In situ forming dialdehyde xanthan gum-gelatin Schiff-base hydrogels as potent controlled release fertilizers

Crosslinking of gelatin Schiff base hydrogels with different structural dialdehyde polysaccharides as novel crosslinkers: Characterization and performance comparison

Few studies have been conducted on the relationship between the crosslinking ability of dialdehyde polysaccharides (DPs) with different structures and the structure and properties of hydrogels. Herein, the effects of dialdehyde sodium alginate (DSA), dialdehyde guar gum (DGG), and dialdehyde dextran (DDE) as crosslinking agents for gelatin (GE)-based hydrogels were comparatively studied. First, the structure and aldehyde content of DPs were evaluated. Subsequently, the structure, crosslinking degree, and physicochemical properties of GE/DP hydrogels were characterized. Compared with pure GE hydrogels, GE/DP hydrogels had higher thermal stability and mechanical properties. Moreover, the aldehyde content of DPs was ordered as follows: DSA < DGG < DDE. The higher crosslinking degree of the hydrogels formed by DPs with a higher aldehyde content resulted in smaller hydrogel pores, higher mechanical strength, and a lower equilibrium swelling rate. These observations provide a theoretical basis for selecting crosslinking candidates for hydrogel-specific applications.

Chitosan xerogel embedded with green synthesized cerium oxide nanoparticle: An effective controlled release fertilizer for improved cabbage growth

With the growing awareness on the adverse effects of conventional fertilizers; the use of sustainable and controlled release fertilizers has garnered much significance. In the present study, we report the synthesis of chitosan-benzaldehyde Schiff base xerogel incorporated with green synthesized cerium oxide nanoparticle using Psidium guajava leaves extract as a sustainable fertilizer. Spherical CeO2 NPs having an average particle size of 15.3 nm and zeta potential of - 39.9 mV was obtained. The urea-loaded nanocomposite xerogel (CsB@U/CeO2) was examined for cabbage growth. The water retention capacity extended for >2 weeks. A controlled release profile for urea was accomplished from CsB@U/CeO2 for a period extending for 30 days. The kinetics assay suggested that presence of CeO2 NPs asserted a greater role in urea-controlled release from the CsB@U/CeO2 nanocomposite hydrogel owing to polymer relaxation. The growth parameters of cabbages such as head height, diameter, fresh head weight, head circumference was enhanced in plants fertilized by CsB@U/CeO2 as compared to urea. Furthermore, the phenolic content, free radical scavenging activity, protein content, sugar and flavonoid content were also found higher in CsB@U/CeO2 fertilized plants. This study puts forth CsB@U/CeO2 xerogel can be potentially harnessed as an alternative to urea in sustainable agriculture.

An update review on biopolymer Xanthan gum: Properties, modifications, nanoagrochemicals, and its versatile applications in sustainable agriculture

During the development of green agriculture and pesticide use, "reducing pesticides use and improving control efficiency" is imperative. To date, new pesticide formulations created by nanotechnology can be expected to overcome the difficulties that cannot be solved by the traditional pesticide processes and make pesticide formulations close to the needs of green agricultural production. As natural polysaccharides, Xanthan gum (XG) charactered by a repeated units and side chain of d-glucose, d-mannose, and d-glucuronic acid, and thereby having the unprecedented features in response to wide practice in various fields. This review introduces the properties of the natural polymer XG and its current status of application in agriculture, focusing on the pesticide adjuvant and preparation of novel pesticide and fertilizer delivery systems (such as core-shell and hydrogel), and combined with the applications in mulch film and soil engineering. Furthermore, the properties of Xantho-oligosaccharides suitable for agriculture were discussed. Finally, the potential of XG for the creation of nanopesticides and its future prospects are highlighted. Taken together, XG's excellent performance endows it with a wide range of applications in the agriculture field, and result in strong stimulating the sustainable development of agriculture and evolution of agricultural industry.

