Amphiphilicity was invoked by partially functionalizing hydrophobic PSI to form hydrophilic units, allowing for the polymer toself-assemble with a core that sequestered the model water insoluble agricultural compounds: Nile Red, Coumarin, or naphthaleneacetic acid. Upon exposure to alkaline pH, the hydrophobic succinimide portion of the polymer hydrolyzed to water-soluble aspartic acids, and the hydrophobic cargo was released from the now fully hydrophilic polymers. Furthermore, the small size of the nanoparticles and negative surface charge enhanced their internalization into plant cells, demonstrating promise as a smart nanodelivery system for delivery of agrochemicals in plant phloem. Similarly, the Sawamoto and Maynard lab collaborated to create a self-folding, amphiphilic copolymer of trehalose monomer, fluorinated monomer, and PEG monomer.Here, the fluorinated hydrophobic segment enabled the capture of a fluorinated pesticide in water. However, efficient release of the pesticide from the nanoparticles was not demonstrated, so the use of these fluorous interactions for the delivery of agrochemicals needs to be explored further.Liposomes are vesicles with inner aqueous cores surrounded by a lipid bilayer that are stable in aqueous environments, making them effective carriers of hydrophilic cargo.While liposomes have been used for agricultural application, their combination with polymers has been minimally explored, despite promising results. Karny et al. created a 100 nm polymeric liposome and tested for its ability to penetrate and distribute throughout tomato plants. They loaded the system with europium or fluorescein so the bio-distribution of liposomes could be monitored and saw translocation from the plant leaves to the roots and adjacent leaves. In cells,macetas de 5 litros the liposomes were closely associated with the nuclei, and the internalized dye released, staining the entire cell body.

Finally, the liposomes were loaded with Mg or Fe and sprayed onto Mg- and Fe-deficient tomato plants. After two weeks, the tomato plants with these treatments demonstrated significantly improved recovery compared to the commercial control formulations, demonstrating that liposomes could be promising materials for intracellular delivery of plant nutrients.Lin et al. developed a polyelectrolyte complex through electrostatic interactions between a cationic feather keratin and anionic carboxymethyl cellulose to encapsulate hydrophobic insecticide, avermectin.The hydrophobic feather keratin and avermectin assembled in the core of the complexes while the carboxymethyl cellulose polymers assembled on the exterior. Notably, the study demonstrated that as the pH of the release buffer increased, the mechanism of release transitioned from Fick diffusion to non-Fick diffusion. The authors hypothesized that this was due to the negative charge on keratin at higher pHs, resulting in repulsion from chitosan and disassembly of the complex. Polymeric materials have also exploited host-guest chemistry where hydrophobic guest molecules are sequestered in the core of a host molecule with a hydrophobic core and hydrophilic exterior. Chitosan or alginate polymeric nanoparticles functionalized with b-cyclodextrin, a host molecule, have been utilized to form inclusion complexes with hydrophobic and volatile insecticides, carvacrol and/or linalool.While these systems do not rely on self-assembly of the nanoparticles, the addition of b-cyclodextrin to the hydrophilic polymers created an amphiphilic system that captured hydrophobic actives, and the system enhanced the water solubility while decreasing the volatility of these compounds. The system demonstrated high encapsulation efficiencies while being more active against mites than the free insecticides. Micro- and nano- capsules are carriers that are typically made with a hydrophilic, water permeating polymeric shell and lipophilic core which carries hydrophobic cargo.

