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To investigate the effect of droughtstress on chlorophyll content, enzymatic responses and some growth characteristics of Acacia victoriae seedlings and the effect of super-absorbent polymers (SAP) in reducing drought stress, a split plot experiment based on the completely randomized design was conducted. The treatments included four levels of drought stress (15, 30, 60 and 100% of field capacity) and four levels of SAP (0, 0.2, 0.4 and 0.6% weight percentages). The results of ANOVA showed a significant effect of drought stress on all growth characters, chlorophyll content and catalase and peroxidase enzymes activity, while the SAP didn't show any significant effect on the weight and areas of the leaves. The interaction effect between drought stress and SAP on the weight, number of leaves, proportion of root dry weight to aerial organs, chlorophyll and peroxidase enzyme activity was also significant. The effect of drought stress on reducing the number of the leaves, leaf area, length, volume and surface of roots and also increasing the root dry weight to aerial organs dry weight ratio, amount of chlorophyll and activity of antioxidant enzymes was significant. The different levels of SAP could absorb and hold water and consequently reduce the effect of drought stress and improve the growth characteristics and reduce the activity of catalase and peroxidase enzymes.

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In this study, phenolic compounds-coated ZnO@HAP nanocomposite (Ph.ZnO@HAP) was synthesized and used to improve the physical and chemical properties of chitosan hydrogel for biological application. At first, the phenolic compounds were extracted from walnut green hulls. The synthesis of Ph.ZnO@HAP nanocomposite was performed with the assistance of extracted phenols using a hydrothermal method. Chitosan hydrogel was also prepared using NaHCO₃ at 37°C. Hybrid hydrogels based on chitosan and Ph.ZnO@HAP nanocomposite were prepared in a similar way and then characterized by fourier-transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The antioxidant property, cytotoxicity, and osteogenesis of hybrid hydrogels were measured using DPPH radical scavenging method, MTT, and alkaline phosphatase enzyme assay, respectively. The FTIR spectra, FESEM images, EDX spectrum, and Zeta potential data showed that Ph.ZnO@HAP nanocomposites synthesized successfully with rod-like morphology, phenolic compounds coated on the surface and a negative particle surface charge. The results of DPPH experiment showed that the antioxidant property of the nanocomposite material increased in a concentration-dependent manner. The FESEM images of chitosan hybrid hydrogels with different concentrations of embedded Ph.ZnO@HAP nanocomposite showed that hybrid hydrogels have a more uniform porous structure, compared to the chitosan hydrogel. Moreover, by an increase in the nanocomposite concentration in the structure of hybrid hydrogels, the antioxidant property augmented. The results of the biological studies showed that the cytotoxicity of hybrid hydrogels on osteoblast-like cells (Saos-2) is lower than that of chitosan hydrogel. Also, hybrid hydrogels showed the higher potential in induction of osteogenesis than chitosan hydrogels.
 

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Superabsorbent hydrogel is a three-dimensional hydrophilic polymer that can absorb and store large amounts of water and aqueous solutions. Among various polymers, the chitosan as a biodegradable and non-toxic polymer has been widely used to fabricate superabsorbent hydrogels. In this research, a nanohydrogel composed of chitosan, acrylic acid and silver nanoparticles was synthesized by radical polymerization at 60 C^o. Swelling properties of chitosan/nanosilver/acrylic acid hydrogel were studied and then this hydrogel was treated under  ultrasonication. Finally, this hydrogel was coated on paper samples with 0, 1, 1.5 and 2 w % of hydrogel. FTIR spectroscopy was used to determine the functional groups and dynamic light scattering method (DLS) was applied to identify the size of hydrogel’s nano and microparticles The images of scanning electron microscopy (SEM) showed a hydrogel coating on paper and water stress tests revealed that adding 0% to 1.5 w% of nanohydrogels to the paper surface increased its water absorption from 64.3% to 95.5%. Other worthwhile fact was that that the addition of silver nanoparticles effectively facilitated the formation of a three-dimensional hydrogel structure and increased the water swelling in nanohydrogel from 130 ± 10 g / g to 232 ± 7 g / g.

