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When agriculturalists apply herbicides to their crops, 30 to 50 percent of the substances end up in the atmosphere or soil instead of on the vegetation. Recently, a team of scholars from MIT and Singapore has created a significantly more accurate method to administer compounds to plants: tiny needles crafted from silk.
In a study published today in Nature Nanotechnology, the scholars devised a method to fabricate large quantities of these hollow silk microneedles. They utilized them to inject pesticides and nutrients into vegetation, along with monitoring their well-being.
“There’s an urgent need to enhance agricultural efficiency,” states Benedetto Marelli, the study’s lead author and an associate professor of civil and environmental engineering at MIT. “Agrochemicals are vital for sustaining our food system, but they’re also costly and pose environmental repercussions, hence the necessity for precise delivery.”
Yunteng Cao PhD ’22, presently a postdoc at Yale University, and Doyoon Kim, a prior postdoc in the Marelli lab, guided the research, which engaged a partnership with the Disruptive and Sustainable Technologies for Agricultural Precision (DiSTAP) interdisciplinary research group at the Singapore-MIT Alliance for Research and Technology (SMART).
During demonstrations, the team employed the technique to provide plants with iron to combat a condition known as chlorosis, and to incorporate vitamin B12 into tomato plants to enhance their nutritional profile. The scholars also demonstrated that the microneedles could be utilized to assess the quality of fluids entering plants and to identify when the adjacent soil contained heavy metals.
Overall, the researchers believe the microneedles could function as a novel type of plant interface for real-time health assessment and biofortification.
“These microneedles could serve as a resource for plant researchers to deepen their understanding of plant well-being and growth,” Marelli remarks. “Additionally, they can be used to increase the value of crops, making them more robust and potentially enhancing yields.”
The internal mechanisms of plants
Accessing the internal tissues of living plants necessitates that scientists navigate through the plants’ waxy exterior without inducing excessive stress. In previous work, the researchers utilized silk-based microneedles to administer agrochemicals to plants in laboratory conditions and to identify pH fluctuations in living plants. However, these initial approaches involved limited payloads, constraining their use in commercial farming.
“Microneedles were initially designed for the delivery of vaccines or other pharmaceuticals in humans,” Marelli clarifies. “Now we’ve modified it so that the technology can be applicable to plants, but initially, we were unable to deliver adequate doses of agrochemicals and nutrients to alleviate stressors or improve crop nutritional values.”
Hollow structures could amplify the volume of chemicals microneedles can provide, but Marelli notes that manufacturing those structures at scale has traditionally necessitated clean rooms and costly facilities like those within the MIT.nano building.
In this study, Cao and Kim devised a novel method of producing hollow silk microneedles by blending silk fibroin protein with a saline solution inside small, cone-shaped molds. As water evaporated from the solution, the silk solidified into the mold while the salt creates crystalline structures inside. When the salt was extracted, it left behind each needle with a hollow structure or tiny pores, determined by the salt concentration and the separation of organic and inorganic phases.
“It’s a quite straightforward fabrication process. It can be executed outside of a clean room — you could do it in your kitchen if you wished,” Kim mentions. “It doesn’t necessitate any pricey machinery.”
The researchers subsequently evaluated their microneedles’ efficiency in delivering iron to iron-deficient tomato plants, which can cause a condition known as chlorosis. Chlorosis can diminish yields, yet treating it with spray methods is ineffective and can produce environmental implications. The researchers demonstrated that their hollow microneedles could facilitate the sustained delivery of iron without harming the plants.
The researchers also proved that their microneedles could be employed to enrich crops during their growth. Traditionally, crop fortification initiatives have concentrated on minerals such as zinc or iron, with vitamins only incorporated after the food is harvested.
In each instance, the researchers manually applied the microneedles to the stalks of plants; however, Marelli envisions outfitting autonomous vehicles and other equipment already used on farms to automate and scale this process.
As part of the study, the researchers utilized microneedles to deliver vitamin B12, predominantly found in animal products, into the stalks of growing tomatoes, demonstrating that vitamin B12 was transferred into the tomato fruits prior to harvesting. The researchers propose that their method may be used to fortify more plants with the vitamin.
Co-author Daisuke Urano, a plant scientist with DiSTAP, elucidates that “through a comprehensive assessment, we demonstrated minimal adverse effects from microneedle injections in plants, with no short- or long-term negative impacts observed.”
“This innovative delivery method opens up numerous potential applications, so our goal was to achieve something nobody had attempted previously,” Marelli elaborates.
Lastly, the researchers investigated the application of their microneedles for monitoring plant health by examining tomatoes cultivated in hydroponic solutions tainted with cadmium, a toxic metal frequently found in farms near industrial and mining sites. They demonstrated that their microneedles absorbed the toxin within 15 minutes of being introduced into the tomato stalks, providing a pathway for rapid detection.
Current advanced techniques for monitoring plant vitality, such as colorimetric and hyperspectral lead analyses, can only identify issues after plant growth is already hampered. Other methods, such as sap extraction, may be too labor-intensive.
Microneedles, in contrast, could facilitate easier sap collection for ongoing chemical analysis. For instance, the researchers illustrated that they could monitor cadmium levels in tomatoes throughout an 18-hour duration.
A new platform for agriculture
The researchers believe the microneedles could complement existing farming practices such as spraying. They also note that the technology has applications extending beyond agriculture, including in biomedical engineering.
“This novel polymeric microneedle fabrication technique may also advance research in microneedle-mediated transdermal and intradermal drug delivery and health monitoring,” Cao adds.
For now, Marelli believes the microneedles offer a direction toward more accurate, sustainable agricultural practices.
“Our goal is to maximize plant growth without adversely impacting farm health or the biodiversity of nearby ecosystems,” Marelli concludes. “There shouldn’t be a trade-off between the agricultural sector and the environment. They should coexist harmoniously.”
This research was supported, in part, by the U.S. Office of Naval Research, the U.S. National Science Foundation, SMART, the National Research Foundation of Singapore, and the Office of the Prime Minister of Singapore.
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