Microplastics are an environmental hazard found nearly everywhere on Earth, released by the breakdown of tires, clothing, and plastic packaging. Another significant source of microplastics is tiny beads that are added to some cleansers, cosmetics, and other beauty products.
In an effort to cut off some of these microplastics at their source, MIT researchers have developed a class of biodegradable materials that could replace the plastic beads now used in beauty products. These polymers break down into harmless sugars and amino acids.
“One way to mitigate the microplastics problem is to figure out how to clean up existing pollution. But it’s equally important to look ahead and focus on creating materials that won’t generate microplastics in the first place,” says Ana Jaklenec, a principal investigator at MIT’s Koch Institute for Integrative Cancer Research.
These particles could also find other applications. In the new study, Jaklenec and her colleagues showed that the particles could be used to encapsulate nutrients such as vitamin A. Fortifying foods with encapsulated vitamin A and other nutrients could help some of the 2 billion people around the world who suffer from nutrient deficiencies.
Jaklenec and Robert Langer, an MIT Institute Professor and member of the Koch Institute, are the senior authors of the paper, which appears today in Nature Chemical Engineering. The paper’s lead author is Linzixuan (Rhoda) Zhang, an MIT graduate student in chemical engineering.
Biodegradable plastics
In 2019, Jaklenec, Langer, and others reported a polymer material that they showed could be used to encapsulate vitamin A and other essential nutrients. They also found that people who consumed bread made from flour fortified with encapsulated iron showed increased iron levels.
However, since then, the European Union has classified this polymer, known as BMC, as a microplastic and included it in a ban that went into effect in 2023. As a result, the Bill and Melinda Gates Foundation, which funded the original research, asked the MIT team if they could design an alternative that would be more environmentally friendly.
The researchers, led by Zhang, turned to a type of polymer that Langer’s lab had previously developed, known as poly(beta-amino esters). These polymers, which have shown promise as vehicles for gene delivery and other medical applications, are biodegradable and break down into sugars and amino acids.
By changing the composition of the material’s building blocks, researchers can tune properties such as hydrophobicity (ability to repel water), mechanical strength, and pH sensitivity. After creating five different candidate materials, the MIT team tested them and identified one that appeared to have the optimal composition for microplastic applications, including the ability to dissolve when exposed to acidic environments such as the stomach.
The researchers showed that they could use these particles to encapsulate vitamin A, as well as vitamin D, vitamin E, vitamin C, zinc, and iron. Many of these nutrients are susceptible to heat and light degradation, but when encased in the particles, the researchers found that the nutrients could withstand exposure to boiling water for two hours.
They also showed that even after being stored for six months at high temperature and high humidity, more than half of the encapsulated vitamins were undamaged.
To demonstrate their potential for fortifying food, the researchers incorporated the particles into bouillon cubes, which are commonly consumed in many African countries. They found that when incorporated into bouillon, the nutrients remained intact after being boiled for two hours.
“Bouillon is a staple ingredient in sub-Saharan Africa, and offers a significant opportunity to improve the nutritional status of many billions of people in those regions,” Jaklenec says.
In this study, the researchers also tested the particles’ safety by exposing them to cultured human intestinal cells and measuring their effects on the cells. At the doses that would be used for food fortification, they found no damage to the cells.
Better cleansing
To explore the particles’ ability to replace the microbeads that are often added to cleansers, the researchers mixed the particles with soap foam. This mixture, they found, could remove permanent marker and waterproof eyeliner from skin much more effectively than soap alone.
Soap mixed with the new microplastic was also more effective than a cleanser that includes polyethylene microbeads, the researchers found. They also discovered that the new biodegradable particles did a better job of absorbing potentially toxic elements such as heavy metals.
“We wanted to use this as a first step to demonstrate how it’s possible to develop a new class of materials, to expand from existing material categories, and then to apply it to different applications,” Zhang says.
With a grant from Estée Lauder, the researchers are now working on further testing the microbeads as a cleanser and potentially other applications, and they plan to run a small human trial later this year. They are also gathering safety data that could be used to apply for GRAS (generally regarded as safe) classification from the U.S. Food and Drug Administration and are planning a clinical trial of foods fortified with the particles.
The researchers hope their work could help to significantly reduce the amount of microplastic released into the environment from health and beauty products.
“This is just one small part of the broader microplastics issue, but as a society we’re beginning to acknowledge the seriousness of the problem. This work offers a step forward in addressing it,” Jaklenec says. “Polymers are incredibly useful and essential in countless applications in our daily lives, but they come with downsides. This is an example of how we can reduce some of those negative aspects.”
The research was funded by the Gates Foundation and the U.S. National Science Foundation.