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Research Subject: Poor mechanical strengths and lack of thermal stabilities of hydrogels confine their extensive practical applications in many areas. The growing scientific need for solving this problem and achievement to the hydrogels with improved properties has led to the design and production of the nanocomposite hydrogels.
Research Approach: The polymeric networks of nanocomposite hydrogels compared to the ordinary hydrogels have improved elasticity and rheological properties. Other points that increase the importance of structural studies of nanocomposite hydrogels are the high strength of these materials versus the application of external forces, as well as maintaining its structure against increasing of temperatures. In this regard, the type and amounts of nanomaterial, the preparation method and formation of hydrogel network have a significant role in improving the physical, chemical and biological properties of hydrogels, and, it must be noted that these parameters will depend on the application of nanocomposite hydrogels. This also highlights the need for the production of nanocomposite tailored hydrogels. Therefore, orientation of the range of nanomaterials, the preparation method and product identification, along with sufficient information on the application of these materials, might have an important role in ensuring the success of these materials, requiring comprehensive library research and studies on polymerization processes, morphology and rheology.
Main Results: In this review article, the scientific advances in the field of nanocomposite hydrogels, focusing on its types based on the type of nanoparticles, its properties, preparation methods, identification methods with a new perspective on rheology, thermal analysis and morphology is investigated. Finally, the applicability of these materials is collected in a comprehensive table in various fields such as tissue engineering, enhanced oil recovery, agriculture, and etc…

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Research subject: Superabsorbents are hydrophilic hydrogels that can accommodate large amounts of water in their three-dimensional structures and have wide applications in various sciences such as pharmaceuticals, medicine, and agriculture. These materials are hydrophilic polymers that are physically or chemically cross-linked. Conversion and swelling ratio of synthesized hydrogels are two counter effects. Therefore, determining the appropriate conditions for polymerization to achieve optimal properties and swelling rate of hydrogels is a challenge for researchers.
Research approach: In this study, optimizing the synthesis conditions of semi-interpenetrating poly (acrylic acid)/xanthan hydrogels, the response surface methodology (RSM) was used by Box-Behnken design (BBD). The variables of this method were the molar ratio of the cross-linking agent (X₁), the weight percentage of xanthan gum (X₂) as the reaction medium, and the amount of initiator (X₃), each of which was considered at three levels. The evaluated responses in RSM were the rate of polymerization conversion (Y₁) and the rate of swelling (Y₂) of the hydrogels in the water.
 
Main results: Based on the 17 experiments proposed by RSM (BBD), the cross-linker, xanthan gum, and initiator were combined and radical polymerization was performed into silicone molds at 65 ° C. The results of ANOVA analysis showed that the data error of this study was small and the coefficient of determination (R2) of both proposed models for the responses Y₁ and Y₂ was higher than 0.9. The 46 experiments proposed for the optimal point by RSM (BBD) with the desirability of more than 50% indicate the synthesis of hydrogels that have both a good conversion rate and an optimal amount of swelling. For example, by 13% of cross-linking agent, 0.043 g of initiator and 1% wt. the solution of xanthan, hydrogels with a 95% conversion rate, and 102% water uptake were prepared. These hydrogels can be used in a variety of fields, including the treatment of colored wastes in factories, agriculture, pharmaceutical systems, medical attractions, and more.

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Research Subject: Global energy demand is increasing, so enhanced oil recovery techniques have incorporated in production processes. Water flooding is a common technique in oil recovery processes. One of the major challenges in this technique is heterogeneity of the reservoir structure which results in increased water production and reducing the oil recovery factor. Moreover, long-term water or chemical injection might lead to the increased horizontal and vertical heterogeneities in the reservoir. Selective blockage of high permeability areas and consequently improved production from low permeability regions is important for increasing the oil recovery factor. In recent years, using hydrogels in injection processes, has been associated with various field successes, indicating the ability of these materials for selectively blocking the areas of high permeability. Hydrogels are injected after water or polymer flooding to conduct the injected fluid to low permeability areas.
Research Approach: In this paper, hydrogel injection process was simulated in glass micromodels using Comsol Multiphysics software. Hydrogel functionality was studied in low permeability areas in porous media. Moreover, the optimized conditions for water flooding process was studies. For this purpose, after model validation, sensitivity analysis was performed on effective parameters on oil recovery factor and a mathematical model was presented to predict the oil recovery factor.
Main Results: Oil recovery factors obtained from experimental and simulation studies, were in good agreement with each other with absolute error values of 2.29% and 4.06%, for water and hydrogel flooding, respectively.
Four parameters of injection rate, contact angle, oil viscosity, and injection fluid viscosity were considered as effective parameters on oil recovery factor. Among them, contact angle was the most important parameter. In water flooding, the most important interacting parameters are viscosity and contact angle and the least important parameters are injection temperature and rate. In water flooding simulation studies, the thickness of the contact surface was obtained hmax/5, where  is 230 micrometers. For hydrogel injection, the contact surface thickness was obtained terpf.ep_default / 5.65. Terpf.ep_default is the thickness of contact surface, equal to 631 micrometers

