Hydrogels In Aqueous Solutions Research Articles

Carbon Dot-Stabilized Hydrogel Composite: A New Adsorbent for Efficient and Sustainable Pb(II) Removal.

In this paper, a carbon dot hydrogel composite (CDs-Hy) capable of efficiently removing Pb(II) was prepared by hydrogen bonding self-assembly in combination with carbon dots and a hydrogel. CDs-Hy was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), and the effect of the adsorption conditions on the adsorption efficiency of CDs-Hy was studied. The results of the study showed that the incorporation of carbon dots, on the one hand, significantly increased the adsorption capacity of the material. On the other hand, it can increase the stability of hydrogels in aqueous solution. The possible adsorption mechanisms were further verified as ion exchange and coordination. CDs-Hy is a novel adsorbent material capable of removing Pb2+ efficiently, which can be reused several times with high stability.

Thermo-tunable Injectable Thermosensitive Hydrogel and its Application as Protein Carriers

It is known that polymer chemistries determine mechanical and physical properties of hydrogels and thus its drug delivery performance. In order to achieve desired drug release behavior, triblock copolyester PCT-PEG-PCT with proper hydrogel formulation has to be synthesized. This research has demonstrated a way to adjust hydrogel mechanical and gelation properties by simply physically mixing amphiphilic copolymers with different composition to achieve desired protein carriers. Tri-block copolymer poly (CL-co-TOSUO)-PEG-poly (CL-co-TOSUO), briefed as (PCT-PEG-PCT) with different composition have been successfully synthesized. These copolymers are thermosensitive and can form hydrogels in aqueous solution. Copolymers with higher percentage hydrophobic PCT blocks show higher mechanical stiffness and yet lower solubility. To reduce the crystallinity of the hydrophobic block and soften the hydrogel, the copolymer with long PCT blocks was physically mixed with ones with shorter PCT blocks. The polymer mixture demonstrated a moderated mechanical stiffness and desired solubility. The polymer mixture also achieved a gelation temperature at 37°C, which is desirable for drug delivery. Macromolecular drug, bovine serum albumin (BSA) was used as model drug for its release study. This protein drug was successfully loaded into the polymer mixture, and the drug release study shows the polymer mixture is able to extend a stable drug release for over 48 hours. This result confirms physical mixing of PCT-PET-PCT thermosensitive copolymers can tune gel properties and improve drug delivery performance without redesigning and synthesizing new polymers.

Non-swelling, super-tough, self-healing, and multi-responsive hydrogels based on micellar crosslinking for smart switch and shape memory

Non-swelling super-tough polymer hydrogels have great potentials for stable applications in wet conditions. It has been challenging since most polymer hydrogels uptake water from the environment and swell, which deteriorates the mechanical strength and toughness. Here, we present multi-responsive non-swelling polymer hydrogels (PHFGs) by using amphiphilic triblock copolymer micelles as non-covalent crosslinkers. Pluronic F127 (or polyethylene oxide-block-polypropylene oxide-block-polyethylene oxide, PEO-PPO-PEO) (F-127) micelles are used as a prototype for the synthesis of micelle-crosslinked poly-(2-hydroxyethylene methacrylate) (PHEMA) hydrogels, without using any modification of F-127 or other crosslinkers. FT-IR and 1H NMR studies provide first evidence that F-127 micelles form extensive hydrogen bonding and hydrophobic association with PHEMA chains. The non-covalent crosslinked hydrogels show a high fracture elongation about 460 %, a fracture strength about 240 kPa, and a fracture toughness about 660 kJ/m3. Negligible swelling is observed for the polymer hydrogels in aqueous solutions. The hydrogels are self-healable, and responsive to variations in pH or water content to change volume, shape, and transparency. Such multiple-responsive polymer hydrogels are utilized as smart switches and shape memory materials that are actuated by environmental stimuli in a controllable manner.

