Polyacrylamide-based Hydrogels Research Articles

Optimizing Salt Leakage Mitigation and Comparing Sorption-Desorption Characteristics of Polyacrylamide-Based Hydrogels.

Solid hygroscopic materials are extensively utilized in diverse fields, including adsorption heat transfer, adsorption heat storage, atmospheric water harvesting (AWH), and air conditioning dehumidification. The efficacy and energy efficiency of these materials in practical applications are significantly influenced by their adsorption and desorption properties. Yet, the introduction of inorganic salts to boost adsorption performance can result in issues like salt leakage. In this research, we prepared a polyacrylamide hydrogel through free radical polymerization, and its water-absorbing capabilities were improved by incorporating the hygroscopic salt lithium chloride. We compared it to a salt-based porous adsorbent, AlFum-LiCl, which also exhibited strong water adsorption properties and the potential for large-scale production. While AlFum-LiCl suffered from limited pores and salt leakage during high water uptake, the optimized PAM-LiCl displayed superior water sorption capabilities, showing no salt leakage even at water uptake of up to 3.5 g/g. At 25 °C, PAM-LiCl achieved equilibrium water uptake of 1.26 g/g at 30% RH and 3.15 g/g at 75% RH. In this context, utilizing 20 g of PAM-LiCl for the AWH experiment yielded daily water outputs of 8.34 L/kg at 30% RH and 16.86 L/kg at 75% RH. The salt-optimized PAM-LiCl hydrogel offers the benefit of application in higher relative humidity environments without the risk of deliquescence, underscoring its promise for atmospheric water harvesting.

Designing Starch–Alginate Hydrogels for Controlled Delivery of Fungicide for the Alleviation of Environmental Pollution

In this work, a controlled delivery system for the fungicide thiophanate-methyl (TM) was developed for the alleviation of environmental pollution using starch–alginate–polyacrylamide hydrogels as a sustainable agricultural development approach. The polymer hydrogel was synthesized by grafting poly(acrylamide) onto starch–alginate using N,N-methylenebisacrylamide (NNMBA) as the cross-linker. The copolymers were confirmed by characterization techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared analysis, X-ray diffraction, 13C NMR, TGA-DTG, and differential scanning calorimetry. SEM confirmed the heterogeneity, and AFM showed the rough surface morphology of the copolymeric hydrogels. The thermogravimetric analysis results indicated the increase in the thermal stability of the cross-linked polymers after modification. Evaluation was carried out on the water absorption capacity of the polymer and the release of the encapsulated fungicide. The swelling of the hydrogel decreased with the increment in cross-linking density with a rise in [NNMBA]. It also influenced the diffusion of the fungicide from the encapsulated copolymer, wherein the increase in the cross-linker content decreased the fungicide release from the copolymer. Hydrogels absorbed 18.30 ± 1.40 (g/g of gel) water, indicating the water retention capacity of the hydrogel material which could be useful for plant growth in the arid regions. The release profile followed the non-Fickian diffusion mechanism with a sustained delivery of TM. Water retention and the controlled release properties of the hydrogel indicated its usefulness in sustainable agricultural development and alleviation of environmental pollution caused by the fungicide use. Overall, the formation of a controlled pesticide delivery system based on natural polysaccharides with polyacrylamide-based hydrogels which act as nutrients for plants on degradation is a unique approach, implying that the slow release of the pesticide will reduce environmental pollution and pesticide cost.

Electron Microscopy of Cells Grown on Polyacrylamide Hydrogels.

The composition of the cell culture environment profoundly affects cultured cells. Standard cell culture equipment such as plastic and glass provide extremely stiff surfaces compared to physiological cell environments (i.e., tissue). A growing body of evidence documents the artificial behavior and morphology of cells cultured on supraphysiologically stiff surfaces, such as glass (elastic modulus ca. 70,000 MPA) or plastic (e.g., polystyrol ca. 3300 MPA). Therefore, polymer-based hydrogels are increasingly employed as more physiologically appropriate (<100 kPA) supports for 2D or 3D culture. Since multiple properties that influence the cultured cells may be easily adjusted, hydrogels have become versatile tools for studying cells in a more native in vitro environment. Polyacrylamide-based hydrogels can be used as culture substrates for a broad variety of adherent cells and are easy to handle in most downstream biological assays, such as immunohistochemistry or molecular biology methods. We faced, however, serious difficulties with processing high stiffness polyacrylamide-based hydrogels for electron microscopy. To overcome this problem, we developed a simple protocol for embedding and processing cells grown on high stiffness polyacrylamide hydrogels that do not require modifications of routine embedding protocols. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Embedding of polyacrylamide-based hydrogels for transmission electron microscopy Alternate Protocol 1: Procedure for detached hydrogels Alternate Protocol 2: Procedure for attached hydrogels.