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One of the problems related to oil recovery is water production, which reduces the production life of oil reservoirs and wells. Nowadays, the polymer gel injection method is used to control water production in the reservoir. In this study, an attempt has been made to investigate the rheological properties of xanthan-based hydrogels, considering Iran's reservoirs and also due to the existence of environmental problems in the field of synthetic polymers. The strength and stability of hydrogels can be applied by changing environmental conditions as a function of time and shear rate. For this purpose, the viscoelastic properties of hydrogels, including the elastic and viscous modulus, have been studied in relation to temperature, time and deformation rate for the gelant solution. Also, the effect of the composition of hydrogels, including the polymer concentration, the weight ratio of the crosslinking agent to the polymer, and the weight percentage of silica nanoparticles was considered in the study of rheological properties. Additionally, gelation time has been studied as one of the most important determining parameters of hydrogel during injection in porous medium. 

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Controlled delivery technology of protein/peptide drugs from biodegradable particles has emerged as one of the eminent areas to overcome problems related to macromolecules formulation. The goal of the present study was to develop protein-loaded micro-particles using biodegradable polymer, polycaprolactone (PCL) and hydrogel from beluga cartilage. Bovine serum albumin (BSA) was used as a model for protein/ peptide molecules such as GnRH. The double emulsion (W/O/W) technique was selected as one of the most appropriate methods for preparing a drug delivery system for soluble proteins in water. The first emulsion was prepared using ultrasonic and the mechanical agitator was used for achieving the second emulsion. The hydrogel prepared by enzymatic digestion was used in the first aquatic solution. At the present investigation, three groups were considered as the drug delivery system: G1; (PCL/hydrogel/BSA), G2; (PCL/BSA) and G3; (PCL/Alginate/BSA). Findings showed that the morphology of particles was spherical and non-conglomerated in all groups. The comparison of average particle size among groups was also indicated that the particles.

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Mercury is one of the most harmful pollutants in the environment, which in the event of ingestion into the human body, it is not metabolized and severe nervous, respiratory and metabolic disorders will occur due to the formation of stable complexes with biological molecules. Therefore, the development of precise, fast and inexpensive methods for mercury detection in the environment is of great importance. Carbon quantum dot is a new fluorescent substance with unique physical and chemical properties which is taken into consideration for diagnostic applications, especially for heavy metals detection at low concentrations. In this study, carbon dots with blue fluorescent emission were synthesized using the pyrolysis method and characterized. Fluorescent emission intensity of synthesized carbon dots was decreased significantly in interacting with mercury. Then for providing an easy-to-use mercury detection method, carbon dot was encapsulated in sodium alginate hydrogel. Quenching fluorescent intensity of encapsulated carbon dots in the hydrogel structure was evaluated in the presence of mercury and 1micromolar detection limit was obtained. Encapsulating carbon dots in hydrogel structure not only extend the use of carbon dot as a mercury sensor but also can be used as an adsorbent for mercury pollutant from the environment.
 

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The human amniotic membrane (HAM) is one of the rare allograft tissues that are in use in clinical trials. Biocompatibility, antibacterial effect, low immunogenicity, and scar prevention are properties that have made HAM attractive for tissue engineering (TE) applications, for example, as a cell carrier, injectable hydrogel, and cell culture substrate. In this research, the effect of digestion time on the structure, gelation kinetics, rheological and biological properties of amniotic membrane-derived hydrogels was studied. The results determined that digestion with pepsin should be performed at least for 24 h.  Prolonging the digestion time to 72 h increased the shear modulus, fiber diameter, and gelation rate. Cytocompatibility assays with L929 fibroblast cells showed that the digestion time had no effect on the cell toxicity of the hydrogels. However, cell proliferation was improved due to preserved constitutive bioactive molecules. The results of this research can be used to develop amniotic membrane-derived hydrogels for TE applications.