A biodegradable multifunctional pectin-montmorillonite fertilizer coating: Controlled-release, water-retention and soil-cementation

Coated fertilizers have been widely used to improve fertility in barren land. However, improving soil structure and water-retention capacity is also essential for arid and semi-arid areas with sandy soils to promote crop growth. Most currently available coated fertilizers rarely meet these requirements, limiting their application scope. Therefore, this study "tailored" pectin-montmorillonite (PM) multifunctional coatings for arid areas, featuring intercalation reactions and nanoscale entanglement between pectin and montmorillonite via hydrogen bonding and electrostatic and van der Waals forces. Notably, PM coatings have demonstrated an effective "relay" model of action. First, the PM-50 coating could act as a "shield" to protect urea pills, increasing the mechanical strength (82.12 %). Second, this coating prolonged the release longevity of urea (<0.5 h to 15 days). Further, the remaining coating performed a water-retention function. Subsequently, the degraded coating improved the soil properties. Thus, this coating facilitated the growth of wheat seedlings in a simulated arid environment. Moreover, the cytotoxicity test, life cycle assessment, and soil biodegradation experiment showed that the PM coating exhibited minimal environmental impact. Overall, the "relay" model of PM coating overcomes the application limitations of traditional coated fertilizers and provides a sustainable strategy for developing coating materials in soil degradation areas.

Facile preparation of interpenetrating network hydrogel adsorbent from starch- chitosan for effective removal of methylene blue in water

Hydrogels based on biopolymers have attracted considerable interest in the last decades. Herein, an interpenetrating network hydrogel (IPN-Gel) adsorbent from starch-chitosan was fabricated facilely in one-pot through tandem Schiff base reaction and photopolymerization. First, aldehyde starch (DAS) was synthesized by the reaction of soluble starch with sodium periodate. Afterward, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), polyethylene glycol dimethacrylate (PEGDMA), photoinitiator, chitosan and DAS were dissolved in water to obtain a clear solution. Schiff base reaction between chitosan and DAS took place quickly to form the first network, and then photopolymerization of AM, AMPS, and PEGDMA occurred under ultraviolet radiation to form the second network. The preparation conditions of the as-prepared IPN-Gel were optimized with two indexes of gel mass fraction and swelling ratio. Its swelling behavior with pH and temperature change was explored. Finally, its adsorption performance was characterized with methylene blue (MB) as a model contaminant. The maximum adsorption capacity of IPN-Gel can reach 2039 mg·g-1 at pH =10. Its adsorption performance accords with Langmuir isothermal model and pseudo-second-order kinetic model and it was mainly controlled by chemisorption. This strategy is expected to found broad application prospects in the preparation of hydrogel adsorbents.

Preparation and characterization of starch carbamate modified natural sodium alginate composite hydrogel blend formulation and its application for slow-release fertilizer

The exploration of environmentally friendly slow-release fertilizer (SRF) based on natural bio-polymers is of great importance in the development of modern agriculture and horticulture. Herein, a novel starch carbamate (SC) modified sodium alginate (SA) hydrogel (SC/SAH) was prepared utilizing as-synthesized SC and natural SA through the cationic ions crosslinking method and ultimately the corresponding slow-release fertilizer (SC/SAH-SRF) was successfully developed by immersing the dried SC/SAH matrix into saturated urea solution. Due to the low gelation temperature and high viscosity of the synthesized SC, the formed SC/SAH exhibits significantly enhanced properties including excellent water absorbency up to 8.02 g/g with considerable repeatability, abundant pore structure and high hydrophilicity compared with the neat SAH and natural starch based hydrogel (NS/SAH). Accordingly, the SC/SAH leads to higher urea loading amount ∼ 1.28 g/g. Importantly, the resultant SC/SAH-SRF also shows superior slow-release performance, yielding a cumulative urea release of only 61.6 % within 10 h and almost completely release >16 h in water, what's more, only 58.5 % of the urea releases within 25 days and exceeding 50 days for complete release in soil column assays. The slow-release of urea from SC/SAH-SRF well complies for the first-order kinetics and accomplishes via a non-Fickian diffusion process. Moreover, the pot experiment demonstrates that the SC/SAH-SRF has higher growth promotion role for the maize seedlings than those of others. Consequently, this work provides a novel strategy for preparing environmentally friendly SRF by blending modified starch and hydrogel.

