Design and development of guar gum based novel, superabsorbent and moisture retaining hydrogels for agricultural applications

Optimization of biodegradable cross-linked guar-gum-PLA superabsorbent hydrogel formation employing response surface methodology

Cross-linked polymer networks with three-dimensional structures known as hydrogels absorb and retain a large amount of water. Because of their properties, hydrogel materials have been considered a boon in agriculture science. In the present investigation, guar gum cross-linked polylactic acid hydrogel is synthesized using MMA as monomer and optimized using a central composite design of response surface methodology for better swelling. The studied input variables are monomer concentration, initiator concentration, and cross-linker concentration at constant pH and temperature. The constructed response model has been tested using the analysis of variance (ANOVA), where the model F-value of 4.64 indicates that the model is significant. The R2 value (0.806) (multiple correlation coefficient) and the standard deviation for the quadratic model were both found to be 4.27. A separate validation experiment is conducted to ensure the quadratic model is sufficient. The hydrogel synthesis was confirmed by characterization techniques like FTIR spectroscopy, SEM, TGA, XRD, and water absorption studies. Synthesized hydrogels swell maximum in water and least in 0.9 % NaCl solution. The present work highlights the development of guar gum-based super-absorbent hydrogels, which are biodegradable and lead to potential application in agriculture, especially in drought regions.

Encapsulation with Natural Polymers to Improve the Properties of Biostimulants in Agriculture

Encapsulation in agriculture today is practically focused on agrochemicals such as pesticides, herbicides, fungicides, or fertilizers to enhance the protective or nutritive aspects of the entrapped active ingredients. However, one of the most promising and environmentally friendly technologies, biostimulants, is hardly explored in this field. Encapsulation of biostimulants could indeed be an excellent means of counteracting the problems posed by their nature: they are easily biodegradable, and most of them run off through the soil, losing most of the compounds, thus becoming inaccessible to plants. In this respect, encapsulation seems to be a practical and profitable way to increase the stability and durability of biostimulants under field conditions. This review paper aims to provide researchers working on plant biostimulants with a quick overview of how to get started with encapsulation. Here we describe different techniques and offer protocols and suggestions for introduction to polymer science to improve the properties of biostimulants for future agricultural applications.

Facile Access to Gleditsia microphylla Galactomannan Hydrogel with Rapid Self-Repair Capacity and Multicyclic Water-Retaining Performance of Sandy Soil

Sandy soil has poor water-holding performance, making it difficult for plants to survive, which worsens the deterioration of the ecological environment. Therefore, borax cross-linked Gleditsia microphylla galactomannan hydrogel (GMGH) was prepared, and its practicability as a water-retaining agent was analyzed. GMGH exhibited fast self-healing performance (150 s, ≈100%) and a high swelling index (88.70 g/g in pH 9). The feasibility of improving the water absorption and retention properties of sandy soil was explored by mixing different proportions (0.1, 0.3, 0.5 wt % sandy soil) of GMGH and sandy soil. The results showed that sandy soil had a more porous structure after adding 0.5 wt % GMGH, and its water absorption index increased from 15.68 to 38.12%. In an artificial climate box, the water-holding time of the sandy soil was extended from 3 to 23.5 days, and the cycles of water absorption and retention were more than 10 times. Therefore, GMGH has broad application prospects as a potential water-retaining agent for desertification control.

Environmentally friendly hydrogel: A review of classification, preparation and application in agriculture

Superabsorbent hydrogel (SH) is three-dimensional (3D) cross-linked hydrophilic polymer that can absorb and retain large quantities of water or other aqueous solutions. SH is made of water-affinity monomers and is widely used in biomedicine, wastewater treatment, hygiene and slow-release fertilizers (SRFs). This article focused on the preparation methods of SH, superabsorbent hydrogel composite and the application of SH in agriculture. By selecting various synthetic technologies and cross-linking agents, a series of chemical cross-linking or physical networks can be designed and tailored to meet specific applications. In view of the excellent characteristics of water absorption, biodegradability, water retention and slow-release capacity, SH occupies a dominant position in the SRFs market. In this work, the agricultural application of SH in double coated SRFs and nutrients carriers is also discussed. Some mechanisms related to the nutrient release were analyzed by mathematical models. In addition, some agronomic benefits of using superabsorbent hydrogels in improving water absorption, water holding capacity and increasing crop yields were also discussed. Although SH has certain shortcomings, from the perspective of long-term development, it will further show great potential in sustainable agriculture.