Antifouling and antimicrobial cobaltocenium-containing metallopolymer double-network hydrogels.

ABSTRACTCompared with single-network hydrogels, double-network hydrogels offer higher mechanical strength and toughness. Integrating useful functions into double-network hydrogels can expand the portfolios of the hydrogels. We report the preparation of double-network metallopolymer hydrogels with remarkable hydration, antifouling, and antimicrobial properties. These cationic hydrogels are composed of a first network of cationic cobaltocenium polyelectrolytes and a second network of polyacrylamide, all prepared via radical polymerization. Antibiotics were further installed into the hydrogels via ion-complexation with metal cations. These hydrogels exhibited significantly enhanced hydration, compared with polyacrylamide-based hydrogels, while featuring robust mechanical strength. Cationic metallopolymer hydrogels exhibited strong antifouling against oppositely charged proteins. These antibiotic-loaded hydrogels demonstrated a synergistic effect on the inhibition of bacterial growth and antifouling of bacteria, as a result of the unique ion complexation of cobaltocenium cations.

Cefuroxime-Loaded Hydrogels for Prevention and Treatment of Bacterial Contamination of Open Wounds

Dextran/Sulfodextran-graft-polyacrylamide- and polyacrylamide-based hydrogels were synthesized by radical polymerization and loaded with cefuroxime to obtain antimicrobial wound dressings. Antibiotic release from the antibiotic-loaded hydrogels into an aqueous solution was studied by the HPLC-UV method. It is shown that cefuroxime-loaded Dextran/Sulfodextran-graft-polyacrylamide hydrogels release the antibiotic more slowly compared to polyacrylamide hydrogel with the same density of cross-links. Antibacterial activity of the synthesized materials was tested in vitro against wild strains of S. aureus, E. coli, and Klebsiella spp. The possibility of using the obtained antimicrobial hydrogels for the treatment of infected wounds was confirmed in vivo in a rat model.

Application of polyacrylamide-based hydrogels for water removal from biodiesel in isothermal experiments

Fuels with water contents higher than the limits specified by regulatory agencies may be subjected to high turbidity, microbial growth fouling, sludge formation, and promote the corrosion and failure of fuel injection components. In this investigation, polyacrylamide, poly(acrylamide-co-sodium acrylate) and poly(acrylamide-co-acrylic acid) hydrogels were used to adsorb water from biodiesel in a batch system at 20 °C. The water content of biodiesel samples saturated with water could be lowered down to near 400 mg of water/kg of biodiesel under equilibrium conditions, a value comparable to other more mature technologies and in accordance with the EN 14214 standard. Among the three adsorption isotherm models fitted to the experimental data, the Freundlich model presented the best fit for polyacrylamide and poly(acrylamide-co-sodium acrylate) hydrogels, but all models failed for the poly(acrylamide-co-acrylic acid) hydrogel. The use of hydrogels for removal of water from fuels can be easily scaled up to a continuous process for commercial applications.

The New Approach to the Preparation of Polyacrylamide-Based Hydrogels: Initiation of Polymerization of Acrylamide with 1,3-Dimethylimidazolium (Phosphonooxy-)Oligosulphanide under Drying Aqueous Solutions.

The new initiator of the polymerization of acrylamide, leading to the formation of crosslinked polyacrylamide, was discovered. The structure of the synthesized polyacrylamide was characterized by XRD, 1H NMR, and 13C NMR spectroscopy. It was shown that 1,3-dimethylimidazolium (phosphonooxy-)oligosulphanide is able to initiate radical polymerization under drying aqueous solutions of acrylamide, even at room temperature. According to XRF data, the synthesized polyacrylamide gel contains 0.28 wt% of sulphur. The formed polymer network has a low crosslinking density and a high equilibrium degree of swelling. The swelling rate of polyacrylamide gel in water corresponds to the first order kinetic equation with the rate constant 6.2 × 10−2 min−1. The initiator is promising for combining acrylamide polymerization with the processes of gel molding and drying.