Characterization of gelatin-oxidized riclin cryogels and their applications as reusable ice cubes in shrimp preservation

Traditional ice is usually employed to preserve food freshness and extend shelf life. However, ice cannot bear repeated freeze - thaw cycles during the transportation and retailing process, resulting in microbial cross-contamination and spoilage of foods. Herein, succinoglycan riclin was oxidated (RO) and crosslinked with gelatin (Ge), the Ge-RO cryogels were prepared via Schiff base reaction and three freeze - thaw cycles. The Ge-RO cryogels showed improved storage modulus (G') and thermal stability compared with pure gelatin hydrogel. The polymer framework of Ge-RO gels exhibited stable properties against ice crystals destructions during nine freeze - thaw treatments. During the storage and repeated freeze - thaw treatments of shrimps, Ge-RO cryogels exhibited a remarkable preservation effect on shrimps, and their freshness was evaluated using an electronic nose technique equipped with ten sensors. The results demonstrated that the shrimp muscle preserved in ice generated off-odors and resulted in high sensor responses. The sensor responses were reduced sharply of shrimps preserved in cryogels. Moreover, 1H NMR-based metabolomics analysis revealed that shrimps in Ge-RO cryogels group reversed the metabolic perturbations compared with the traditional ice group, the metabolic pathways were related to energy metabolism, nucleotide metabolism, and amino acid metabolism, which provide new clues to the freshness of shrimps. Furthermore, RO exhibited superior antimicrobial activity against E. coli and S. aureus microorganisms. Thus, the crosslinked cryogels are potentially applicable to food preservation, offering sustainable and reusable solutions against traditional ice.

Highly efficient removal of tannic acid from wastewater using biomimetic porous materials

To effectively remove tannic acid (TA) from wastewater, using green and natural materials has attracted increasing attention. Inspired by Galla Chinensis (GC) with high content of TA, this study synthesized a biomimetic porous adsorbent to mimic the GC structure using dialdehyde tapioca starch (DTS) and gelatin (GL). The TA adsorption performance and mechanism of synthetic porous material were investigated. Results revealed that the porous material exhibited a maximum TA adsorption capacity of 1072.01 mg/g, along with a high removal rate of 95.16% under the conditions of a DTS-GL mass ratio of 1:1, DTS aldehyde content of 48.16%, a solid content of 5%, and a pH of 2 at 25 °C. The adsorption of TA by DTS was not affected by water-soluble cationic and anion. The adsorption kinetics of TA on the porous material followed the pseudo-second-order model, and this Langmuir adsorption model (R2 = 0.9954) which were well described the adsorption of TA by the material, indicating that the adsorption primarily occurred in a monolayer. FTIR, XRD, DSC, TG, XPS, and SEM-EDS were employed to characterize the structure characteristics of the porous material. The cross-linking between DTS and GL by Schiff base reaction imparted a chemical structure could absorb TA by hydrogen bonding. The TA desorption rates of in 30% acetone and 40% ethanol solutions were 88.76% and 91.03%, respectively. The porous material prepared by the GC-inspired approach holds promise as an ideal choice for loading polyphenolic compounds and provides a new perspective for the design and application of bioinspired engineering materials.