The Synthesis, Characterization, and Protein-Release Properties of Hydrogels Composed of Chitosan-Zingiber offcinale Polysaccharide

Most proteins given orally have low bioavailability and are easily eliminated by rapid metabolism in vivo. In order to immobilize the drug at the site of administration and delay its release, a natural, gentle release system was designed. In this study, a heteropolysaccharide (ZOP) was isolated from Zingiber officinale using an ultrasonic assisted extraction method. ZOP Ara = 1.97: 1.15: 94.33: 1.48: 1.07. The ZOP/Chitosan (CS) composite hydrogel was synthesized using epichlorohydrin (ECH) as a cross-linking agent. The structure, morphology, and water-holding capacity of the composite hydrogel were characterized. The data showed that the addition of ZOP improved the hardness and water-holding capacity of the material. A swelling ratio test showed that the prepared hydrogel was sensitive to pH and ionic strength. In addition, the degradation rate of the hydrogel in a phosphate-buffered saline (PBS) solution with a pH value of 1.2 was higher than that in PBS with pH value of 7.4. Similarly, the release kinetics of Bovine serum albumin (BSA) showed higher release in an acidic system by the hydrogel composed of ZOP/CS. The hydrogel prepared by this study provided a good microenvironment for protein delivery. In summary, this composite polysaccharide hydrogel is a promising protein-drug-delivery material.

Radiation Synthesis of Green Nanoarchitectonics of Guar Gum-Pectin/Polyacrylamide/Zinc Oxide Superabsorbent Hydrogel for Sustainable Agriculture

In the current study, the performance of superabsorbent hydrogel composites comprised of Guar gum-Pectin/Polyacrylamide/ZnO crosslinked with gamma irradiation (10 kGy) has been investigated for sustainable agriculture. The claimed composites (GG/PC/PAAm/ZnOx) were characterized by FTIR, TGA, and AFM. The swelling capacity data reveal that the equilibrium water swelling (EW) of the composites was increased by increasing the ZnO content from 600 to 1050 g/g for zero to the highest concentration of ZnO, respectively. Furthermore, the physical properties of the soil mixed with the hydrogels were improved; water holding capacity (WHC) increased to 66% and water retention (WR) kept at 15% after 20 days. The composites showed a good degradability in the biodegradation test. They also portrayed super-absorption capacity at three swelling/deswelling cycles. This advancement is important for reducing water consumption through the irrigation of arid lands. The prepared composites were proved as excellent candidates in sustainable agriculture applications.

Chitosan/guar gum-based thermoreversible hydrogels loaded with pullulan nanoparticles for enhanced nose-to-brain drug delivery

The biopolymers-based two-fold system could provide a sustained release platform for drug delivery to the brain resisting the mucociliary clearance, enzymatic degradation, bypassing the first-pass hepatic metabolism, and BBB thus providing superior bioavailability through intranasal administration. In this study, poloxamers PF-127/PF-68 grafted chitosan HCl-co-guar gum-based thermoresponsive hydrogel loaded with eletriptan hydrobromide laden pullulan nanoparticles was synthesized and subjected to dynamic light scattering, Fourier transform infrared spectroscopy, thermal analysis, x-ray diffraction, scanning electron microscopy, stability studies, mucoadhesive strength and time, gel strength, cloud point assessment, rheological assessment, ex-vivo permeation, cell viability assay, histology studies, and in-vivo Pharmacokinetics studies, etc. It is quite evident that CSG-EH-NPs T-Hgel has an enhanced sustained release drug profile where approximately 86 % and 84 % of drug released in phosphate buffer saline and simulated nasal fluid respectively throughout 48 h compared to EH-NPs where 99.44 % and 97.53 % of the drug was released in PBS and SNF for 8 h. In-vivo PKa parameters i.e., mean residence time (MRT) of 11.9 ± 0.83 compared to EH-NPs MRT of 10.2 ± 0.92 and area under the curve (AUC_tot) of 42,540.5 ± 5314.14 comparing to AUC_tot of EH-NPs 38,026 ± 6343.1 also establish the superiority of CSG-EH-NPs T-Hgel.

The Characteristics of Time-Dependent Changes of Coefficient of Permeability for Superabsorbent Polymer-Soil Mixtures