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Designing new drug delivery systems is important; therefore, in the present study the interaction between an anti-cancer drug, bicalutamide, and an amide/acid hydrogel was studied. Analyzing was done by using docking and molecular dynamics simulation methods. Molecular dynamics simulations were performed at 37 and 42 °C. The results showed that the binding free energies of the drug to the hydrogel system at two temperatures were similar, and altering the temperature did not affect the stability of the system. The van der Waals interaction is the most crucial interaction between the drug and the hydrogel, which depends on the distance between the drug and hydrogel. Intra- and intermolecular hydrogen bonds and van der Waals interactions, are the major factors in the stability of the hydrogel system. Due to the stability of the studied system, it can be used as a drug carrier.
 

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In this study, the complex coacervation of plantago major seed mucilage (PSM) and chitosan (CHI), two oppositely charged polysaccharides, was studied as a function of pH (8.0-2.0). Biopolymers concentration 1% and PSM:CHI ratio (10:90 to 90:10), according to electrical conductivity (EC) and turbidity analyses. The solution containing 1% biopolymers with PSM:CHI ratio of 85:15 resulted in maximum complex coacervation at the pHopt 3.7. The EC of biopolymers solutions increased by decreasing pH. The aforementioned optimum condition resulted coacervates with maximum particles size (7 μm) and minimum ζ-potential (+5.5 mV), which were observed as densely agglomerated macro-complexes with highest coacervation yield (87%).
These hydrogels be useful for encapsulation and delivery of drugs and (bio-) active compounds.

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Gelatin is mainly produced by collagen denaturation. Gelatin obtained from cold-water fish has low sol-gel transition temperatures. Chemical and physical treatments can be used to modify the gelatin network by establishing cross-links between the gelatin chains to improve the properties of the gel. In this study, cross-linking in cold-water fish gelatin-based hydrogels was established by tannic acid (TA) and caffeic acid (CA), each at concentrations of 1, 3 and 5%. The effect of CA and TA concentrations on the physicochemical properties of gelatin hydrogels was investigated. The strength of the gel and the degree of crosslinking increased with increasing the concentration of tannic acid from 1 to 3%, which increased the strength of the gel from 325.00 to 343.62 N/mm² and the degree of crosslinking from 82.01 to 84.99%. At higher levels of tannic acid, a decrease in gel strength and degree of crosslinking was observed 301.90 N/mm² and 75.48%, respectively. However, these properties of hydrogels increased steadily with increasing levels of caffeic acid (p <0.05). The swelling rate also decreased due to the combination of different levels of tannic acid and caffeic acid. The maximum swelling rate for the control was 1732.30% and the minimum swelling rate for 3% tannic acid was 594.79%. The crosslinked gelatins by tannic acid significantly improved the denaturation temperature and their thermal stability was higher than that of caffeic acid. This temperature was 89° C in untreated hydrogels and increased to 94 °C and 98 °C in caffeic acid and tannic acid treated hydrogels, respectively. Scanning electron microscopy images of the hydrogel samples showed that the structure of the hydrogels based on cold-water fish gelatin was spongy. The addition of crosslinking agents only slightly reduced the pore size of the gelatin and had no significant effect.

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Because of antioxidant, antimicrobial, and medical properties, bioactive compounds extracted from plants have grown significantly in the development and trade of functional foods containing food-medicine and dietary supplements.However, the volatility, insolubility in the aqueous matrix, and sensitivity to environmental conditions such as temperature, oxygen, and light limite the use of essential oils. Therefore, this study was conducted to investigate the encapsulation technique as a suitable method to protect the essential oil and increase its efficiency. The main purpose of this study was to produce alginate hydrogels containing Thymus daenensis essential oil (Td-EO) loaded with beta-cyclodextrin. The structural properties and antimicrobial features of alginate hydrogel beads incorporated with Td-EO active ingredients were evaluated. The results of hydrogel analysis showed that the particle size and particle size distribution were less than 180 nm and 0.31, respectively, and the encapsulation efficiency of Td-EO for the hydrogel beads was about 90%. A maximum swelling capacity of ~610.3 % was obtained for alginate beads. FESEM, showed that the particle sizes were in the nanometer range and the particles were homogeneous and spherical shapes. FTIR analysis indicated no significant interaction between essential oil, beta-cyclodextrin and alginate, so alginate hydrogel is a suitable material for encapsulating active compounds. Hydrogels had an inhibitory effect on the growth of two strains of bacteria, S. aureus and E. coli. The release of Td-EO from alginate beads in two short-term and long-term periods were studied. The release rate of bioactive compounds can be reduced by encapsulating in β-cyclodextrin and producing its alginate hydrogel, and thus can be used as a suitable tool to control release in food and pharmaceutical systems.

