Microplastics are an environmental hazard found almost everywhere on earth and are released through the decomposition of tires, clothing and plastic packaging. Another important source of microplastics are tiny beads that are added to some cleaning products, cosmetics and other beauty products.
To eliminate some of this microplastic at the source, MIT researchers have developed a class of biodegradable materials that could replace the plastic beads used in beauty products today. These polymers break down into harmless sugars and amino acids.
“One way to curb the microplastic problem is to figure out how to eliminate the existing pollution. But it’s just as important to look forward and focus on developing materials that don’t produce microplastics at all,” says Ana Jaklenec, senior researcher at MIT’s Koch Institute for Integrative Cancer Research.
These particles could also have 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, a professor at MIT and a member of the Koch Institute, are the lead authors of the article, which appears today in Natural chemical engineering. The lead author of the article 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 enriched with encapsulated iron had elevated iron levels.
However, the European Union has since classified this polymer, known as BMC, as a microplastic and included it in a ban that took effect in 2023. As a result, the Bill and Melinda Gates Foundation, which funded the original research, asked the MIT team if they could develop 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, called poly(beta-aminoester). 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 adjust 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 degradation by heat and light, but when trapped within the particles, the researchers were able to determine that the nutrients could withstand boiling water for two hours.
They also showed that even after six months of storage at high temperature and high humidity, more than half of the encapsulated vitamins remained undamaged.
To demonstrate their potential to fortify foods, researchers incorporated the particles into bouillon cubes, which are commonly consumed in many African countries. They found that when it was incorporated into the broth, the nutrients were retained even after two hours of cooking.
“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 these regions,” says Jaklenec.
In this study, researchers also tested the safety of the particles by exposing them to cultured human intestinal cells and measuring their effects on the cells. They found no damage to the cells at the doses used for food fortification.
Better cleaning
To study the particles' ability to replace the microspheres often added to cleaning products, the researchers mixed the particles with soap foam. They found that this mixture was much more effective at removing permanent marker and waterproof eyeliner from the skin than soap alone.
The researchers found that soap mixed with the new microplastics was also more effective than a cleaning product containing polyethylene microspheres. They also found that the new biodegradable particles were better at absorbing potentially toxic elements such as heavy metals.
“We wanted to use this as a first step to show how it is possible to develop a new class of materials, expand existing material categories, and then apply them to different applications,” says Zhang.
With a grant from Estée Lauder, the researchers are now working to further test the microspheres as cleaning agents and possibly other applications, and they plan to conduct a small human trial later this year. They are also collecting 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 using foods fortified with the particles.
The researchers hope their work could help significantly reduce the amount of microplastics released into the environment from health and beauty products.
“This is just a small part of the wider microplastic problem, but as a society we are beginning to recognize the seriousness of the problem. “This work represents a step forward in addressing this problem,” says Jaklenec. “Polymers are incredibly useful and indispensable in countless applications in our daily lives, but they also have disadvantages. This is an example of how we can reduce some of these negative aspects.”
The research was funded by the Gates Foundation and the US National Science Foundation.