High-Strength, Strongly Bonded Nanocomposite Hydrogels for Cartilage Repair

Polyacrylamide-based hydrogels are widely used as potential candidates for cartilage replacement. However, their bioapplicability is sternly hampered due to their limited mechanical strength and puncture resistance. In the present work, the strength of polyacrylamide (PAM) hydrogels was increased using titanium oxide (TiO2) and carbon nanotubes (CNTs) separately and a combination of TiO2 with CNTs in a PAM matrix, which was interlinked by the bonding between nanoparticles and polymers with the deployment of density functional theory (DFT) approach. The synergistic effect and strong interfacial bonding of TiO2 and CNT nanoparticles with PAM are attributed to high compressive strength, elastic modulus (>0.43 and 2.340 MPa, respectively), and puncture resistance (estimated using the needle insertion test) for the PAM-TiO2-CNT hydrogel. The PAM-TiO2-CNT composite hydrogel revealed a significant self-healing phenomenon along with a sign toward the bioactivity and cytocompatibility by forming the apatite crystals in simulated body fluid as well as showing a cell viability of ∼99%, respectively. Furthermore, for new insights on interfacial bonding and structural and electronic features involved in the hydrogels, DFT was used. The PAM-TiO2-CNT composite model, constructed by two interfaces (PAM-TiO2 and PAM-CNT), was stabilized by H-bonding and van der Waals-type interactions. Employing the NCI plot, HOMO-LUMO gap, and natural population analysis tools, the PAM-TiO2-CNT composite has been found to be most stable. Therefore, the prepared polyacrylamide hydrogels in combination with the TiO2 and CNT can be a remarkable nanocomposite hydrogel for cartilage repair applications.

Hydrolyzed Hydrogels with Super Stretchability, High Strength, and Fast Self-Recovery for Flexible Sensors.

Polyacrylamide is widely employed in constructing functional hydrogels. However, the volume expansion of this hydrogel in water weakens its mechanical properties and restricts its application. Herein, we report a strategy to convert the swollen and weak polyacrylamide/carboxymethyl chitosan hydrogel into a strong and tough one by hydrolysis in acid solution with an elevated temperature. The obtained hydrolyzed hydrogels possess a high strength, toughness, and tearing fracture energy of 5.9 MPa, 22 MJ/m3 and 7517 J/m2, which are 254, 535 and 186 times higher than those of the original swollen one, respectively. In addition, the gels demonstrate low residual strain and rapid self-recovery abilities. Moreover, the gels have good shape memory behavior controlled by temperature. Furthermore, the gels can be worked as strain sensors with a broad strain window, high sensitivity, excellent linear response, and great durability in monitoring human motions after immersing treatment in a normal saline solution. This work provides a new method for preparing the stretchable and tough polyacrylamide-based hydrogels used in the areas of soft actuators and flexible electronics.

Evaluating Poly(Acrylamide-co-Acrylic Acid) Hydrogels Stress Relaxation to Direct the Osteogenic Differentiation of Mesenchymal Stem Cells.

The aim of this study is to investigate polyacrylamide-based hydrogels stress relaxation and the subsequent impact on the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Different hydrogels are synthesized by varying the amount of cross-linker and the ratio between the monomers (acrylamide and acrylic acid), and characterized by compression tests. It has been found that hydrogels containing 18% of acrylic acid exhibit an average relaxation of 70%, while pure polyacrylamide gels show an average relaxation of 15%. Subsequently, hMSCs are cultured on two different hydrogels functionalized with a mimetic peptide of the bone morphogenetic protein-2 to enable cell adhesion and favor their osteogenic differentiation. Phalloidin staining shows that for a constant stiffness of 55kPa, a hydrogel with a low relaxation (15%) leads to star-shaped cells, which is typical of osteocytes, while a hydrogel with a high relaxation (70%) presents cells with a polygonal shape characteristic of osteoblasts. Immunofluorescence labeling of E11, strongly expressed in early osteocytes, also shows a dramatically higher expression for cells cultured on the hydrogel with low relaxation (15%). These results clearly demonstrate that, by fine-tuning hydrogels stress relaxation, hMSCs differentiation can be directed toward osteoblasts, and even osteocytes, which is particularly rare in vitro.

