Japanese scientists develop new plastic-like materials that fully degrade in the sea

Artistic rendering of the new plastic. Cross linked salt bridges visible in the plastic outside the seawater give it its structure and strength. In seawater (and in soil, not depicted), resalting destroys the bridges, making it water soluble, thus preventing microplastic formation and allowing the plastic to become biodegradable. © 2025 RIKEN

Microplastics—tiny plastic particles smaller than 5 millimeters—have spread to nearly every part of the Earth, reaching even the most isolated areas like the deep ocean, the Arctic, and even the air around us.

These particles are increasingly being detected within the human body, including in our bloodstream and brain. Although the full extent of their impact on human health and the environment remains unclear, microplastics are already known to disrupt marine and land ecosystems, leading to issues such as stunted animal growth, reduced fertility, and organ damage.

Seawater solution

RIKEN scientists are working on a solution to ocean microplastic pollution by developing a new material that breaks down naturally in saltwater.

According to Takuzo Aida, a materials scientist leading the Emergent Soft Matter Function Research Group at the RIKEN Center for Emergent Matter Science in Wako, Japan, this innovative material matches traditional plastics in terms of weight and durability. It holds promise not only for cutting plastic pollution but also for reducing greenhouse gas emissions linked to plastic incineration.

This breakthrough is the result of Aida’s 30 years of pioneering research in the field of supramolecular polymers—materials made from molecules linked by weaker, reversible bonds, unlike conventional plastics, which rely on strong covalent bonds that require significant energy to break.

Aida compares these reversible bonds to sticky notes that can be attached and removed with ease. This structure gives supramolecular polymers remarkable qualities, such as self-healing when broken and rejoined, as well as being highly recyclable. Specific solvents can break the bonds at the molecular level, making these materials easy to reuse and repurpose.

A thin square of the glassy new plastic © 2025 RIKEN

Unlocking bonds

Plastic is so widely used for a reason, says Aida. “Plastics, especially polyethylene terephthalate (PET), commonly used in bottles, offer exceptional versatility. They’re tough yet flexible, durable, and recyclable qualities that make them incredibly convenient and hard to replace.”

While biodegradable plastics are often proposed as alternatives, Aida points out that their decomposition speed and required conditions are significant limitations. For example, polylactic acid (PLA)—a plastic designed to break down in soil—has been found largely intact in the ocean because it degrades too slowly under typical environmental conditions. Since PLA isn't water-soluble, it eventually fragments into microplastics, which can’t be broken down by microbes like bacteria or fungi.

Concerned about the environmental impact, Aida turned to supramolecular materials in hopes of addressing these issues. “The challenge is that while supramolecular polymers have reversible bonds, which makes them adaptable, it also makes them prone to falling apart too easily,” he explains, limiting their practical use.

To solve this, his team searched for a compound combination that could deliver both durability and rapid breakdown under specific conditions, leaving behind only harmless byproducts. Aida envisioned a mechanism where the polymer’s structure could be stabilized,but unlocked by a specific trigger—salt.

After testing various molecules, the team discovered that mixing sodium hexametaphosphate (a common food additive) with guanidinium ion-based monomers (found in fertilizers and soil enhancers) produced strong “salt bridges.” These bridges formed durable cross-linked bonds that gave the material both strength and flexibility. According to Aida, these bonds act like a lock that only salt can open.

Screening molecules can feel like searching for a needle in a haystack," Aida says. "But we discovered the right combination early on, and it made us think, ‘This could actually work.’"

In their research, Aida’s team created a small sheet of this supramolecular material by mixing the compounds in water.

The solution naturally separated into two layers—one viscous at the bottom and watery at the top, which was an unexpected outcome. The viscous bottom layer contained the compounds bonded by salt bridges. This layer was collected and dried to form a plastic-like sheet.

Not only was the sheet as strong as traditional plastics, but it was also colorless, transparent, and non-flammable, offering great flexibility. More importantly, the sheet broke down into its original materials when immersed in saltwater, as the electrolytes in the saltwater disrupted the salt bridge ‘locks.’ The team’s tests showed that the sheet disintegrated after just 8.5 hours in saltwater.

Additionally, the sheet can be made waterproof with a hydrophobic coating. Even when waterproofed, the material can still dissolve quickly if its surface is scratched, allowing salt to penetrate, Aida explains.

Driving change

Not only is the supramolecular material biodegradable, but Aida also envisions that its byproducts could be repurposed. When broken down, the new material leaves behind nitrogen and phosphorus, which can be metabolized by microbes and absorbed by plants, he explains.

However, Aida warns that this requires careful management. While these elements can benefit soil, they could also lead to nutrient overload in coastal ecosystems, potentially causing algal blooms that disrupt entire environments. The ideal solution may be to recycle the material primarily in a controlled facility using seawater, allowing the raw materials to be recovered and used to produce supramolecular plastics again.

Beyond creating alternatives to fossil fuel-based plastics, Aida stresses the need for decisive action from governments, industries, and researchers to drive meaningful change. Without stronger measures, global plastic production—and the related carbon emissions—could more than double by 2050.

“The plastics industry faces a significant challenge due to established infrastructure and factory lines,” says Aida. “But I believe there will come a tipping point where we must push through that change.” Technologies like this, he believes, will be crucial when that time arrives.