Water uptake dynamics of superabsorbent polymers (SAP) in soil is of key importance for the optimum application of these materials in environmental engineering and agriculture, so goal of this paper is to determine time dependent values of coefficient of permeability for various SAP-soil mixtures. Retaining water in soil is a key requirement in critical zones to support plant growth. There is an urgent need for technologies that can increase soil water retention, given the increasing prevalence of droughts and scarcity of clean water as the climate changes, combined with the rising demand for food by a growing world population. SAPs are materials that can absorb significant amounts of water, and thus have tremendous potential to help increase water retention in soil. However, while some studies have characterized the equilibrium swelling behavior of SAPs in soil, how their addition influences the time-dependent flow of water through soil remains poorly understood. Here, we address this gap in knowledge by directly measuring the coefficient of permeability of SAP-soil mixtures, testing different soil grain sizes, SAP grain sizes, and different SAP-soil ratios. We find that SAP addition can dramatically hinder the flow rate of water through soil—reducing the permeability by several orders of magnitude, and in some cases causing complete blockage of water infiltration, at mass fractions as small as 1%. In this scenario coefficient of permeability of 1.23 × 10⁻⁴ m/s dropped by a factor of ~10 after 14 min, a factor of ~100 after 36 min, and by nearly a factor of ~1000 after 63 min, eventually causing complete blockage of infiltration after 67 min. Authors concluded that in this particular situation the size and quantity of SAP particles was enough to nearly completely fill the available pore space resulting in rendering the soil column almost completely impermeable. Moreover, we demonstrate that these effects are well-described by a simple hydraulic model of the mutual interactions between SAP and soil grains, providing more generally-applicable and quantitative principles to model SAP-soil permeability in applications. Ultimately, this work could help evaluate the optimal proportions and grain sizes of SAPs to use for a given soil to simultaneously achieve a desirable permeability along with increased water holding capacity in the plant root zone.

Prospects of Hydrogels in Agriculture for Enhancing Crop and Water Productivity under Water Deficit Condition

In arid and semiarid regions and under rainfed conditions, water availability is one of the principal ecological constraints that hinder agriculture’s sustainability. The super absorbent polymer (agricultural) is water-absorbing and is cross-linked to absorb aqueous solutions through bonding with water molecules. It is a new approach to water management under water-stressed conditions to conserve soil moisture in the active rooting zone of crops by reducing the evaporation, deep percolation, and runoff losses. Agricultural hydrogels are water retention granules which swell their original size to numerous intervals when they come in contact with water. It can absorb and retain a huge amount of moisture under plentiful rainfall and irrigation events and release it back to the soil for mitigating crop water demand when the rhizosphere zone dries up under drought conditions. It plays multifarious roles in agriculture including soil-water retainer, nutrient and pesticide carriers, seed coating, soil erosion reducer, and food additives. It has the extraordinary ability in improving different physicochemical, hydrophysical, and biological properties of soil, simultaneously decreasing irrigation frequency, enhancing the water and nutrient use efficiencies, and increasing the yield and quality of the field, plantation, ornamental, and vegetable crops. These biodegradable materials are nontoxic to the soil, crop, and environment. Hence, the addition of the hydrogel polymer will be a promising and feasible technological tool for augmenting crop productivity under moisture stressed conditions.

Effects of Water-Retaining Agent Dosages on Slope-Protection Plants and Soil Nutrients on Rocky Slopes

Rocky slopes lack the necessary conditions for plant growth, i.e., soil and water, making vegetation recovery difficult and necessitating artificial soil conditions for vegetation establishment. Water-retaining agents are essential functional substances for constructing artificial soil on rocky slopes. In this study, the effect of water-retaining agents on the growth of artificial vegetation and soil nutrient loss was investigated by setting different application rates of water-retaining agents (10 g/m2, 20 g/m2, 30 g/m2, 40 g/m2, and 50 g/m2). Artificially simulated rocky slope conditions were achieved using the guest soil spraying technology after hanging the net, which provided support for the application of the water-retaining agent. Results showed that the contents of extractable nitrogen (EN), extractable phosphorus (EP), and extractable potassium (EK) in the soil, the number of plant individuals per unit area, plant height, and ground diameter of the water-retaining agent treatment were significantly higher than those of the control group (set up with no water retention as the control group, hereafter “CK”). By contrast, the nutrient content in the runoff fluid was significantly lower than that of CK. The application of the water-retaining agent significantly enhanced the soil’s ability to retain water and fertilizer, thus improving the growing environment and plant growth. Under the conditions of this experiment, the application rate of a 40 g/m2 water-retaining agent is reasonable from the perspectives of economic cost, soil nutrients, and plant growth.