Capsules with liquid cores are typically created by templating emulsions and traditionally have used toxic emulsifiers and organic solvents.For a more sustainable and green approach, Tang et al. used Pickering emulsions to create polydopamine microcapsules for the encapsulation of an essential oil, turpentine, and pesticide, 4-chloro-2-methylphenoxyacetic acid .Emulsions of turpentine and 2,4-D were stabilized by solid cinnamoyl chloride-modified cellulose nanocrystals and acted as a template to produce the PDA capsules. Both turpentine and 2,4-D were slowly released from the capsule as compared to the free pesticide controls. Another intriguing example of a capsule system utilized proteinoid polymers, produced by the step-growth polymerization of natural and unnatural amino acids, that self-assembled into a nanosized hollow nanoparticle to balance the hydrophobic and hydrophilic components within the proteinoid backbone.This system was implemented for the encapsulation of auxin plant hormones and was externally modified with dodecyl aldehyde or Cyanine3 dye to increase the particle hydrophobicity for better foliar application or allow tracking of the nanoparticles within a plant’s vascular system, respectively. Interestingly, a proteinoid backbone contained a conjugated amino acid herbicide was also tested and found to be toxic to plants without any internalized actives. Previous studies demonstrated that the amino acid is only active in its monomeric form, so the authors hypothesized that the free amino acid herbicide was releasing from the peptide chain via biodegradation. Although this idea was not further explored in this study, other conjugated actives have been explored in agricultural settings. In addition to formulations based on non-covalent interactions, agrochemicals have also benefited from chemically binding to small molecules or polymers which further optimize formulation physicochemical properties, selectivity, and biological activity . Amino acid or glucose conjugation of fungicides and insecticides have improved their plant phloem mobility,lipid-like amphiphilic-conjugates of agrochemicals have induced self-assembling behavior,and hydrophobic moiety conjugates of herbicides have enhanced their water and soil stability.

While some of these conjugation strategies are irreversible, others form reversible linkages which eventually convert to an active parent ingredient , thus improving their selectivity.Traditionally, propesticides are inactive and require a transformation event within the target organism or surrounding environment to release an active chemical. Studies have focused on the chemical linkage of a limited set of agrochemicals containing carboxylic acid, amine, or alcohol functional groups. These groups provide scaffolds to form hydrolytically- or enzymatically-reversible ester or amide linkages. While some of the systems discussed in this section exist in forms discussed in the previous section , these examples are specifically highlighted here for their chemical linkage and cleavage strategies. Agrochemicals with carboxylic acid moieties are hydrophilic in nature and are therefore susceptible to leaching and contaminating groundwater. To prevent these adverse effects, herbicides and plant growth hormones with carboxyl functional groups have been modified with polymers through ester or amide linkages. The herbicides 2-methyl-4-chlorophenoxyacetic acid or 2,4-D have been applied as an anionic initiator for ring opening polymerizations to form ester-linked, end-functionalized degradable polymers.Compared to the free herbicide, these polymers released lower concentrations of the herbicide over time while still effectively preventing weed growth. Additionally, the herbicide-polymer conjugate was incorporated into a biodegradable mulch film, demonstrating the potential functional versatility of polymeric formulations. Through amide or ester linkages, 2,4-D has also been incorporated as a pendant group of a degradable polymeric backbone. One study demonstrated pH-dependent hydrolysis of a combined ester-amide linkage with the herbicide releasing faster in alkaline versus acidic conditions.Another study used a cysteamine- modified 2,4-D, creating an amide linkage and free thiol that could react with PDA nanoparticles via Michael addition.This study compared the release of conjugated 2,4-D and the release of non-conjugated 2,4- D from PDA nanoparticles. They observed a significant difference in the release kinetics, where, over 190 hours, only 10 % of the amide conjugated herbicide released in various pH solutions as opposed to 30-60 % release of 2,4-D when only physically encapsulated. This direct comparison shows release kinetics can be tuned by conjugated agrochemicals. However, the conjugated nanoparticles did adhere less to leaves than their physical encapsulation counterparts, indicating that when some of the PDA catechols are substituted, their adhesive properties diminish.

