Novel Controlled Release Microspheric Soil Conditioner Based on the Temperature and pH Dual-Stimuli Response

Assembly of Silicate-Phenolic Network Coatings with Tunable Properties for Controlled Release of Small Molecules

Engineered coatings are pivotal for tailoring the surface properties and release profiles of materials for applications across diverse areas. However, developing robust coatings that can both encapsulate and controllably release cargo is challenging. Herein, a dynamic covalent coordination assembly strategy is used to engineer robust silicate-based coatings, termed silicate-phenolic networks (SPNs), using sodium metasilicate and phenolic ligands (tannic acid, gallic acid, pyrogallol). The coatings are pH-responsive (owing to the dynamic covalent bonding), and their hydrophobicity can be tuned upon their post-functionalization with hydrophobic gallates (propyl, octyl, lauryl gallates). The potential of the SPN coatings for the controlled release of small molecules, such as urea (a widely used fertilizer), is demonstrated-controlled release of urea in soil is achieved in response to different pHs (up to 7 days) and different hydrophobicity (up to 14 days). Furthermore, leveraging the presence of silicon (within the coating) and post-functionalization of the SPN coatings with metal ions (Fe3+, Cu2+, Zn2+) generates a multipurpose delivery system for the sustained release of micronutrient fertilizers, and silicon and metal ions, over 28 and 14 days, respectively. These SPN coatings have potential applications beyond agriculture, including nutrient delivery, separations, food packaging, and medical device fabrication.

Biodegradable Dextrin-Based Microgels for Slow Release of Dual Fertilizers for Sustainable Agriculture

In this research, we report dextrin-based biodegradable microgels (PDXE MGs) having phosphate-based cross-linking units for slow release of urea and a potential P source to improve fertilization. PDXE MGs (∼200 nm) are synthesized by cross-linking the lauroyl-functionalized dextrin chains with sodium tripolyphosphate. The developed PDXE MGs exhibit high loading (∼10%) and encapsulation efficiency (∼88%) for urea. It is observed that functionalization of PDXE MGs with lauroyl chains slows down the release of urea (90% in ∼24 days) as compared to nonfunctionalized microgels (PDX MGs) (99% in ∼17 days) in water. Further studies of the developed formulation display that Urea@PDXE MGs significantly boost maize seed germination and overall plant growth as compared to pure urea fertilizer. Moreover, analysis of maize leaves obtained from plants treated with Urea@PDXE MGs reveals 3.5 ± 0.3% nitrogen content and 90 ± 0.7 mg/g chlorophyll content. These values are significantly higher than 1.4 ± 0.6% nitrogen content and 48 ± 0.05 mg/g chlorophyll content obtained by using bare urea. Further, acid phosphatase activity in roots is reduced upon treatment with PDXE MGs and Urea@PDXE MGs, suggesting the availability of P upon degradation of PDXE MGs by the amylase enzyme in soil. These experimental results present the developed microgel-based biodegradable formulation with a slow release feature as a potential candidate to move toward sustainable agriculture practices.

Stimuli-responsive electrospun nanofibers for drug delivery, cancer therapy, wound dressing, and tissue engineering

The stimuli-responsive nanofibers prepared by electrospinning have become an ideal stimuli-responsive material due to their large specific surface area and porosity, which can respond extremely quickly to external environmental incitement. As an intelligent drug delivery platform, stimuli-responsive nanofibers can efficiently load drugs and then be stimulated by specific conditions (light, temperature, magnetic field, ultrasound, pH or ROS, etc.) to achieve slow, on-demand or targeted release, showing great potential in areas such as drug delivery, tumor therapy, wound dressing, and tissue engineering. Therefore, this paper reviews the recent trends of stimuli-responsive electrospun nanofibers as intelligent drug delivery platforms in the field of biomedicine.

Green construction and release mechanism of lignin-based double-layer coated urea

BACKGROUND

Lignin played an important role in the establishment of coated fertilizers coating material as a substitute for petrochemical raw materials. However, so far, the lignin-based coated fertilizers was limited in only the poor slow-release performance. To achieve good slow-release performance of lignin-based coated fertilizers, hydrophilic of lignin need to be resolved to establish an green and better controllable lignin-based coated fertilizers.