DOE-based synthesis of gellan gum-acrylic acid-based biodegradable hydrogels: screening of significant process variables and in situ field studies

The current study uses the free radical graft copolymerization of acrylic acid as a monomer, N,N-methylene-bis-(acrylamide) as a crosslinker and ammonium persulfate as an initiator to synthesise GG-cl-poly(AA) hydrogels based on gellan gum utilising response surface methodology (RSM). A full factorial design was used to obtain the greatest percent swelling (P_s), and key process variables were determined using the Pareto chart. To make the procedure cost-effective, a multiple regression model employing ANOVA projected a linear model with a maximum percentage swelling of 556 at the lowest concentration of all three studied factors. As a result, the sequential experimental design was successful in obtaining two-fold increases in the percentage swelling in a systematic way. An RSM-based central composite design was used to optimize the percentage swelling of the three most important synthesis parameters: initiator concentration, monomer concentration, and crosslinker concentration. The best process conditions are 7.3 mM L⁻¹ initiator, 44 μM L⁻¹ monomer, and 21.6 mM L⁻¹ crosslinker. The effective synthesis of GG-cl-poly(AA) was validated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, field emission scanning electron microscopy (FE-SEM), and ¹H-nuclear magnetic resonance. The swelling behavior of GG-cl-poly(AA) in water and saline solutions, as well as its water retention capability, was investigated. In comparison to distilled water, the swelling potential of optimized hydrogel was shown to be significantly reduced in saline solutions. The addition of GG-cl-poly(AA) significantly improved the moisture properties of plant growth media (clay, sandy, and clay–soil combination), implying that it has great potential in moisture stress agriculture. GG-cl-poly(AA) biodegradation was studied by soil burial and vermicomposting methods. The composting approach showed 89.95% deterioration after 22 days, while the soil burial method showed 86.71% degradation after 22 days. The synthesized hydrogel may be beneficial for agricultural applications because of its considerable degradation behaviour, strong water retention capacity, low cost, and environmental friendliness.

We use free radical graft copolymerization of acrylic acid as a monomer, N,N-methylene-bis-(acrylamide) as a crosslinker and ammonium persulfate as an initiator to synthesise GG-cl-poly(AA) hydrogels based on gellan gum utilising response surface methodology.

Synthesis, characterization and biocompatibility of guar gum-benzoic acid

A novel chemical functionalization of guar gum (GG) by benzoic acid (BA) via nucleophilic substitution reaction in aqueous solution has been reported. BA moieties are chosen due to coordination chemistry of carboxylic acid moieties, hydrophobicity and intermolecular interaction of aromatic rings. The presence of conjugated BA on guar gum-benzoic acid (GG-BA) with grafting density of 5.5% is confirmed by ¹H NMR. Amorphous GG-BA with irregular morphology has been studied by UV-Vis, FTIR, XRD, SEM, TEM, TGA, computational chemistry and contact angle measurement. GG-BA in a concentration range from 0 to 4000 μg mL^-1 has good biocompatibility to mouse embryonic fibroblasts (MEF), human mammary epithelial cells (MCF-10A) after 48 and 72 h of treatment using WST-1 assay. GG-BA shows great potential for the development of biomaterials such as bioadhesives, hydrogels, and coacervates.

Synthesis of Superabsorbent Polymer Hydrogels with Rapid Swelling: Effect of Reaction Medium Dosage and Polyvinylpyrrolidone on Water Absorption Rate

A superabsorbent polymer (SAP) was synthesized by solution polymerization. The influence of synthesis technology was studied and optimized, and FTIR, SEM, and TGA were used to characterize the structure and morphology of the material. Under the optimal synthesis conditions, the water absorption of the material can achieve about 80% of the saturation value in the first 20 min, and the material absorbs distilled water up to 2013 g/g. The SAP also has remarkable water retention and reswelling capability. The excellent performance makes it have a promising application in agriculture. In addition, the results show that the dosage of the reaction medium is a major factor for performance. Under the condition of the optimum value of other factors, the influence of the dosage of the reaction medium on water absorption can reach about 1000 g in distilled water.

Guar (Cyamopsis tetragonoloba L.) plant gum: From biological applications to advanced nanomedicine

Natural polymers are an efficient class of eco-friendly and biodegradable polymers, because they are readily available, come from natural sources, inexpensive and can be chemically modified with the correct reagents. Guar gum (GG) is a natural polymer with great potential to be used in pharmaceutical formulations due to its unique composition and lack of toxicity. GG can be designed to suit the needs of the biological and medical engineering sectors. In the development of innovative drug delivery systems, GG is commonly utilized as a rate-controlling excipient. In this review, different properties of GG including chemical composition, extraction methods and its usefulness in diabetes, cholesterol lowering, weight control, tablet formulations as well as its food application were discussed. The other purpose of this study is to evaluate potential use of GG and its derivatives for advanced nanomedicine such as drug delivery, tissue engineering and nanosensing. It should be noted that some applicable patents in medical area have also been included in the rest of this survey to extend knowledge about guar gum and its polymeric nature.

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.