Rapid Removal of Acid Red 88 by Zeolite/Chitosan Hydrogel in Aqueous Solution

In the present study, we developed a new adsorbent product with zeolite crosslinked chitosan (ZL–CH hydrogel) to remove acid red 88 (AR88) in an aqueous solution. The effects of several factors, such as the comparison of ZL–CH hydrogel and the absence of chitosan, pH, adsorbent dosage, initial AR88 concentration, contact time, and ion strength, were determined. Obtained results showed that ZL–CH hydrogel improved AR88 removal compared to the absence of chitosan, with an adsorption capacity of 332.48 mg/g in equilibrium time of 1 min, and adding ionic strength had no significant effect. However, with optimal conditions at pH 2.0, dry ZL–CH became hydrogel due to protonation of amino and hydroxyl groups through hydrogen bonds in the AR88 solution. Volume fraction and interaction force decreased with increasing porosity, leading to an increase in adsorption capacity and swelling ratio. Experimental data of the adsorption process showed the Freundlich isotherm model. The equilibrium for adsorption and swelling kinetics studies showed and fitted a pseudo-second-order model. NaOH was successful as a desorbing agent with 93.8%, and it followed the pseudo-second-order kinetics model. The recycling process indicates great potential for AR88 removal.

Adsorption Behavior of Methylene Blue Dye by Novel CrossLinked O-CM-Chitosan Hydrogel in Aqueous Solution: Kinetics, Isotherm and Thermodynamics.

The chemical cross-linking of carboxymethyl chitosan (O-CM-chitosan), as a method for its modification, was performed using trimellitic anhydride isothiocyanate to obtain novel cross-linked O-CM-chitosan hydrogel. Its structure was proven using FTIR, XRD and SEM. Its adsorption capacity for the removal of Methylene Blue (MB) dye from aqueous solution was studied. The effects of different factors on the adsorption process, such as the pH, temperature and concentration of the dye, in addition to applications of the kinetic studies of the adsorption process, adsorption isotherm and thermodynamic parameters, were studied. It was found that the amount of adsorbed MB dye increases with increasing temperature. A significant increase was obtained in the adsorption capacities and removal percentage of MB dye with increasing pH values. An increase in the initial dye concentration increases the adsorption capacities, and decreases the removal percentage. It was found that the pseudo-second-order mechanism is predominant, and the overall rate of the dye adsorption process appears to be controlled by more than one step. The Langmuir model showed high applicability for the adsorption of MB dye onto O-CM-chitosan hydrogel. The value of the activation energy (Ea) is 27.15 kJ mol−1 and the thermodynamic parameters were evaluated. The regeneration and reuse of the investigated adsorbent was investigated.

In Situ Preparation of Mechanically Enhanced Hydrogel via Dispersion Polymerization in Aqueous Solution.

Hydrogels with improved mechanical properties can expand to a greater range of applications. The fabrication of conventional toughened hydrogels typically requires precise modifications, multiple components, and complex steps. Here, a straightforward "one-step" polymerization method for the in situ preparation of hydrogels in aqueous solutions, is reported. Inspired by polymerization-induced self-assembly (PISA), water-miscible monomers are copolymerized during the hydrogel fabrication; the growing blocks eventually form physical bridges thus providing a mechanism for effective energy dissipation. The rheological and mechanical properties are evaluated and the results reveal that this strategy can be an effective approach to design mechanically enhanced hydrogels for a wide range of applications.

β-Cyclodextrin/Triclosan Complex-Grafted Methacrylated Glycol Chitosan Hydorgel by Photocrosslinking via Visible Light Irradiation for a Tissue Bio-Adhesive.