Effect of sodium alginate block type on the physicochemical properties and curcumin release behavior of quaternized chitosan-oxidized sodium alginate Schiff base hydrogels

Controlling bioactive ingredients release by modulating the 3D network structure of cross-linked hydrogels is important for functional food development. Hereby, oxidized sodium alginate (OSA) with varying aldehyde contents was formed by periodate oxidation of sodium alginate (SA) with different β-d-mannuronic acid (M) and α-l-guluronic acid (G) ratios (M/G = 1:2, 1:1, and 2:1) and its structure was characterized. Moreover, hydrogels were prepared via Schiff base and electrostatic interactions between quaternized chitosan (QCS) and OSA. The properties of hydrogels such as microstructure, thermal stability, swelling and controlled release were investigated. The results showed that OSA with M/G = 1:2 had the highest content of aldehyde groups, and the hydrogel formed by it and QCS had higher thermal stability and a denser network structure with the lowest equilibrium swelling rate, which could better control the release of curcumin. Additionally, it had good self-healing and can recover rapidly after the rupture of its network structure.

Design and manufacture of new hybrid hydrogel and superabsorbent polymer for controlled release of fulvic acid based on grafted xanthan gum/gelatin using electron irradiation and its use in fodder corn cultivation

A humic acid-gelatin (HA-Gel) hydrogel, a gallic acid-xanthan gum (GA-XG) hydrogel, a HA-Gel/GA-XG hydrogel, and superabsorbent polymer (SAP) of HA-Gel/GA-XG/polyacrylamide (PAM) hydrogel were synthesized using electron beam irradiation method. The capability of synthesized hydrogels in loading and controlled release of fulvic acid (FA) was studied. The chemical and physical structure of sorbents was confirmed by various analyses. The effect of irradiation dose on mechanical properties, gel percentage, swelling, and absorbency under load (AUL) of the sorbents was investigated. By changing the hydrogel structures into the SAP form, its swelling capacity was increased from 37 to 320 g/g. Both hybrid hydrogel and SAP were reusable for up to 7 cycles. The maximum fertilizer loading capacities for SAP and hybrid hydrogel were 402.1 and, 175.5 mg g-1, respectively. In comparison to hydrogels, the SAP showed a slower FA-release performance. Thus, in soil media, 86 % of FA was released in 15-20 days from the hybrid hydrogel while with the SAP, 81 % of FA was released in 30-35 days. The significant improvement in the growth of fodder corn treated with FA-loaded SAP in the greenhouse media in comparison to the control groups showed the effective performance of the designed SAP, favoring its practical applications.

Rhizobial oxidized 3-hydroxylbutanoyl glycan-based gelatin hydrogels with enhanced physiochemical properties for pH-responsive drug delivery

Rhizobial exopolysaccharide (EPS) is an acidic polysaccharide involved in nitrogen fixation-related signal transduction in the rhizosphere, serving as a structural support for biofilms, and protecting against various external environmental stresses. Rhizobial EPS as a hydrogel biomaterial was used for a pH-responsive drug delivery system combing with gelatins. Pure gelatin (GA) hydrogels have limited practical applications due to their poor mechanical strength and poor thermal stability. We developed new GA hydrogels using oxidized 3-hydroxylbutanoyl glycan (OHbG) as a polymer cross-linking agent to overcome these limitations. OHbG was synthesized from sodium periodate oxidation of 3-hydroxylbutanoyl glycan directly isolated from Rhizobium leguminosarum bv. viciae VF39. The newly fabricated OHbG/GA hydrogels exhibited 21-fold higher compressive stress and 4.7-fold higher storage modulus (G') than GA at the same strain. This result suggested that OHbG provided mechanical improvement. In addition, these OHbG/GA hydrogels showed effective pH-controlled drug release for 5-fluorouracil, self-healable, and self-antioxidant capacity by uronic acids of OHbG. Cell viability tests using HEK-293 cells in vitro also showed that the OHbG/GA hydrogels were non-toxic. This suggests that the new OHbG/GA hydrogels can be used as a potentially novel biomaterial for drug delivery based on its self-healing ability, antioxidant capacity, and pH-responsive drug delivery.

