Bioplastic from black soldier flies? US researchers pioneer circular economy novelty

15 Aug 2023 --- US researchers are developing a technique to build bioplastic from black soldier flies. The flies contain chitin, a non-toxic, biodegradable, sugar-based polymer that can be purified and converted into a similar polymer called chitosan.

Chitosan can be transformed into bioplastics such as super absorbent hydrogels, which are 3D polymer networks that absorb water. The findings were presented at the ongoing American Chemical Society fall meeting.

“Our dream is to set up a cyclical system where we can harvest building blocks from black soldier flies and transform them into functional high-end plastic materials,” says Karen Wooley, the project’s principal investigator at Texas A&M University, US.

“When those plastic materials are discarded in the environment, they can be broken down by ingestion by the black soldier flies or other species. In the case of the black soldier flies, we could collect their carcasses again and harvest new building blocks, from which we can make new plastic materials in a complete circularity.”

Addressing plastic pollution
The team is also starting a project to break down chitin into its monomeric glucosamines. These small sugar molecules will then be used to make bioplastics such as polycarbonates or polyurethanes, traditionally made from petrochemicals.

Black soldier flies are a good source of chemicals to make bioplastics (Image credit: Cassidy Tibbetts).Black soldier flies contain many other valuable compounds that the group plans to use as starting materials, including proteins, DNA, fatty acids, lipids and vitamins.

“The primary implications from our findings are that the vast array of biomass sources is expanding. For many years, people thought they had to use sugar cane or cellulose from trees and harvest materials from that to build synthetic materials. There’s a lot of work on algae. Now we’re showing that even flies can be used as a source from which plastics can be derived,” Wooley stresses. 

“The thing about building those plastics up is we’re building in linkages that we can break back down. So these materials are meant to be degradable if they’re lost in the environment and digestible. If humans collect and sort them for processing, they can be recycled. There are many vast implications from the sourcing to the end application that bring in things like sustainability and addressing plastic pollution.”

“Degradable, digestible polymers”
Wooley details that the farming and harvesting of black soldier flies is particularly easy as well as cost-efficient and can be applied across the world with minimal resources. The adults are required for reproduction. However, they have a very short lifespan as they only live about a week to mate and lay eggs, and then they’re essentially wasted.

“For 20 years, my group has been developing methods to transform natural products – such as glucose obtained from sugarcane or trees – into degradable, digestible polymers that don’t persist in the environment,” she says.

“But those natural products are harvested from resources that are also used for food, fuel, construction and transportation.”

With the black soldier flies, Wooley is attempting to work with an alternative source without competing applications.

Development process
The researchers have, so far, isolated chitin in about 6% yield using a four-step process. The hydrogel developed by Wooley’s team is capable of holding water weight 47 times its mass.

“The first step is we take the whole fly, rinse and clean it, and then dry it and grind it to give us a powder. This powder is then treated with acid for demineralization, followed by a deproteinization, using a base, and finally a decolorization using bleach to give us this white chitin product,” says Cassidy Tibbetts, a graduate student working on the project in Wooley’s lab.

While Tibbetts continues refining her extraction techniques, Hongming Guo, another graduate student in Wooley’s lab, has been converting the purified fly chitin into a similar polymer called chitosan. 

He does this by stripping off chitin’s acetyl groups. That exposes chemically reactive amino groups that can be functionalized and then cross-linked. 

“Those super absorbent hydrogels are biodegradable and they can capture water fast in about one minute and 47 times their mass. They have a high capacity and fast recovery,” share the researchers.

Flies for circularity
The researchers are looking into feeding the insects plastic waste as a food source, harvesting the insects and collecting their components to make new plastics. “The insects would not only be the source, but they would also then consume the discarded plastics,” says Wooley.

Tibbetts adds that the use of the adult flies, in particular, is helping to close the circular economy for the black soldier fly.

“We focus on procedures that are scalable because the black soldier fly adult waste exists in a significant quantity, and we want to be able to find a process that is able to make use of that in large quantities. Also, the chitin yield is currently only at 6% and probably maximum at 8-10%, based on previous literature for what is in the adult flies.”

“The applications for chitin, however, are endless because it can be transformed into chitosan, both of which have massive uses in almost every industry, from medical, cosmetic and plastics. We’re currently focusing on the super absorbent hydrogels, but the applications are endless,” Tibbetts concludes.

By Radhika Sikaria