Accelerating wound healing with minimized bacterial infection has become a topic of interest in the development of the new generation of tissue bio-adhesives. In this study, we fabricated a hydrogel system (MGC-g-CD-ic-TCS) consisting of triclosan (TCS)-complexed beta-cyclodextrin (β-CD)-conjugated methacrylated glycol chitosan (MGC) as an antibacterial tissue adhesive. Proton nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC) results showed the inclusion complex formation between MGC-g-CD and TCS. The increase of storage modulus (G’) of MGC-g-CD-ic-TCS after visible light irradiation for 200 s indicated its hydrogelation. The swollen hydrogel in aqueous solution resulted in two release behaviors of an initial burst and sustained release. Importantly, in vitro and in vivo results indicated that MGC-g-CD-ic-TCS inhibited bacterial infection and improved wound healing, suggesting its high potential application as an antibacterial tissue bio-adhesive.

Water-absorbing materials based on polymer hydrogel and bentonite

The article deals with the production, sorption and rheological properties of composite materials based on polymer hydrogel and bentonite. It is shown that bentonite prevents the collapse of the hydrogel in aqueous solutions of electrolytes and leads to an increase in the moisture content after the collapse. After several repeated cycles of swelling in water, followed by drying at 60 and 110 °C, the degree of swelling of the composite is higher than that of the hydrogel. In the temperature range from 20 to 40 °C, the polymer hydrogel and the composite are able to withstand at least ten cycles of swelling and drying without changing the degree of swelling.

Drug Delivery Through Multifunctional Polypeptidic Hydrogels.

Over the last two decades, remarkable progress has been made to the discovery of novel drugs as well as their delivery systems for the treatment of cancer, the major challenge in medicine. Pharmaceutical scientists are trying to shift from traditional to novel drug delivery systems by applying nanotechnology and, in particular, polymeric carriers to medicine. In complex diseases, very sophisticated nanocarriers should be designed to encapsulate a significant quantity of drugs and bypass biological barriers with minimum cargo loss to effectively and directly deliver the encapsulated drug to the desired pathological site. One of the most promising classes of polymeric materials for drug delivery applications is polypeptides, combining the properties of the traditional polymers with the 3D structure of natural proteins, i.e., a-helices and β-sheets. In this chapter, we present the recent progress in the synthesis of polymers that form hydrogels in aqueous solutions, based on polypeptides prepared through ring-opening polymerization of N-carboxy anhydrides and which have been loaded with anticancer drugs and studied for their functionality. Advancements in drug design and improvement of multifunctional nanocarriers from the combination of well-defined macromolecular architectures and smart materials are the future for the successful treatment of numerous lethal diseases.

Swelling behavior of acrylamide and sodium acrylate copolymer hydrogel in aqueous solutions of copper (II) chloride with amino acids additives

Swelling of acrylamide and sodium acrylate copolymer polyelectrolyte hydrogel in aqueous Cu(II) chloride solutions with additives of proteinogenic amino acids glycine and L-histidine has been studied. Research relevance is due to the application of such systems in agrochemical products that are supposed to have high water absorption capacity in the presence of microelements ions and amino acids, which are used to prevent nutritional deficiency and make plants resistant to adverse weather conditions and diseases. Gravimetry, atomic absorption spectrometry, FTIR ATR spectroscopy and molecular absorption spectrophotometry were used. The impact of acidity (pH 3, 5 and 7) of aqueous Cu(II) chloride solutions with amino acids additives on the hydrogel swelling degree and Cu(II) ions absorption has been determined. The reasons for changes in the hydrogel swelling degree in aqueous Cu(II) chloride solutions in presence of glycine and L-histidine have been found. The main product of the crosslinked copolymer interaction with the components of 0.01 M aqueous Cu(II) chloride solution with the addition of 0.04 M glycine or L-histidine at pH 3 has been assumed to be a mixed Cu(II) ions complex with functional groups of both copolymer and amino acids.

Swelling of polyacrylamide-based hydrogel in aqueous solutions of low-molecular salts

The swelling kinetics of cross-linked polyacrylamide was studied depending on the composition of the external solution. It was shown that the polymer gel swelling during the transition from water to a potassium or sodium chloride solution and vice versa sharply decreases, then gradually increases. The swelling of gel in a solution of sodium chloride is higher than that of potassium chloride. In the equilibrium swollen gel, the concentration of salts in the gel phase is higher than in the external solution and increases with the transition from potassium chloride to sodium chloride.

