Peptides and Plastics Combine To Create Soft, Sustainable, Electronic Materials

Using peptides and polymer chains, scientists at Northwestern University have developed a new type of flexible nano-ribbon material that can switch polarity in response to very low external voltages, allowing it to record and store digital information like a computer memory chip.

The new material is highly energy efficient, biocompatible and made from sustainable materials. The researchers believe that their soft material could give rise to new types of ultralight electronic devices, be woven into smart fabrics or be used for sticker-like medical devices. The research is published in Nature.

Combining peptides and plastics

Peptide amphiphiles are a class of peptide-based self-assembling molecules previously developed at Northwestern University. When placed in water, the self-assembling molecules form filaments made up of peptides and a lipid “tail” segment.

The secret behind the researchers’ innovative new material is replacing this lipid tail with tiny molecular fragments of a plastic, called polyvinylidene fluoride (PVDF).

PVDF is already well known for its unusual electronic properties. It is piezoelectric, meaning it can generate electrical signals when pressed or squeezed. It is also a ferroelectric plastic; ferroelectric materials contain tiny, spontaneously polarized electric dipoles in their structure that can flip their orientation when subject to an external electric field.

Most ferroelectrics used in today’s technologies are hard materials that contain rare or toxic metals, such as lead and niobium, which is what makes PVDF stand out.

“PVDF was discovered in the late 1960s and is the first known plastic with ferroelectric properties,” said lead study author Samuel I. Stupp, the Board of Trustees professor of materials science and engineering, chemistry, medicine and biomedical engineering at Northwestern University. “It has all the robustness of plastic while being useful for electrical devices. That makes it a very high-value material for advanced technologies. However, in pure form, its ferroelectric character is not stable, and, if heated above the so-called Curie temperature, it loses its polarity irreversibly.”

For their new material, Stupp’s team synthesized miniature segments of polymer containing only between three to seven vinylidene fluoride units, which were used to replace the lipid tails of the peptide amphiphiles.

“It was not a trivial task,” Stupp said. “The combination of two unlikely partners — peptides and plastics –  led to a breakthrough in many respects.”

Innovative new electroactive materials

When the miniature plastic segments were combined with the peptides, the plastic segments were effectively stabilized by the naturally-occurring beta-sheet structures formed by the peptides.

As a result, the final materials were equally ferroelectric and piezoelectric as PVDF, but were more stable, and could switch polarity using extremely low external voltages. This kind of stable polarity flipping is a crucial property for devices that are used to store information, as it can be harnessed to record data written in binary code.

“Using nanoscale electrodes, we could potentially expose an astronomical number of self-assembling structures to electric fields. We could flip their polarity with a low voltage, so one serves as a ‘one,’ and the opposite orientation serves as a ‘zero’. This forms binary code for information storage,” Stupp said. “Adding to their versatility, and in great contrast to common ferroelectrics, the new materials are ‘multiaxial’ – meaning they can generate polarity in multiple directions around a circle rather than one or two specific directions.”

The researchers also found that various mutations in the peptide sequence could be used to further tune the ferroelectric properties of their new material.

A breakthrough for low-power electronics

This new breakthrough in soft ferroelectric materials is exciting for multiple reasons, the researchers said. Firstly, compared to other hard ferroelectric materials – and even soft ones such as PVDF – the new material requires incredibly low voltages to flip their polarity.

“The energy required to flip their poles is the lowest ever reported for multiaxial soft ferroelectrics,” Stupp said. “You can imagine how much energy this will save in increasingly energy-hungry times.”

The new materials are also more sustainable than other ferroelectric plastics, as they are more biodegradable and lend themselves to being reused without the need for harmful solvents or high-energy recycling processes.

With further development, the researchers believe that this new type of soft ferroelectric material could be used to create energy-efficient microscopic memory chips, sensors and energy storage units. They could also be combined with other technologies, such as smart textiles, to create new wearable devices.

“We imagine a future where you could wear a shirt with air conditioning built into it or rely on soft bioactive implants that feel like tissues and are activated wirelessly to improve heart or brain function,” Stupp said.

“It’s not practical to put hard materials into our organs or in shirts that people can wear. We need to bring electrical signals into the world of soft materials. That is exactly what we have done in this study.”

“We are now considering the use of the new structures in non-conventional applications for ferroelectrics, which include biomedical devices and implants as well as catalytic processes important in renewable energy,” Stupp continued. “Given the use of peptides in the new materials, they lend themselves to functionalization with biological signals. We are very excited about these new directions.”

Reference: Yang Y, Sai H, Egner SA, Qiu R, Palmer LC, Stupp SI. Peptide programming of supramolecular vinylidene fluoride ferroelectric phases. Nature. doi: 10.1038/s41586-024-08041-4

This article is a rework of a press release issued by Northwestern University. Material has been edited for length and content.