Trans­form­ing flies into degrad­able plastics

Ima­gine using insects as a source of chem­ic­als to make plastics that can bio­de­grade later — with the help of that very same type of bug. That concept is closer to real­ity than you might expect. Research­ers will describe their pro­gress to date, includ­ing isol­a­tion and puri­fic­a­tion of insect-derived chem­ic­als and their con­ver­sion into func­tion­al bioplastics.

“For 20 years, my group has been devel­op­ing meth­ods to trans­form nat­ur­al products — such as gluc­ose obtained from sug­ar cane or trees — into degrad­able, digest­ible poly­mers that don’t per­sist in the envir­on­ment,” says Kar­en Wooley, Ph.D., the project’s prin­cip­al invest­ig­at­or. ​“But those nat­ur­al products are har­ves­ted from resources that are also used for food, fuel, con­struc­tion and transportation.”

So Wooley began search­ing for altern­at­ive sources that wouldn’t have these com­pet­ing applic­a­tions. Her col­league Jef­fery Tomber­lin, Ph.D., sug­ges­ted she could use waste products left over from farm­ing black sol­dier flies, an expand­ing industry that he has been help­ing to develop.

The lar­vae of these flies con­tain many pro­teins and oth­er nutri­tious com­pounds, so the imma­ture insects are increas­ingly being raised for anim­al feed and to con­sume wastes. How­ever, the adults have a short life span after their breed­ing days are over and are then dis­carded. At Tomberlin’s sug­ges­tion, those adult car­casses became the new start­ing mater­i­al for Wooley’s team. ​“We’re tak­ing some­thing that’s quite lit­er­ally garbage and mak­ing some­thing use­ful out of it,” says Cas­sidy Tib­betts, a gradu­ate stu­dent work­ing on the pro­ject in Wooley’s lab at Texas A&M University.

When Tib­betts examined the dead flies, she determ­ined that chitin is a major com­pon­ent. This non­tox­ic, bio­de­grad­able, sug­ar-based poly­mer strengthens the shell, or exo­skel­et­on, of insects and crus­ta­ceans. Man­u­fac­tur­ers already extract chitin from shrimp and crab shells for vari­ous applic­a­tions, and Tib­betts has been apply­ing sim­il­ar tech­niques using eth­an­ol rinses, acid­ic demin­er­al­iz­a­tion, basic depro­tein­iz­a­tion and bleach decol­or­iz­a­tion to extract and puri­fy it from the insect car­casses. She says her fly-sourced chitin powder is prob­ably purer, since it lacks the yel­low­ish col­or and clumpy tex­ture of the tra­di­tion­al product. She also notes that obtain­ing chitin from flies could avoid pos­sible con­cerns over some sea­food aller­gies. Some oth­er research­ers isol­ate chitin or pro­teins from fly lar­vae, but Wooley says her team is the first that she knows of to use chitin from dis­carded adult flies, which — unlike the lar­vae — aren’t used for feed.

While Tib­betts con­tin­ues to refine her extrac­tion tech­niques, Hong­ming Guo, anoth­er gradu­ate stu­dent in Wooley’s lab, has been con­vert­ing the pur­i­fied fly chitin into a sim­il­ar poly­mer known as chitosan. He does this by strip­ping off chitin’s acet­yl groups. That exposes chem­ic­ally react­ive amino groups that can be func­tion­al­ized and then cross­linked. These steps trans­form chitosan into use­ful bioplastics such as super­ab­sorb­ent hydro­gels, which are 3D poly­mer net­works that absorb water.

Guo has pro­duced a hydro­gel that can absorb 47 times its weight in water in just one minute. This product could poten­tially be used in cro­p­land soil to cap­ture flood­wa­ter and then slowly release mois­ture dur­ing sub­sequent droughts, Wooley says. ​“Here in Texas, we’re con­stantly either in a flood or drought situ­ation,” she explains, ​“so I’ve been try­ing to think of how we can make a super­ab­sorb­ent hydro­gel that could address this.” And because the hydro­gel is bio­de­grad­able, she says it should gradu­ally release its molecu­lar com­pon­ents as nutri­ents for crops.

This sum­mer, the team is 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, which are tra­di­tion­ally made from pet­ro­chem­ic­als. Black sol­dier flies also con­tain many oth­er use­ful com­pounds that the group plans to use as start­ing mater­i­als, includ­ing pro­teins, DNA, fatty acids, lip­ids and vitamins.

The products made from these chem­ic­al build­ing blocks are inten­ded to degrade or digest when they’re dis­carded, so they won’t con­trib­ute to the cur­rent plastic pol­lu­tion prob­lem. Wooley’s vis­ion for that pro­cess would align it with the sus­tain­able, cir­cu­lar eco­nomy concept: ​“Ulti­mately, we’d like the insects to eat the waste plastic as their food source, and then we would har­vest them again and col­lect their com­pon­ents to make new plastics,” she says. ​“So the insects would not only be the source, but they would also then con­sume the dis­carded plastics.”