In situ forming of PEG-NH2/dialdehyde starch Schiff-base hydrogels and their application in slow-release urea

In this study, a biodegradable Schiff-base hydrogel urea, possessing substantial water retention and certain slow-release ability was designed and synthesized. Firstly, dialdehyde starch (DAS) and amine-terminated polyethylene glycol (PEG-(NH2)2) were synthesized using potato starch and polyethylene glycol. Then, a novel Schiff-base hydrogel (SH) was prepared through the in-situ reaction between the aldehyde group of DAS and the amino group of PEG-(NH2)2. Three SH based slow-release urea, designated as SHU1, SHU2, and SHU3 and distinguished by varying urea content, were obtained using SH as the substrate. Several characterizations and tests were conducted to determine the structure, thermal properties, morphology, swelling properties, sustainable use, water retention, and biodegradation properties of SH. Additionally, the slow-release behavior of SHU was studied. SEM results revealed that SH possessed a porous three-dimensional network structure, with a maximum water absorption capacity of 4440 % ± 6.23 %. Compared to pure urea, SHU exhibited better slow-release performance after 30 days of release in soil, with SHU1 having a residual nitrogen content of specifically 36.01 ± 0.57 % of the initial nitrogen content. A pot experiment with pakchoi substantiated the water retention and plant growth promotion properties of SHU. This study demonstrated a straightforward method for the preparation of starch-based Schiff-base hydrogels as fertilizer carriers.

Injectable hydrogels embedded with chitosan nanoparticles coated with hyaluronic acid for sequential release of dual drugs

An effective treatment for some disease, such as the model disease acute retinal necrosis (ARN), requires a combination of different drugs which should be administered at a certain interval. The precise sequential and long-term drug release are the critical questions. In this work, the as-prepared chitosan nanoparticles (CS-NPs) coated with hyaluronic acid (HA) were embedded in the aldehyde β-cyclodextrin (ACD)/aminated hyaluronic acid (NHA) hydrogels to synthesize injectable hydrogels loaded with dual drugs named DEX-CS-NPs/GCV-Gel and HA-DEX-CS-NPs/GCV-Gel. In the first 24 h and 48 h, the releases of DEX from DEX-CS-NPs/GCV-Gel were 128.5 % and 82.8 % faster than those from HA-DEX-CS-NPs/GCV-Gel, respectively. There was no DEX released from HA-DEX-CS-NPs/GCV-Gel at the first 7 h, which has never been reported before, although some hydrogel systems loaded with different drugs release different drugs simultaneously at different rate which have been well studied. This is a good start of a precise sequence release. The composite hydrogels possessed appropriate rheology, gel time, degradation performance, and ideal cytocompatibility. The injectable hydrogel loaded with dual drugs presenting a precise sequential and long-term release has great potential in the treatment of diseases requiring combinations of drugs being released sequentially at different treating stages.

Significance of biopolymer-based hydrogels and their applications in agriculture: a review in perspective of synthesis and their degree of swelling for water holding

Hydrogels are three-dimensional polymer networks that are hydrophilic and capable of retaining a large amount of water. Hydrogels also can act as vehicles for the controlled delivery of active compounds. Bio-polymers are polymers that are derived from natural sources. Hydrogels prepared from biopolymers are considered non-toxic, biocompatible, biodegradable, and cost-effective. Therefore, bio-polymeric hydrogels are being extensively synthesized and used all over the world. Hydrogels based on biopolymers finds important applications in the agricultural field where they are used as soil conditioning agents as they can increase the water retention ability of soil and can act as a carrier of nutrients and other agrochemicals. Hydrogels are also used for the controlled delivery of fertilizer to plants. In this review, bio-polymeric hydrogels based on starch, chitosan, guar gum, gelatin, lignin, and alginate polymer have been discussed in terms of their synthesis method, swelling behavior, and possible agricultural application. The urgency to address water scarcity and the need for sustainable water management in agriculture necessitate the exploration and implementation of innovative solutions. By understanding the synthesis techniques and factors influencing the swelling behavior of these hydrogels, we can unlock their full potential in fostering sustainable agriculture and mitigating the challenges posed by an ever-changing environment.