6-acylamino nicotinic acid-based hydrogelators applicable in phase selective gelation, reproducible mat formation and toxic dye removal

Formation of nanofibers and nanovesicles in the self-assembled state of small amphiphilic molecules has applications in versatile fields such as tissue engineering, controlled delivery of drug molecules, etc. This paper demonstrated the self-aggregation behavior of three synthesized 6-acylamino nicotinic acid amphiphiles named 6-octanoylamino-nicotinic acid (OANA), 6-decanoylamino-nicotinic acid (DANA) and 6-dodecanoylamino-nicotinic acid (DDANA) in water and basic aqueous solution. The result showed that the amphiphiles successfully self-organize into vesicles and twisted ribbons in water. FT-IR study revealed existence of mixtures of handedness in the fibrous structures. CD spectroscopy and TEM study elucidated formation of chiral structures through aggregation. Results showed that DDANA forms thermoreversible hydrogel in aqueous solutions of NaOH and Na2CO3, whereas other two amphiphiles form hydrogel only in the presence of NaOH. Morphological investigation revealed that the hydrogel is formed due to self-assembly of fibrils of micron length. The elastic fibrillar networks are quite stable to external forces. Existence of bilayer columnar square packing arrangement in the self-assembled state was recognized by XRD measurement. Spectroscopy and theoretical studies established that hydrogen bonding interactions are responsible to self-assemble the amphiphilic molecules. The amphiphiles are efficient phase selective gelators of mineral oils in water–mineral oil mixtures and excellent remover of rhodamine 6G, eosin Y and rose bengal from water. The amphiphiles successfully create reproducible fiber mat applicable in tissue engineering field.

Enhanced adsorption for the removal of antibiotics by carbon nanotubes/graphene oxide/sodium alginate triple-network nanocomposite hydrogels in aqueous solutions.

Large-scale abuse of antibiotics has led to serious environmental problems. Some conventional adsorbents such as several biopolymer gels have poor adsorption performance and inadequate mechanical properties. In this paper, carbon nanotubes (CNTs) and graphene oxide (GO), were combined with sodium alginate (SA) to improve the adsorption performance and other properties of traditional adsorbents. With the help of hydrogen peroxide and l-cysteine (L-cys), carbon nanotubes/l-cysteine@graphene oxide/sodium alginate (CNTs/L-cys@GO/SA) triple-network composite hydrogels were prepared. Compared with traditional hydrogels and the double-network hydrogels that are currently being developed, these triple-network composite hydrogels can exploit their three-dimensional structure to improve their adsorption capacity. The independent triple-network structure increases the three-dimensional space, so there are more pores and pollutant adsorption sites to achieve the high-efficient removal of ciprofloxacin. And the adsorption capacity of CNTs/L-cys@GO/SA hydrogels can reach 181 mg g-1 and 200 mg g-1 at 25 °C and 15 °C respectively in weak acidity environment. In fact, CNTs/L-cys@GO/SA hydrogels show better property at low temperature. In addition, the thermal stability, mechanical properties and swelling ability of the triple-network hydrogels have also been improved. The independent multilayer network can retain the excellent properties of the original materials and make the internal space of hydrogels larger. These multinetwork hydrogels have great potential for removing pollutants from wastewater. In addition, the CNTs/L-cys@GO/SA hydrogels show the higher adsorption capacity of ciprofloxacin under the conditions of weak acidity, low temperature and low inorganic salt concentration, so the removal of ciprofloxacin by hydrogels can also be promoted by changing environmental conditions.

Aqueous Nanoclusters Govern Ion Partitioning in Dense Polymer Membranes.