RESULTS

In the study, a novel green double layer coating with lignin-based polyurethane (LPU) as the inner coating and epoxy resin (EP) as the outer coating was effectively constructed for coated urea. Fourier transform infrared spectra confirmed that lignin and polycaprolactone diol successfully reacted with Hexamethylene diisocyanate. The loss weight and water contact angle (WCA, 75.6-63.6°) of the LPUs decreased with the increased lignin content. The average particle hardness of the lignin-based double-layer coated urea (LDCU) first increased from 58.1 N (lignin of 30%) to 67.0 N (lignin of 60%), but then decreased to 62.3 N (lignin of 70%). The release longevity of the coated urea was closely related to the preparation parameters of the coating material. The optimal cumulative nutrient release rate (79.4%) of LDCU was obtained (lignin of 50%, -CNO/-OH molar ratios of 1.15, EP of 35%, and coating ratio of 5%). The aggregates of hydrone on the LDCU caused the dissolution and swelling of nutrients, and then the diffusion of nutrients through the concentration gradient.

CONCLUSIONS

A though the nutrient release of the LDCUs was affected by many factors, the successful development of the LDCUs will help improve the rapid development of the coated fertilizer industry.

Hydrogels as the plant culture substrates: A review

A class of hydrophilic polymers known as "hydrogels" have extensive water content and three-dimensional crosslinked networks. Since the old period, they have been utilized as plant culture substrates to get around the drawbacks of hydroponics and soil. Numerous hydrogels, particularly polysaccharides with exceptional stability, high clarity, and low cost can be employed as plant substrates. Although numerous novel and functionalized hydrogels might assist in overcoming the drawbacks of conventional media and giving them more functions, the existing hydrogel-based plant growth substrates rarely benefit from the developments of gels in the previous few decades. Prospects include the development of new conduction techniques, the creation of potential new hydrogels, and the functionalization of the hydrogel as plant culture substrates.

A decade of developing applications exploiting the properties of polyelectrolyte multilayer capsules

Transferring the layer-by-layer (LbL) coating approach from planar surfaces to spherical templates and subsequently dissolving these templates leads to the fabrication of polyelectrolyte multilayer capsules. The versatility of the coatings of capsules and their flexibility upon bringing in virtually any material into the coatings has quickly drawn substantial attention. Here, we provide an overview of the main developments in this field, highlighting the trends in the last decade. In the beginning, various methods of encapsulation and release are discussed followed by a broad range of applications, which were developed and explored. We also outline the current trends, where the range of applications is continuing to grow, including addition of whole new and different application areas.

A Multifunctional Microspheric Soil Conditioner Based on Chitosan-Grafted Poly(acrylamide-co-acrylic acid)/Biochar

A multifunctional microspheric soil conditioner based on chitosan-grafted poly(acrylamide-co-acrylic acid)/biochar [CS-g-P(AM-co-AA)/BC] was prepared. First, the P(AM-co-AA) was synthesized and successfully grafted onto CS, and the three-dimensional network structure of microspheres was formed with N,N-methylenebis(acrylamide) as the cross-linking agent according to the inverse suspension polymerization method. Meanwhile, BC and urea were encapsulated into the body of microspheres during the polymerization. The structure of the microspheres was analyzed by Fourier transform infrared spectroscopy, polarized optical microscopy, and scanning electron microscopy, and the mechanism of adsorption of Cu²⁺ on the microspheres was investigated by X-ray photoelectron spectroscopy. Furthermore, the experimental results demonstrated the excellent water absorption and retention capabilities of microspheres, and the release rate of urea was dramatically reduced. Importantly, the introduction of BC significantly enhanced the adsorption performance of the microspheres with respect to heavy metal ions. Consequently, the multifunctional soil conditioner held promise for use in soil improvement and agricultural production.

Swelling and glyphosate-controlled release behavior of multi-responsive alginate-g-P(NIPAm-co-NDEAm)-based hydrogel

Intelligent controlled release systems (ICRS) displayed great achievement in agriculture by enhancing the utilization efficiency of agrochemicals. In this work, an intelligent graft copolymer (Alg-g-P(NIPAm-co-NDEAm)) with alginate (Alg) backbone and thermo-responsive poly(N-isopropyl acrylamide-co-N,N-diethylacrylamide) (P(NIPAm-co-NDEAm)) side chain was constructed as the matrix of ICRS through redox copolymerization, and its thermo-induced responsive property was studied. Then, the copolymer was mixed with a promising photothermal material semi-coke (SC) to form hydrogel beads (Ca-Alg-g-P(NIPAm-co-NDEAm)/SC) by ion crosslinking. The water absorbency of beads under different stimuli (pH, temperature, and light) presented outstanding responsive performance and the swelling mechanism was analyzed through coupling theory. Furthermore, the release of glyphosate (Gly) from Ca-Alg-g-P(NIPAm-co-NDEAm)/SC under environmental stimuli displayed regulatable behaviors. This multi-responsive hydrogel bead shows bright prospect in the sustainable advancement of crop production.