The Effect of Hydrogel on Plant Growth

One of the problems of growing seedlings at home is that the garden land is infected with pathogenic organisms. A hydrogel is a water-absorbing polymer in the form of granules, which has a unique ability. It can absorb and retain up to 1 liter of water per 10 g of hydrogel when swollen. The most well-known are polyacrylamide-based hydrogels. When the hydrogel is in a dry state, the polymer chains are in a folded state, when water is added, they diverge and water penetrates inside. The granules swell with the formation of a hydrogel. Hydrogels are essentially made on the basis of environmentally friendly polymers. It is non-toxic, retains all its original properties at different (low and high) temperatures in the soil for five years. Therefore, the main goal of my work is to study the effect of hydrogel on plant growth. Tasks of this work: 1) To study the peculiarities of growing plants in hydrogel. 2) Determine the moment of plant life at which it is better to use hydrogel for them 3) Consider the possibility of growing indoor crops in hydrogel.

Lignin-carbohydrate complexes from coconut (Cocos nucifera) coir: Fractionation, structural elucidation, and potential applications

Coconut coir, a major type of tropical lignocellulosic waste, has been restricted from higher-value applications due to its chemical complexity and inherent variability. To better disclose the chemical relationships between polysaccharides and lignin in coir and further exploit its high value-added bio-based materials, two lignin-carbohydrate complexes (LCCs) designated as glucan-lignin (GL) and xylan-lignin (XL) were successively isolated from coir via a simplified and quantitative fractionation method. The characterization of chemical composition, molecular weight distribution, and constituent substructures of the isolated LCC fractions were examined, and the lignin-carbohydrate (LC) chemical linkages were revealed as γ-esters by a 2D heteronuclear singular quantum correlation (HSQC) NMR technique. Furthermore, XL was demonstrated as a more competitive candidate than GL for 2,2-diphenyl-1-picryl-hydrazyl (DPPH) removal in comparison with 2,6-di-tert-butyl-4-methylphenol (BHT, a commercial antioxidant), and was also featured as a more promising reinforcing agent for elevating the adsorption property of polyacrylamide-based hydrogels via the synergistic effect of physical and hydrogen bonding adsorptions.

Biocompatible In Situ Polymerization of Multipurpose Polyacrylamide-Based Hydrogels on Skin via Silver Ion Catalyzation.

Free radical polymerization is a mature method and can be used for preparing multifunctional hydrogels by simply changing the commercial monomers, but the harsh and time-consuming initiation conditions restrict its injectable ability, which further limits its application in the biomedical field. Though some catalysts can be used to accelerate the polymerization, their application is restrained by the biotoxicity. Hence, finding a biocompatible catalyzer for in situ free radical polymerization of hydrogels has a great prospect in biomedical application but is still challenging. In this study, we discovered that silver ions could catalyze free radical polymerization under ambient by transforming hydrone into hydroxyl radicals in the presence of ammonium persulfate, and the in situ-formed hydrogels prepared by this way showed great histocompatibility, hemocompatibility, cytocompatibility, and immunocompatibility. Benefitting from its convenience and biocompatibility, the in situ polymerization of polyacrylamide-based hydrogels for tissue adhesion, wound dressing, and conductive materials on the skin could be realized by simply blending diverse ingredients. Furthermore, this discovery may be a step toward the in situ-polymerized hydrogels for biomedical applications.