The uptake and sorption of charged molecules by responsive polymer membranes and hydrogels in aqueous solutions is of key importance for the development of soft functional materials. Here, we investigate the partitioning of simple monatomic (Na+, K+, Cs+, Cl–, I–) and one molecular ion (4-nitrophenolate; NP–) within a dense, electroneutral poly(N-isopropylacrylamide) membrane using explicit-water molecular dynamics simulations. Inside the predominantly hydrophobic environment, water distributes in a network of polydisperse water nanoclusters. The average cluster size determines the mean electrostatic self-energy of the simple ions, which preferably reside deeply inside them; we therefore find substantially larger partition ratios K ≃10–1 than expected from a simple Born picture using a uniform dielectric constant. Despite their irregular shapes, we observe that the water clusters possess a universal negative electrostatic potential with respect to their surroundings, as is known for aqueous liquid–vapor interfaces. This potential, which we find concealed in cases of symmetric monatomic salts, can dramatically impact the transfer free energies of larger charged molecules because of their weak hydration and increased affinity to interfaces. Consequently, and in stark contrast to the simple ions, the molecular ion NP– can have a partition ratio much larger than unity, K ≃10–30 (depending on the cation type) or even 103 in excess of monovalent salt, which explains recent observations of enhanced reaction kinetics of NP– reduction catalyzed within dense polymer networks. These results also suggest that ionizing a molecule can even enhance the partitioning in a collapsed, rather hydrophobic gel, which strongly challenges the traditional simplistic reasoning.

Gelation in solutions of low deacetylated chitosan initiated by high shear stresses

A new process of mechanically initiated formation of chitosan physical hydrogels in aqueous solution, without a cross-linking agent, was studied. Physical hydrogel is formed by mechanical activation of solutions of chitosan with a low deacetylation degree (58%) in situ in a rotor-stator device for 10 s. The formation of 3D gel structure has been proven by rotational viscometry and dynamic rheometry methods. Gelation is caused by the action of high shear stresses initiating the formation of hydrophobic associates from residual chitinous blocks. In comparison with the films from untreated chitosan, the films obtained by drying hydrogel have a lower degree of crystallinity and a higher sorption capacity towards water vapor and Cu2+ ions, as well as the ability to retain up to 5000% of water during re-swelling without destruction.

Temperature-induced adsorption and desorption of phosphate on poly(acrylic acid-co-N-[3-(dimethylamino)propyl]acrylamide) hydrogels in aqueous solutions

Temperature-induced adsorption and desorption of phosphate on poly(acrylic acid-co-N-[3-(dimethylamino)propyl]acrylamide) hydrogels in aqueous solutions

Preparation and characterization of high-performance polyamic acid salt hydrogel in aqueous solution

Herein, we report an easy-to-prepare polyamic acid salt (PAAS) hydrogel with multiple functionalities including rapid self-healing, stimuli-responsive properties, and conductivity. This study describes a method for synthesizing PAAS hydrogel in aqueous solution. Phenylenediamine and 3,3′,4,4′-biphenyltetracarboxylic dianhydride were used to prepare a hydrogel with a fully aromatic backbone via gradual polymerization. It is possible to use the gel in the field of biomaterials in the absence of organic solvents. The prepared hydrogel was characterized using Fourier-transform infrared spectroscopy and dynamic rheometry. The gel has good toughness and the storage modulus and tensile stress are, respectively, about 0.25 and 0.45 MPa. Our study may pave the way for the manufacture of PAAS hydrogel, which may promote the development of hydrogel materials.