Materials diversity of hydrogel: Synthesis, polymerization process and soil conditioning properties in agricultural field

BACKGROUND

The cumulative influence of global warming, climate abrupt changes, growing population, topsoil erosion is becoming a threatening alarm for facing food challenges and upcoming global water issues. It ultimately affects the production of food in a water-stressed environment and slows down the production with more consumption of fertilizers by plants. The superabsorbent hydrogels (SAHs) have extensive applications in the agricultural field and proved very beneficial for plant growth and soil health. These polymeric materials are remarkably distinct from hygroscopic materials owing to their multidimensional network structure. It retains a lot of water in its 3D network and releases it slowly along with nutrients to plant in stressed environment.

AIM OF REVIEW

A soil conditioner boosts up the topology, compactness, and mechanical properties (swelling, water retention, and slow nutrient release) of soil. The superabsorbent hydrogel plays an astonishing role in preventing the loss of nutrients during the heavy flow of rainwater from the upper surface of soil because these SAHs absorb water and get swollen to keep water for longer time. The SAHs facilitate the growth of plants with limited use of water and fertilizers. Beyond, it improves the soil health and makes it fertile in horticulture and drought areas.

KEY SCIENTIFIC CONCEPT OF REVIEW

The SAHs can be synthesized through grafting and cross-linking polymerization to introduce value-added features and extended network structure. The structure of superabsorbent hydrogel entirely based on cross-linking that prompts its use in the agricultural field as a soil conditioner. The properties of a SAHs vary due to its nature of constituents, polymerization process (grafting or cross-linking), and other parameters. The use of SAHs in agricultural field comparatively enhances the swelling rate up to 60-80%, maximum water retaining, and slowly nutrient release to plants for a longer time.

Converting loess into zeolite for heavy metal polluted soil remediation based on "soil for soil-remediation" strategy

Both soil erosion and soil contamination pose critical environmental threats to the Chinese Loess Plateau (CLP). Green, efficient and feasible remediation technologies are highly demanded to meet these challenges. Herein we propose a unique "soil for soil-remediation" strategy to remediate the heavy metal polluted soil in CLP by converting loess into zeolite for the first time. With a simple template-free route, the natural loess can be converted into cancrinite (CAN) type of zeolite. A highly crystalline CAN was obtained via hydrothermal treatment at 240 ^oC for 48 h, with a precursor alkalinity of Na/(Si+Al)> 2.0. The as-synthesized CAN zeolite exhibits excellent remediation performance for Pb(II) and Cu(II) polluted soil. Plant assay experiment demonstrates that CAN can significantly restrain the uptake and accumulation of Pb(II) and Cu(II) ions in vegetables, with a high removal efficiency up to 90.7% and 81.4%, respectively. This work demonstrates a "soil for soil-remediation" strategy to utilize the natural loess for soil remediation in CLP, which paves the way for developing green and sustainable remediation eco-materials with local loess as raw materials.

Study on preparation and application of a multifunctional microspheric soil conditioner based on Arabic gum, gelatin, chitosan and β-cyclodextrin

All kinds of soil conditioners have been used to improve soil quality. The application of many traditional soil conditioners was limited by single performance. In this study, a novel multifunctional microspheric soil conditioner was prepared based on Arabic gum, gelatin, chitosan and β-cyclodextrin. Arabic gum and gelatin (AG-GL) microspheric carriers, which could load ferrous sulfate (FS), were synthesized via complex coagulation method. The AG-GL(FS) microspheres were covered by chitosan quaternary ammonium salt (CQAS) through single coagulation method. And β-cyclodextrin (β-CD) was used as the outermost shell to improve chemical stability of the soil conditioner by saturated solution method. Finally, the novel multifunctional microspheric soil conditioner AG-GL/CQAS/β-CD-FS was obtained and characterized by Fourier transform infrared spectroscopy, thermogravimetric analyzer, polarizing microscope, scanning electron microscope and particle size analyzer. The novel soil conditioner shows good nutrient slowly-releasing, water retention, heavy metal ions adsorption and antibacterial performances with the particle size of 14-17 μm and high thermal decomposition temperature, which has the potential application in improving soil quality.