A comprehensive review of in situ polymer hydrogels for conformance control of oil reservoirs

In fractured reservoirs, fluids injected Enhanced Oil Recovery (EOR) are channeled through the fracture zones and travel through highly permeable regions, failing to displace part of the oil, and decreasing oil recovery efficiency. To solve these problems, the conformance control technique is now widely used, as it allows the reservoir to be swept totally, similar to the ideal condition. In this context, polyacrylamide-based polymer gel systems can be used to block the high-permeability regions of the rock matrix, forming in situ hydrogels that block the rock pores, avoiding the channeling of the fluids, and increasing the oil production. These polyacrylamide-based hydrogels can be crosslinked by inorganic (metal ions) or organic substances, and various systems are used for conformance control. Due to the greater stability of the bond formed between the polymer and the organic crosslinker, these systems are now used in higher temperature reservoirs. In order to produce hydrogels with higher resistance to severe salinity and temperature conditions, nanoparticles are applied to form systems with good mechanical resistance, and high thermal stability. These have presented promising results for conformance control.

Rheology and adhesive properties versus structure of poly(acrylamide-co-hydroxyethyl methacrylate) hydrogels

This study investigates the relationship between structure, rheological properties and adhesive performances of poly(acrylamide-co-hydroxyethyl methacrylate) P(AM-HEMA) hydrogels. The microstructure and, as a consequence the rheological behavior, of polyacrylamide-based hydrogels have been modulated by varying the precursory reaction mixtures composition. Elastic G′ and loss G″ shear moduli measurements highlighted their inhomogeneous structure. Structural parameter values predicted by the rubber elasticity theory showed that P(AM-HEMA) networks are constituted by dense polymer regions interconnected by more dilute polymer ones as a result of multiple cross-linking reactions. We demonstrated that increasing the cross-linker composition allows to increase G′ values however the inhomogeneity degree of the networks is higher. Contrarily, HEMA introduction into the feed and the increase of monomers’ composition suppress the extent of PAM network inhomogeneity. Probe test tack experiments evidenced the effect of P(AM-HEMA) structure on the rheological properties and adhesion energy as well as the detachment type.

Physical and Chemical Characterisation of Acrylamide-Based Hydrogels, Aam, Aam/NaCMC and Aam/NaCMC/MgO

To find out the best structure of acrylamide-based hydrogels, three different composites are synthesized and characterized. Polyacrylamide-based hydrogels were obtained by chemical crosslinking of MBA using acrylamide, sodium carboxymethylecellulose (NaCMC), N,N,N′,N′-tetramethylethylenediamine (TEMED) and ammonium persulfate (APS) as the initiators. The interest in MgO nanoparticles is not only due to their stability under harsh process conditions but also for human health, where they are known to be necessary minerals. It is expected that the structure of the hydrogels can be affected positively by using MgO as a nanoparticle in their composite. To control the initial burst release through modification of the structure of the matrix, the MgO nanoparticles are applied. These nanoparticles can affect the release mechanism. In the current research, FESEM, NMR, DTA/TGA and DSC are studied for the structure of polymers. In the FESEM, existing MgO inside the hydrogel system brings about a shift in the porosity of hydrogels. The 1H NMR spectrum of polymers showed characteristic proton peaks at 4.6 and 4.7, 6.1 and 6.2 ppm. An endothermic peak indicating loss of weakly bound water molecules from the hydrogel network is shown in DTA curves of hydrogels at around 80 °C. An exothermic peak at around 270 °C for Aam and Aam/NaCMC hydrogels and also a peak at 360 °C in Aam and Aam/NaCMC hydrogels and 320 °C for Aam/NaCMC/MgO is shown. The DSC profiles of the hydrogels show that water has a higher evaporation temperature in the polyacrylamide hydrogel (84 °C).The largest depression of the temperature was observed on the Aam/NaCMC/MgO hydrogel (∆T = 94 °C), which confirmed the higher hydrophilicity of Aam/NaCMC/MgO as compared to pure Aam hydrogel and Aam/NaCMC hydrogel.

