Millennia has passed since silk was discovered and harvested from silkworm cocoons. However, scientists continue to find new uses for this amazing material. Now researchers say it could help tackle a growing environmental and health concern: microplastics, the minuscule plastic fragments that have been found everywhere from mountaintops to the seafloor–and even in the human bloodstream.
Most environmental microplastics are formed when larger items break down. According to the European Chemicals Agency, a small but significant portion of polluting particles are intentionally added to products. These microcapsules protect and slowly release active ingredients in products like cosmetics and agricultural sprays.
For a study published in Small, researchers at the Massachusetts Institute of Technology and chemical corporation BASF developed a silk-based, biodegradable alternative to these capsules. This research is crucial for companies facing tighter regulations on the deliberate use of microplastics.
Finding substitute material for intentionally added microplastics is the only way to control microplastic pollution, according to Denise Mitrano (ETH Zurich environmental analytical chemist), who was not involved with the study.
Silk, which is non-toxic, can withstand processing and can be obtained from low-quality fibers discarded by the textile sector, according to M.I.T. Benedetto Marelli, an engineer and co-author of the study. Marelli states that researchers have suggested other natural compounds as a replacement for intentionally added microplastics. However, these “cannot check all the boxes at once, like we were able with silk.”
Researchers retrofitted existing manufacturing equipment in order to create microcapsules with silk protein fibroin. This allowed them to control how the long protein chains of silk fold and stick together, “tuning” the microcapsules so that they dissolve and release active ingredients at different rates.
Silk-based microcapsules must be commercially competitive. Marelli states that they must perform at the same level as nonbiodegradable counterparts. Some herbicides are sprayed slowly to kill weeds, but not harm food crops. The silk-based microcapsule spray caused less damage to corn plants than a commercial product when it was tested for six days.
Replacing nonbiodegradable microcapsules using silk might not work for every case but it looks promising compared to other alternatives BASF has examined, says Pierre-Eric Millard (a microencapsulation scientist at BASF). He says that products made with silk-based microcapsules might be commercially available within a few years, if BASF implements them.
The researchers will next attempt to encapsulate active ingredients that may require a different manufacturing process, such as those that must be kept in liquid or gas forms.