Albumin Microspheres as "Trans-Ferry-Beads" for Easy Cell Passaging in Cell Culture Technology

Protein hydrogels represent ideal materials for advanced cell culture applications, including 3D-cultivation of even fastidious cells. Key properties of fully functional and, at the same time, economically successful cell culture materials are excellent biocompatibility and advanced fabrication processes allowing their easy production even on a large scale based on affordable compounds. Chemical crosslinking of bovine serum albumin (BSA) with N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDC) in a water-in-oil emulsion with isoparaffinic oil as the continuous phase and sorbitan monooleate as surfactant generates micro-meter-scale spherical particles. They allow a significant simplification of an indispensable and laborious step in traditional cell culture workflows. This cell passaging (or splitting) to fresh culture vessels/flasks conventionally requires harsh trypsinization, which can be omitted by using the “trans-ferry-beads” presented here. When added to different pre-cultivated adherent cell lines, the beads are efficiently boarded by cells as passengers and can be easily transferred afterward for the embarkment of novel flasks. After this procedure, cells are perfectly viable and show normal growth behavior. Thus, the trans-ferry-beads not only may become extremely affordable as a final product but also may generally replace trypsinization in conventional cell culture, thereby opening new routes for the establishment of optimized and resource-efficient workflows in biological and medical cell culture laboratories.

Swelling and kinetic investigations of basic blue-3 sorption by polyacrylamide/Gum Arabic hybrid hydrogel in aqueous medium

Removal of noxious dyes from waste water is highly desirable for the safety of humans, aquatic life and natural environment. The issue was addressed in the present work by one pot fabrication of polyacrylamide/Gum Arabic (pAAm/GA) composite hydrogel which was applied as sorbent for basic blue-3 (BB3) eradication. The synthesis of the material was confirmed by scanning electron microscopy (SEM), Fourier Transformed Infrared (FTIR) spectroscopy and thermo gravimetric analysis (TGA). Besides, the same techniques also evidenced BB3 uptake by the hydrogel. In distilled water, the swelling capacities of the hydrogel was investigated at pH 7 and the nature of water diffusion into the hydrogel was probed from the resultant data. The composite hydrogel reached equilibrium point in 24 h after which no appreciable water absorption occurred. The adsorption of BB3 by the hybrid material was comprehensively investigated which involved the effect of contact time, temperature and pH on the sorption capacity of the hybrid sorbent. The obtained data fitted well into pseudo second order kinetic model and the adsorption took place in three consecutive kinetic phases. Moreover, sorption thermodynamics revealed non spontaneous and endothermic nature of BB3 sorption accompanied with increase in degree of order.

Water-soluble polymers in agriculture: xanthan gum as eco-friendly alternative to synthetics

Water-soluble polymers (WSPs) are a versatile group of chemicals used across industries for different purposes such as thickening, stabilizing, adhesion and gelation. Synthetic polymers have tailored characteristics and are chemically homogeneous, whereas plant-derived biopolymers vary more widely in their specifications and are chemically heterogeneous. Between both sources, microbial polysaccharides are an advantageous compromise. They combine naturalness with defined material properties, precisely controlled by optimizing strain selection, fermentation operational parameters and downstream processes. The relevance of such bio-based and biodegradable materials is rising due to increasing environmental awareness of consumers and a tightening regulatory framework, causing both solid and water-soluble synthetic polymers, also termed 'microplastics', to have come under scrutiny. Xanthan gum is the most important microbial polysaccharide in terms of production volume and diversity of applications, and available as different grades with specific properties. In this review, we will focus on the applicability of xanthan gum in agriculture (drift control, encapsulation and soil improvement), considering its potential to replace traditionally used synthetic WSPs. As a spray adjuvant, xanthan gum prevents the formation of driftable fine droplets and shows particular resistance to mechanical shear. Xanthan gum as a component in encapsulated formulations modifies release properties or provides additional protection to encapsulated agents. In geotechnical engineering, soil amended with xanthan gum has proven to increase water retention, reduce water evaporation, percolation and soil erosion - topics of high relevance in the agriculture of the 21st century. Finally, hands-on formulation tips are provided to facilitate exploiting the full potential of xanthan gum in diverse agricultural applications and thus providing sustainable solutions.

Formulation and In-Vitro Characterisation of Cross-Linked Amphiphilic Guar Gum Nanocarriers for Percutaneous Delivery of Arbutin

Nano-colloidal systems formulated from amphiphilically-modified polysaccharides (degree of modification 16.6%) are focus of prominent study due to their potential to augment active penetration across the skin. Here we report the synthesis of amphiphilically-modified guar gum (GBE-GG) prepared by grafting with glycidol butyl ether (GBE), which were subsequently formed into nanocarriers and loaded with α-arbutin (22.3% loading). The monodispersed and close-to-spherical nanocarriers (size range 239-297 nm) formed via cross-linking were adequately stable mainly at low temperature (4 °C) under physiological pH condition. α-arbutin was released from GBE-GG NPs in a more sustained manner and the release profiles can be accurately represented by the 1^st order kinetic model. In-vitro interactions on immortalised human keratinocytes (HaCaT) cells revealed an increase in biological membrane permeability as well as the absence of cellular toxicity at application pertinent concentrations. No substantial haemolytic activity appeared and flow cytometry analysis revealed effective cellular uptake, suggesting their potential as promising nanocarriers for percutaneous delivery that warrants further comprehensive research.