Acrylamide-based hydrogel drug delivery systems: Release of Acyclovir from MgO nanocomposite hydrogel

Polyacrylamide-based hydrogels were obtained by chemical crosslinking of MBA using acrylamide, sodium carboxymethylecellulose (NaCMC), N, N, N’, N’-tetramethylethylenediamine (TEMED) and ammonium persulfate (APS) as the initiators. The interest on MgO nanoparticle is not only due to their stability under harsh process conditions but also for human health, where they are known to be necessary minerals. The systems were characterized with regard to the rheology behavior of hydrogel, degree of crosslinking the polymers, Fourier Transform Infrared Spectroscopy (FTIR), and Field Emission Scanning Electron Microscope (FESEM). The dispersion of the nanoparticles (MgO) and drug (Acyclovir) inside the hydrogel was shown by TEM. Acyclovir, that is one of the famous drugs to treat the vaginal infections, was loaded in the polymer through the soaking method in an aqueous solution including the drug for drug delivery and release in the vaginal. The physical and chemical characterizations of the fortified hydrogels provided an assessed report on the morphological structure of the polymer, swelling behavior, bonding formation of gels and physical properties. To study the drug release in two different mediums, PBS and SVF aqueous solutions were utilized. To determine the amount of released drug from the hydrogels, HPLC was used. The pH sensitivity and the in vitro drug release of hydrogels in three different pH (pH 4,6,8) was studied. The objectives of this present study are to characterize the MgO nanocomposite hydrogel and to study the effect of different buffers on the release of Acyclovir from hydrogels.

One-step synthesis of self-healable hydrogels by the spontaneous phase separation of linear multi-block copolymers during the emulsion copolymerization

Self-healable polyacrylamide-based hydrogels were prepared at room temperature via a one-step emulsion copolymerization of acrylamide (AM), dodecyl 2-methacrylate (DM), and 5-acetylaminopentyl acrylate (AAPA) using sodium dodecyl sulfonate (SDS) as the emulsifier and ammonium persulfate (APS) as the initiator. The produced linear multi-block copolymer chains are composed of randomly-linked hydrophilic polyacrylamide segments (PAM) and hydrophobic segments constituted by DM and AAPA units (P(DM-co-AAPA)). The P(DM-co-AAPA) segments will self-aggregate into hydrophobic microdomains during the polymerization process driven by the hydrophobic interactions, and finally separate from water phase, acting as the crosslinks and leading to the formation of strong hydrogels with a storage modulus as high as 400Pa. These hydrophobic microdomains will be dissolved in water when the temperature increases to 70°C, resulting in a temperature-responsive reversible sol-gel transition of the prepared hydrogels. Furthermore, the prepared hydrogels have excellent self-healing ability. The broken hydrogels can be automatically healed into a body with a same strength within 2-min’s contact. This work provides a new simple way to prepare reversible physical crosslinked hydrogel with high strength and self-healing efficiency.

Cytocompatible, Photoreversible, and Self-Healing Hydrogels for Regulating Bone Marrow Stromal Cell Differentiation.

Photo-crosslinking and self-healing have received considerable attention for the design of intelligent materials. A novel photostimulated, self-healing, and cytocompatible hydrogel system is reported. A coumarin methacrylate crosslinker is synthesized to modify the polyacrylamide-based hydrogels. With the [2+2] cyclo-addition of coumarin moieties, the hydrogels exhibit excellent self-healing capacity when they are exposed to light with wavelengths at 280 and 365 nm, respectively. To enhance cell compatibility, a poly (amidoamine) crosslinker is also synthesized. Variations in light exposure times and irradiation wavelengths are found to alter the self-healing property of the hydrogels. The hydrogels are shown to induce a regular cellular pattern. The hydrogels are used to regulate bone marrow stromal cells differentiation. The relative mRNA expressions are recorded to monitor the osteogenic differentiation of the cells.

Ni ferrite highly organized as humidity sensors

Synthesis and characterization of nickel ferrite using polyacrylamide-based hydrogels as template agents for obtaining NiFe2O4 by the sol–gel autocombustion method was studied, the investigation representing a novelty in the field.The polyacrylamide-based hydrogel used as a template agent, was synthesized by an original simultaneous polymerization-crosslinking method, using a monofunctional crosslinking agent. The ferrite was synthesized by the sol–gel autocombustion method, using citric acid as a chelating/fuel agent. The as-obtained hydrogel was characterized by IR, SEM and thermogravimetric techniques, as well as swelling behavior. As-synthesized ferrites were characterized by IR, SEM, XRD techniques, as well as by electrical and magnetic properties. The electrical investigations were carried out in different humidity conditions in order to highlight the influence of humidity on electrical properties, in this respect the prepared NiFe2O4 with highly organized structure was tested for applications as humidity sensors.