Supramolecular gel electrophoresis

Amphiphilic C3-symmetric tris-ureas self-assemble into supramolecular hydrogels in aqueous solution. These supramolecular hydrogels were used as matrices for the electrophoresis of biopolymers such as proteins and nucleic acids. A unique separation mode in comparison to that of typical sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE) was found during the electrophoresis of denatured proteins. Native proteins were separated on the basis of their isoelectric points and retained their activities. Affinity electrophoresis was realized by exploiting interactions between gelator glucosides and carbohydrate-binding proteins. Protein samples were efficiently recovered through an extremely simple operation, and up to 50% of the protein was extracted by centrifugation, which is a remarkable feature of electrophoresis using supramolecular hydrogels. Large DNA fragments that previously had been separated only by pulsed-field gel electrophoresis were separated using a supramolecular hydrogel matrix and a typical continuous-field electrophoresis apparatus. In this focus review, the author summarizes the electrophoresis of proteins and nucleic acids using our developed supramolecular hydrogel matrix. Amphiphilic C3-symmetric tris-ureas self-assemble into supramolecular hydrogels in aqueous solution. These supramolecular hydrogels were used as matrices for the electrophoresis of biopolymers (SUGE: SupramolecularGelElectrophoresis). A unique separation mode in comparison to that of SDS–PAGE was found during the electrophoresis of denatured proteins. Native proteins were separated on the basis of their isoelectric points and retained their activities. Large DNA fragments that previously had been separated only by pulsed-field gel electrophoresis were separated using a supramolecular hydrogel matrix and a typical continuous-field electrophoresis apparatus.

Adsorption and photocatalytic degradation of sulfamethoxazole by a novel composite hydrogel with visible light irradiation

A novel hydrogel catalyst (p(HEA/NMMA)-CuS) with the function of adsorption and degradation of organic pollutants in water was successfully synthesized using irradiation polymerization and in situ precipitation methods The composite hydrogel catalyst was characterized by SEM-EDS, TEM, swelling kinetics, zeta potential, TGA, XPS, FTIR and XRD. Besides, the effects and mechanisms of adsorption and degradation of sulfamethoxazole(SMX) as the representative pollutant by p(HEA/NMMA)-CuS hydrogel were observed. The results presented that adsorption process of SMX on complex hydrogel fit well to Langmuir monolayer adsorption, and followed a pseudo-second-order rate equation. The decomposition of SMX by p(HEA/NMMA)-CuS hydrogel in aqueous solution under 500w visible light achieved balance in 24h, the removal ratio reached 95.91%, and the SMX was mineralized with 43.56%. Hydroxyl radicals was detected as the reactive species using EPR in the system, degradation intermediates of SMX were further analyzed by LC-TOF-MSMS, a possible pathway for SMX degradation was presented. The degradation mechanism of SMX was also illustrated by theoretical calculations of frontier electron densities. Furthermore, mineralization, stability and regeneration results indicated that the developed hydrogel catalyst, p(HEA/NMMA)-CuS hydrogel, was promising in practical application.

Adsorption of phenazine dyes using poly(hydroxamic acid) hydrogels from aqueous solutions

Swelling and adsorption properties of poly(hydroxamic acid), (PHA) hydrogels in aqueous solutions of some phenazine dyes such as Neutral Red, Safranin T, and Janus Green have been investigated. PHA hydrogels containing N,N′ methylenebisacrylamide or ethyleneglycoldimethacrylate were used in experiments on swelling, diffusion and adsorption of the dyes. The equilibrium swelling (Seq) values of PHA hydrogels in aqueous solutions of the phenazine dyes were calculated as 2.16–33.25 g g−1. Swelling kinetic parameters such as initial swelling rate, swelling rate constant, and maximum swelling were found. Dye diffusion into hydrogels was found to be non‐Fickian in character. Diffusion coefficients are ranged 1.32 × 10−6 cm2 s−1 − 44.70 × 10−6 cm2 s−1. Adsorption of the phenazine dyes onto PHA hydrogels was studied by batch technique. PHA hydrogels in the phenazine dye solutions showed the dark coloration. The data was found that Freundlich isotherm model fits. According the Freundlich constants, the adsorption isotherms are of S‐type in Giles classification. All swelling and binding parameters for PHA‐EGDMA were found to be higher than those for PHA‐NNMBA. The type of crosslinker influenced the swelling, binding, and sorption more than the type of dye. Finally, it can be said that PHA hydrogels may be used a sorbent for removal of dyes. POLYM. ENG. SCI., 58:310–318, 2018. © 2017 Society of Plastics Engineers