Advances and Novel Perspectives on Colloids, Hydrogels, and Aerogels Based on Coordination Bonds with Biological Interest Ligands

This perspective article shows new advances in the synthesis of colloids, gels, and aerogels generated by combining metal ions and ligands of biological interest, such as nucleobases, nucleotides, peptides, or amino acids, among other derivatives. The characteristic dynamism of coordination bonds between metal center and biocompatible-type ligands, together with molecular recognition capability of these ligands, are crucial to form colloids and gels. These supramolecular structures are generated by forming weak van der Waals bonds such as hydrogen bonds or π–π stacking between the aromatic rings. Most gels are made up of nano-sized fibrillar networks, although their morphologies can be tuned depending on the synthetic conditions. These new materials respond to different stimuli such as pH, stirring, pressure, temperature, the presence of solvents, among others. For these reasons, they can trap and release molecules or metal ions in a controlled way allowing their application in drug delivery as antimicrobial and self-healable materials or sensors. In addition, the correct selection of the metal ion enables to build catalytic or luminescent metal–organic gels. Even recently, the use of these colloids as 3D-dimensional printable inks has been published. The elimination of the solvent trapped in the gels allows the transformation of these into metal–organic aerogels (MOAs) and metal–organic xerogels (MOXs), increasing the number of possible applications by generating new porous materials and composites useful in adsorption, conversion, and energy storage. The examples shown in this work allow us to visualize the current interest in this new type of material and their perspectives in the short-medium term. Furthermore, these investigations show that there is still a lot of work to be done, opening the door to new and interesting applications.

Curcumin-laden hyaluronic acid-co-Pullulan-based biomaterials as a potential platform to synergistically enhance the diabetic wound repair

Injectable hydrogel with multifunctional tunable properties comprising biocompatibility, anti-oxidative, anti-bacterial, and/or anti-infection are highly preferred to efficiently promote diabetic wound repair and its development remains a challenge. In this study, we report hyaluronic acid and Pullulan-based injectable hydrogel loaded with curcumin that could potentiate reepithelization, increase angiogenesis, and collagen deposition at wound microenvironment to endorse healing cascade compared to other treatment groups. The physical interaction and self-assembly of hyaluronic acid-Pullulan-grafted-pluronic F127 injectable hydrogel were confirmed using nuclear magnetic resonance (¹H NMR) and Fourier transformed infrared spectroscopy (FT-IR), and cytocompatibility was confirmed by fibroblast viability assay. The CUR-laden hyaluronic acid-Pullulan-g-F127 injectable hydrogel promptly undergoes a sol-gel transition and has proved to potentiate wound healing in a streptozotocin-induced diabetic rat model by promoting 93% of wound closure compared to other groups having 35%, 38%, and 62%. The comparative in vivo study and histological examination was conducted which demonstrated an expeditious recovery rate by significantly reducing the wound healing days i.e. 35 days in a control group, 33 days in the CUR suspension group, 21 days in unloaded injectable, and 13 days was observed in CUR loaded hydrogel group. Furthermore, we suggest that the injectable hydrogel laden with CUR showed a prompt wound healing potential by increasing the cell proliferation and serves as a drug delivery platform for sustained and targeted delivery of hydrophobic moieties.

Diffusion of water and protein drug in 1,4-butanediol diglycidyl ether crosslinked galactomannan hydrogels and its correlation with the physicochemical properties

The aim of the present study was to obtain a better and safer galactomannan-based material for drug release applications. A novel epoxy-crosslinked galactomannan hydrogel (EGH) was prepared from guar gum using 1,4-butanediol diglycidyl ether as a crosslinking agent. The diffusion rate constant of water molecules in freeze-dried EGH positively correlated with water uptake/equilibrium swelling rate (WU/ESR), and the water molecules participated in Fickian diffusion. The ESR, WU/ESR, and bovine serum albumin (BSA) loading capacity of a customized EGH with a crosslinking density of 48.9% were 48.7 ± 0.15 g/g, 95.3%, and 56.4 mg/g, respectively. The release of BSA from freeze-dried EGH was affected by the WU/ESR and the pH; the release equilibrium time was ~40 h at pH 1.2, decreasing to ~24 h at pH 7.4. Furthermore, the cumulative release rate increased from 63.5% to 80.7% and the t₅₀ decreased from 59 to 41 min upon changing from the acidic to basic pH. The release process conformed to the Ritger-Peppas and Hixson-Crowell models, and represented Fickian diffusion and chain relaxation. The EGH showed no cytotoxicity toward HeLa cells. Together, these results demonstrate the properties of a novel galactomannan-based hydrogel that can potentially be employed as a vehicle for drug delivery.

