initial breakthrough, the research team plans to refine the process by engineering artificial silk enhanced with functional proteins tailored for specific applications. This would open the door for even more precise and adaptable electronics.

As they move forward, other research areas will focus on improving both the stability and conductivity of silk-based circuits, with an eye toward developing biodegradable electronics that could dramatically reduce the environmental impact of electronic waste – advancements that could play a pivotal role in establishing green chemistry practices as the foundation for the next generation of sustainable electronic manufacturing.