ITHACA, N.Y. - Microplastic pollution can be found just about any place on Earth and, to the increasing concern of marine biologists, that includes oceans and waterways that are home to vulnerable plants and animals.
Engineers from Cornell University and North Carolina State University have proposed a creative solution: an army of swimming, self-propelled biomaterials called 'microcleaners' that scavenge and capture plastics so they can be decomposed by computationally-engineered microorganisms.
Their project is being funded with a $2 million grant from the National Science Foundation's Emerging Frontiers in Research and Innovation program, and combines expertise in chemistry, biology, environmental toxicology, hydrology, artificial intelligence and computer science.
Microplastics - tiny bits of sub-millimeter-sized plastic - easily pass through wastewater treatment facilities and are increasingly finding their way into oceans, among other places. They come from larger pieces of plastic debris, or are manufactured as microbeads for products such as skin cleansers and toothpastes. The environmental implications of these microplastics are not fully understood, although biologists have found evidence they alter the feeding habits of birds, fish and other wildlife.
The research team aims to design several classes of inexpensive, non-toxic microcleaners to use as micro-sized weapons against this large problem. Cornell's focus will be a class of oil droplets engineered to self-propel in water, collect microplastic particles and float to the surface, where they can be collected by barges or other large vessels. The droplets will contain chemical compounds that generate gradients in tension between the oil and water, giving them the ability to self-propel.
Interfaces of soft materials such as oil droplets are a specialty of Nicholas Abbott, the Tisch University Professor in the Smith School of Chemical and Biomolecular Engineering at Cornell, and co-principal investigator for the project.
Abbott said one of the many challenges underlying the collection of microplastics is that, in the world of microparticles, they are relatively large and diffuse very slowly in water.
"You can't wait for them to come to you to be captured," he said. "They are also present in enormous volumes of water. Our plan is to create actively propelled microsystems based on biodegradable droplets that seek out and capture the microplastic particles. Because they are self-propelled, they can search a large volume of water."
The key to making the microcleaners work is understanding the chemical makeup of the microplastics they aim to capture - another goal of the project. Microcleaners must be able to recognize a variety of plastic chemistries, some of which are altered by long exposure to sunlight or dominated by biofilms of living organisms covering the surface.
The research team will develop new analytical tools for characterizing microplastics based on liquid crystal sensors, artificial intelligence and computational design of peptides - chains of amino acids - designed to recognize and bond to the surfaces of microplastics.
The peptides will be engineered at North Carolina State, using machine-learning methods developed at Cornell by Fengqi You, the Roxanne E. and Michael J. Zak Professor in Energy Systems Engineering, and the project's co-principal investigator. You hopes to learn from the unique optical patterns produced by microplastics absorbed into novel liquid crystals designed by Abbott.
"We are taking a unique approach to develop effective deep-learning techniques for interpreting the spatial and temporal optical signals generated by microplastics adsorption at liquid crystal interfaces, thereby creating optical 'fingerprints' that indicate the species and concentration of microplastics," You said.
You will also use machine-learning techniques to support the last component of the study - engineering microbes in the form of tiny bacteria that can degrade the plastic. The microbes will carry out a biochemical process that turns microplastic into more environmentally friendly and potentially valuable materials, such as biofuels or fatty acids that can be used to produce more microcleaners.
The researchers also hope to advance the science of active microcleaner design and develop microbes for sustainable processing of plastics, other aspects of the project with potential for a variety of environmental and industrial applications.
"Conventional engineering approaches to particle capture just don't make sense on the massive scale required to impact microplastics," Abbott said. "Part of our strategy is to use products of deconstructed microplastics as the basis of microcleaners that can collect additional particles. This circular approach enables a type of a scaling up of the process that is required for an engineering solution."
North Carolina State professors Carol Hall, Orlin Velev and Nathan Crook are co-principal investigators on the project.
Helping to guide the initial research are Shaoyi Jiang, the Robert S. Langer '70 Family and Friends Professor in Cornell's Meinig School of Biomedical Engineering, and Todd Walter, professor of biological and environmental engineering in Cornell's College of Agriculture and Life Sciences.