Superabsorbent Hydrogels Based to Polyacrylamide/Cashew Tree Gum for the Controlled Release of Water and Plant Nutrients

Agricultural production is influenced by the water content in the soil and availability of fertilizers. Thus, superabsorbent hydrogels, based on polyacrylamide, natural cashew tree gum (CG) and potassium hydrogen phosphate (PHP), as fertilizer and water releaser were developed. The structure, morphology, thermal stability and chemical composition of samples of polyacrylamide and cashew tree gum hydrogels with the presence of fertilizer (HCGP) and without fertilizer (HCG) were investigated, using X-ray diffractometry (XRD), Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA/DTG) and Energy Dispersive Spectroscopy (EDS). Swelling/reswelling tests, textural analysis, effect of pH, release of nutrients and kinetics were determined; the ecotoxicity of the hydrogels was investigated by the Artemia salina test. The results showed that PHP incorporation in the hydrogel favored the crosslinking of chains. This increased the thermal stability in HCGP but decreased the hardness and adhesion properties. The HCGP demonstrated good swelling capacity (~15,000 times) and an excellent potential for reuse after fifty-five consecutive cycles. The swelling was favored in an alkaline pH due to the ionization of hydrophilic groups. The sustained release of phosphorus in HCGP was described by the Korsmeyer-Peppas model, and Fickian diffusion is the main fertilizer release mechanism. Finally, the hydrogels do not demonstrate toxicity, and HCGP has potential for application in agriculture.

Proteins from Agri-Food Industrial Biowastes or Co-Products and Their Applications as Green Materials

A great amount of biowastes, comprising byproducts and biomass wastes, is originated yearly from the agri-food industry. These biowastes are commonly rich in proteins and polysaccharides and are mainly discarded or used for animal feeding. As regulations aim to shift from a fossil-based to a bio-based circular economy model, biowastes are also being employed for producing bio-based materials. This may involve their use in high-value applications and therefore a remarkable revalorization of those resources. The present review summarizes the main sources of protein from biowastes and co-products of the agri-food industry (i.e., wheat gluten, potato, zein, soy, rapeseed, sunflower, protein, casein, whey, blood, gelatin, collagen, keratin, and algae protein concentrates), assessing the bioplastic application (i.e., food packaging and coating, controlled release of active agents, absorbent and superabsorbent materials, agriculture, and scaffolds) for which they have been more extensively produced. The most common wet and dry processes to produce protein-based materials are also described (i.e., compression molding, injection molding, extrusion, 3D-printing, casting, and electrospinning), as well as the main characterization techniques (i.e., mechanical and rheological properties, tensile strength tests, rheological tests, thermal characterization, and optical properties). In this sense, the strategy of producing materials from biowastes to be used in agricultural applications, which converge with the zero-waste approach, seems to be remarkably attractive from a sustainability prospect (including environmental, economic, and social angles). This approach allows envisioning a reduction of some of the impacts along the product life cycle, contributing to tackling the transition toward a circular economy.

Starch-Based Super Water Absorbent: A Promising and Sustainable Way to Increase Survival Rate of Trees Planted in Arid Areas

This research aimed to scale up the production of starch-based super water absorbent (SWA) and to validate the practical benefits of SWA for agricultural applications. SWA was successfully prepared in an up-scaling production by radiation-induced graft polymerization of acrylic acid onto cassava starch. Chemical characterization by FTIR and thermal characterization by TGA showed results that differentiated starting materials from the prepared SWA, thus confirming effective preparation of starch-based SWA via radiation-induced graft polymerization. SEM results visibly revealed a highly porous morphology of the synthesized SWA, substantiating its high swelling ability. Results from the field tests, performed for two seasons, revealed that the prepared SWA was able to increase the survival rate of young rubber trees planted in arid area by up to 40%, while simultaneously enhancing the growth characteristics of the young rubber trees.

Applications of Absorbent Polymers for Sustainable Plant Protection and Crop Yield

Natural strategies for protecting the environment as well as plant, animal and human health is considered one of the main goals of developed countries. Recently, the use of absorbent polymers and hydrogel in agriculture has demonstrated several benefits for soil amendments, saving water content, reducing the consumption of soil nutrients, minimizing the negative impacts of dehydration and moisture stress in crops and controlling several phytopathogens. The seed-coating technology for establishing the crops is a recent common practice used for improving seed protection and enhancing plant growth. Coating materials include absorbent polymers and hydrogels based on growth regulators, pesticides, fertilizers and antagonist microorganisms. The current review has highlighted the importance of different types of superabsorbent polymers and hydrogels in an integrated strategy to protect seeds, plants and soil in a balanced manner to preserve the ecosystem.