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Hydrogels are the smart polymeric materials, which undergo large deformation when they are subjected to different physical and chemical stimuli in contact with fluids. These materials can be applied as sensors and actuators for instance in microfluidics in which the fluid-solid interactions have an important effect on its performance. On the other hand, the use of graded materials is also important considering their advantages. In this study, the behavior of a functionally graded temperature sensitive hydrogel micro-valve is investigated through considering the fluid-solid interactions. In this regard, the appropriate numerical tool for finite element modeling of a functionally graded hydrogel micro-valve has been developed that it has been implemented in both non fluid-solid interactions and fluid-solid interactions simulation. The homogeneous cases of the micro-valve have also been considered to distinguish the functionally graded temperature sensitive hydrogel micro-valve effect. The results indicate that the effect of fluid-solid interactions was important and have considerable impact on micro-valve operating parameters particularly its closing temperature and fluid flow rate. Thus, a comprehensive study on hydrogel-based micro-valve has been presented  considering operating parameters such as inlet pressure and cross linking density of hydrogel.

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This study was conducted with the aim of investigating the composite of biodegradable polymers and nanoparticles in hydrogels in the form of a review article. Biodegradable polymer composites with nanoparticles in hydrogels is an advanced research field that combines the accumulation of new technologies in the field of biodegradable polymers and nanomaterials. These composites are created by integrating biodegradable polymers, which decompose naturally and reduce the harmful effects on the environment, with nanoparticles in hydrogels. The presence of nanoparticles in the structure of these composites has improved the mechanical, electrical, and thermal properties and made these compounds as multifunctional materials with wide applications in the fields of food industry, packaging, medicine, environment, and electronics. Hydrogel, as the main matrix of these composites, guarantees the ability of absorbing water and the controlled transfer of active substances. These advances are important not only in the field of science and engineering, but also in making sustainable solutions for future technologies.
 

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Cardiovascular diseases (CVDs) are the most prevalent cause of fatalities worldwide, affecting both cardiac and vascular tissues. Tissue engineering is a promising treatment alternative for people with end-stage CVDs; however, it has disadvantages such as poor scaffold design control and insufficient vascularization. 3D bioprinting, a recent advancement, has overcome these restrictions by creating layer-by-layer structures such as organs, scaffolds, and blood vessels. This method enables precise control over cell distribution, architectural structure, and compositional correction. Furthermore, since cardiac tissue is electroactive, incorporating electroconductive nanomaterials into the scaffold facilitates intracellular communication, mimics the heart's biochemical and biomechanical microenvironment, and prevents arrhythmia in the heart. In addition, these electroconductive materials can improve the quality of 3D-printed scaffolds. In this study, we will review the different techniques of 3D printing hydrogels after evaluating the many types of hydrogels employed for cardiac tissue engineering (CTE). Then, we will discuss the influence of incorporating electroconductive fillers into hydrogels on printed scaffold quality. Finally, we will briefly discuss the challenges and potentials.
 

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There is a growing trend towards healthy meat products containing lower fat content. The use of fat replacers can solve the quality problems of low-fat products. This study aimed to produce low-fat frankfurter sausage using a new fat replacer. Thus, in the first stage, Reconstituted Agar Hydrogel (RAH) was produced by adding water to agar cryogel after homogenization. In the second stage, RAH was used as a fat substitute in frankfurter sausage at 0, 25, 50, 75, and 100%. Then, the characteristics of the resulting low-fat sausage, including chemical composition, water holding capacity, cooking loss, texture characteristics, porosity, color, percentage of fat after frying, oil absorption, pH over time, and sensory evaluation were examined. Results showed that RAH could form two kinds of gel by temperature changes: a low-set gel at 55˚C and a high-set gel at 90˚C. Substitution of oil in the sausages caused an increase in moisture content, porosity, oil absorption, and cooking loss. On the other hand, this replacement reduced fat content, cutting force, water-holding capacity, fat percentage after frying, and texture properties such as hardness, cohesiveness, springiness, gumminess, and chewiness. The results of pH measurements over time showed that sulfated antimicrobial groups in the agar structure delayed the spoilage of sausages containing RAH compared to the control sample. Sensory evaluation showed that RAH-containing sausages were not significantly different from the control sample in terms of color, juiciness, and texture. However, flavor and overall acceptance increased significantly under the influence of this substitution (P< 0.05). Therefore, the consumers selected a sample with 25% replacement as the optimal sample. As a result, RAH can be successfully used as a fat replacer in low-fat products with desirable quality characteristics.