While these examples focus on the hydrolytic response of the herbicide release and polymer degradation, other reports have demonstrated that herbicide conjugates with amide and ester linkages can also be cleaved when exposed to photochemical or biochemical stimuli. Yin and Yi reported the grafting of 2,4-D to PEG through an ester-linkage to a photo-labile onitrobenzyl group.Due to the amphiphilic nature of the hydrophilic PEG polymer with hydrophobic 2,4-D-modified end group, micelle formation in aqueous conditions was reported. The micelles were photo-responsive, demonstrating no herbicidal release without light irradiation and quantitative release over nine days with solar simulated irradiation. These types of systems also have the potential to increase the water solubility of the hydrophobic active ingredients they carry. Enzymatically-responsive amide-linked systems have also been prepared with gibberellin, plant growth regulator,macetas cultivo conjugated to amino groups on the biopolymer.118 While the conjugate slowly released gibberellin when subjected to hydrolysis, the response was much faster when subjected to amidase or amidohydrolases, enzymes abundant in plants. Moreover, the conjugate improved the solubility of gibberellin and protected it against thermal- and photo-degradation.Similarly, agrochemicals with hydroxyl groups have been conjugated to polymers through ester linkages. In particular, plant growth enhancing brass inosteroid synthetic analogues have been modified with carboxylic acid-containing PEG micelles,chitosan, hyaluronic acid and silk fibroin.Due to the hydrophobicity and quick metabolism in plants of brassinosteroids, their application in agriculture has been limited. However, when modified with PEG, the amphiphilic conjugate forms a micelle in aqueous solutions and establishes controlled release and extendedstabilization of the steroids. Moreover, bio-assays of radish seeds with the conjugate demonstrated increased biomass compared to the unconjugated control. The other polymeric conjugates with biopolymers, silk fibroin, chitosan, and hyaluronic acid, exhibited pH and/or temperature controlled release of the steroids in aqueous solutions. These systems show the modularity available in conjugate systems; various polymers can be utilized with the same agrochemicals as long as they contain a compatible functional groupAgrochemicals with amino groups have also been chemically grafted to carboxyl groups on polymers, forming amide linkages. Emamectin benzoate, a photochemically-labile insecticide with a free amine, was transformed into an acrylamide monomer and co-polymerized with butyl acrylate and methyl methacrylate monomers to form nanoparticles.The nanoparticles dramatically improved the stability of emamectin benzoate with approximately 30 % decomposed after three days under simulated sunlight, compared to 90 % decomposition of the control pesticide.

Additionally, the particles demonstrated enhanced toxicity against Helicorvapa armigera pests compared to free emamectin benzoate. Here, reversibility was not demonstrated, so it is unclear if the conjugate itself is active or if it is a proinsecticide. Another amide conjugate was synthesized through the amino group of kasugamycin, an antibiotic used for plant disease control, and the carboxyls of the biopolymer pectin.The conjugate was stable to UV irradiation and a range of pH and temperatures, but released upon incubation with a pathogenic bacteria that causes melon bacterial angular leaf spot, Pseudomonas syringae pv. lachrymans, due to its enzymatic response.Hydrogels are three-dimensional polymeric networks that hold large quantities of water and have been utilized in a myriad of applications due to their tunable properties. Natural or synthetic polymers can form these scaffolds where synthetic polymers offer more control over gel properties and less batch-to-batch variability than natural polymers.Depending on the functionality of the polymers and implemented cross-linking strategy, synthetic hydrogels have been used for diverse applications such as tissue engineering,drug-delivery,and soil amendments.In particular, they are attractive scaffolds for the encapsulation, stabilization, and controlled-release of water-soluble bio-macromolecules like proteins due to their porous structure and water content. The encapsulation of proteins can occur during hydrogel formation11 or via diffusion into the hydrogel’s pores post-synthesis.The latter method allows for the synthesis of bulk hydrogels, which can later be employed to immobilize a scope of proteins, including enzymes that are used for various industrial applications. In this work, trehalose hydrogels were prepared for the encapsulation of enzymes and subsequent protection to thermal stress, which is known to inactivate proteins often via changes in protein conformation and formation of insoluble aggregates.Trehalose is a disaccharide formed by a,a-1,1-linked glucopyranose units and is upregulated by organisms during prolonged terms of desiccation.The accumulation of trehalose protects proteins,allowing the survival of these organisms in extreme environments including high temperatures. We have previously developed trehalose-functionalized materials for thermostabilization of proteins,including a trehalose hydrogel.However, the yield , scalability, and sustainability of the hydrogel synthesis needed significant improvement to be useful. Herein, we report a scalable trehalose hydrogel synthesis with high yields that employs more environmentally benign solvents. Additionally, the ability of the gel to thermostabilize three major enzymes utilized in animal feed, as well as a relevant enzyme release rate, is described, supporting its potential usefulness for the livestock industry.We reported a straight-forward gel synthesis by first modifying trehalose via Williamson etherification using 4-vinylbenzyl chloride and sodium hydroxide in dimethylsulfoxide to produce mono- or multi-functional styrenyl-trehalose.After a precipitation step to remove DMSO and other impurities and to isolate the crude reaction mixture, the mixture was dried to a yellow powder prior to polymerization in water.