Design of facile technology for the efficient removal of hydroxypropyl guar gum from fracturing fluid

With the increasing demand for energy, fracturing technology is widely used in oilfield operations over the last decades. Typically, fracturing fluids contain various additives such as cross linkers, thickeners and proppants, and so forth, which makes it possess the properties of considerably complicated components and difficult processing procedure. There are still some difficult points needing to be explored and resolved in the hydroxypropyl guar gum (HPG) removal process, e.g., high viscosity and removal of macromolecular organic compounds. Our works provided a facile and economical HPG removal technology for fracturing fluids by designing a series of processes including gel-breaking, coagulation and precipitation according to the diffusion double layer theory. After this treatment process, the fracturing fluid can meet the requirements of reinjection, and the whole process was environment friendly without secondary pollution characteristics. In this work, the fracturing fluid were characterized by scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy technologies, etc. Further, the micro-stabilization and destabilization mechanisms of HPG in fracturing fluid were carefully investigated. This study maybe opens up new perspective for HPG removal technologies, exhibiting a low cost and strong applicability in both fundamental research and practical applications.

Preparation of urea-containing starch-castor oil superabsorbent polyurethane coated urea and investigation of controlled nitrogen release

With the aim of improving water absorption and controlled release performance of current controlled release fertilizers, a novel composite coating method for superabsorbent-polyurethane coated urea (SAPCU) was developed. Superabsorbent-polyurethane (SAPU) composite coating material was successfully formed through an insitu reaction, where castor oil polyurethane (COP) and superabsorbent polymer (SAP) were connected through urethane bonds with an optimal reaction ratio of SAP and PAPI as 2.5:1 (w w^-1). The ideal nitrogen release and water absorption characteristics of SAPCU were achieved by adjusting the amount of COP and SAPU. The SAPCU had a high total nitrogen content (40.23-42.14 %), large swelling ratios (120-160 g water/g SAPU), and long nitrogen release period (60-150 days).

Guar gum based hydrogel as controlled micronutrient delivery system: Mechanism and kinetics of boron release for agricultural applications

A boron loaded super-absorbent hydrogel (BLSAH) was developed through in situ incorporation of boron (B) in a guar gum-based hydrogel and characterized with FTIR, thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), and swelling studies, showing maximum absorption up to 356 g/g. The release pattern of B from the BLSAH and its kinetics was studied in water as well as soil. The B release pattern of the BLSAH was also compared with the commercial B fertilizer, boronated single super phosphate (bSSP). The BLSAH, following the Fickian mechanism, released 38% B, as compared with 51% of the bSSP, during the incubation period of 30 days in soil. The half-life period for the BLSAH (96.25 days) in soil was almost triple that of the bSSP's half-life (33.32 days), which is indicative of the slow and controlled release of B from the BLSAH. Thus, owing to its sustained nutrient release ability, the synthesized BLSAH exhibited wide potential for applications in agriculture sector.

Microencapsulated soil conditioner with a water-soluble core: improving soil nutrition of crop root

Traditional level of fertilisers was used by most farmers in China with the risks about resources wasting, environmental pollution together with soil structure deterioration. It is practicable to tackle the challenges about over-fertilisation and low efficiency with microencapsulated soil conditioner (MSC), which clads the water soluble core with natural polymer. Fulvic acid (FA) can be used as core material, because it possesses the characteristics of water-soluble, fertiliser maintenance and expedient monitoring. The morphology, structure, and properties of MSC were studied and compared. The particle size of MSC was ranged from 1.58 to 2.14 mm with a similar shape which was obtained by conventional measuring method due to their soft features. This was mainly attributed to the concentration of liquid paraffin and the interaction between shell materials and calcium chloride_. FTIR spectra showed that a peak appeared at 1372 cm^-1, and this was ascribed to the microcapsules crosslinked and solidified by calcium ions. Sustained release experiment revealed that the microcapsules owned better fertiliser-retaining and water-retaining performances, and FA may be released as long as 750 h. Biodegradation experiments revealed that an obvious pore structure was found on the surface of microspheres after 30 d of degradation, and this was consistent with the sustained release experiment. Pot experiment illustrated that the plants cured with the microcapsules showed significant growth trend and grew up to 9.2 cm with a maximum rate, and this revealed that MSC owned better performance of promoting the growth of crop root.