Amphoteric Hydrogels Research Articles

Construction of amphoteric hydrogel electrolytes with charge modification: An investigation of ion migration mechanism and antibacterial property

Some challenges still hinder the advancement of hydrogel electrolytes, such as low ionic conductivity and restricted flexibility, which obstacle the effective integration of supercapacitors for flexible wearable devices. We developed an amphoteric hydrogel electrolyte with a highly ionic conductivity of 46.64 mS·cm−1, 927.32% of tensile strain and compressive strain to 85% in ambient air. Through lignin sulfomethylation and chitosan quaternization, abundant charge groups were introduced to the structure of hydrogel electrolyte to achieve charge modification. These charged groups not only promoted the dissociation of KOH, but also formed ion transport channels to enhance the migration of K+ and OH–. Note that the hydrogel also had significant antibacterial activity, enhancing its practical applicability. Moreover, the flexible supercapacitor constructed with this hydrogel electrolyte showed excellent capacitive performance, achieving a notable specific capacitance of 192.6 F·g−1 and a high energy density of 45.2 Wh·kg−1 under a current density of 0.5 A·g−1. In addition, the flexible supercapacitor also demonstrated remarkable rate performance and cycle stability, which maintained nearly constant coulombic efficiency (99.7%) and retaining 86.1% of capacitance retention after 10,000 charge–discharge cycles. Moreover, the flexible supercapacitor maintained stability under bend and load conditions, showing good deformation adaptability.

High-strength amphoteric hydrogel that can realize self-repairing of cement microcracks triggered by CO2 gas

During the completion of a natural gas well, the annular gas migration of the cement paste significantly damages the cement quality. Thus, the cement with self-repairing property has great significance in oil well applications. In this work, chemically cross-linked hydrogels were synthesized by the solution polymerization of acrylamide, acrylic acid, and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with NMBA as cross linker to plug the CO2-triggered microcracks in the cement paste. The mechanical strength of the hydrogel (Cu-PMAD) was significantly enhanced by complexation between Cu2+ and the carboxyl group of the hydrogel network. As a self-healing plugging material, Cu-PMAD hydrogel powder was mixed with cement to prepare self-repairing cement slurry. The amphoteric structure of hydrogel was triggered by CO2 due to the DMAEMA unit of the hydrogel was protonated, and the hydrogel can swell further by the anti-polyelectrolyte effect under CO2 of nature gas and formation salt-bearing fluid. The good swelling ability and mechanical properties endowed the Cu-PMAD hydrogel with excellent plugging ability for cement microcracks triggered by CO2.

Synthesis and characterization of methacrylic acid based amphoteric hydrogels: use as a dual drug delivery system

In this study, methacrylic acid-based containing both anionic and cationic groups in its structure p(Methacrylic acid-co-(3-acrylamidopropyl)trimethylammonium chloride) (p(MAA-co-APTMACl)) and p(Methacrylic acid-co-(2-(acryloyloxy)ethyl)trimethylammonium chloride) (p(MAA-AETAC)) hydrogels were synthesized by redox polymerization technique. The morphology, chemical structure and thermal properties of the synthesized hydrogels were characterized by SEM, FT-IR, and TGA. The swelling characterizations of the synthesized MAA-based hydrogels were carried out in various biological environments. Usability of amphoteric hydrogels containing anionic and cationic groups in their structures as a drug carrier cargo material were investigated for the treatment of two different diseases. For this, two of the selected model drugs were loaded simultaneously on hydrogels and their release properties were examined. The drug release mechanisms were investigated according to the Korsmeyer–Peppas model. Rhodamin 6G and ceftriaxone sodium were loaded to p(MAA-co-APTMACl) hydrogel for dual drug release. In addition, Rhodamin 6G and sulfadiazine were loaded simultaneously on the p(MAA-co-AETAC) hydrogel. According to the release mechanism results obtained for p(MAA-co-AETAC) hydrogels, it was determined that it showed a super-state diffusion mechanism. In addition, antibacterial activities of p(MAA-co-APTMACl) and p(MAA-co-AETAC) hydrogels against gram-negative bacteria (Escherichia coli and Pseudomonas Aeruginosa) and gram-positive bacteria (Staphylococcus Aureus and Bacillus Subtilis) were investigated.

Molecular imprinting of bovine serum albumin and lysozyme within the matrix of polyampholyte hydrogels based on acrylamide, sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid and (3-acrylamidopropyl)trimethyl ammonium chloride

Molecularly-imprinted polyampholyte (MIP) hydrogels based on nonionic monomer – acrylamide (AAm), anionic monomer – sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and cationic monomer – (3-acrylamidopropyl)trimethyl ammonium chloride (APTAC) were obtained by immobilization of bovine serum albumin (BSA) and lysozyme in situ polymerization conditions. It was found that the best amphoteric hydrogel for sorption of BSA is APTAC-75H while for sorption of lysozyme is AMPS-75H. The sorption capacity of APTAC-75H and AMPS-75H with respect to BSA and lysozyme is 305.7 and 64.1-74.8 mg per 1 g of hydrogel respectively. Desorption of BSA and lysozyme from MIP template performed by aqueous solution of 1M NaCl is equal to 82-88%. Separation of BSA and lysozyme from their mixture was performed on MIP templates. The results of adsorption-desorption cycles of BSA on adjusted to BSA polyampholyte hydrogel APTAC-75H and of lysozyme on adjusted to lysozyme polyampholyte hydrogel AMPS-75H show that the mixture of BSA and lysozyme can be selectively separated with the help of MIP hydrogels.

Synthesis, characterization and swelling behavior of high-performance antimicrobial amphoteric hydrogels from corn starch

Three novel hydrogels with high antimicrobial activity were synthesized from grafting of corn starch with 4-acrylamidobenzoic acid (4ABA) and diallyldimethylammonium chloride as cross-linkers (CLs). Three concentrations of the cross-linker (3%, 5% and 10% based on starch weight) were used to give three hydrogels designated as St-g-P4ABA/PCL3, St-g-P4ABA/PCL5 and St-g-P4ABA PCL10, respectively. The structure of the prepared hydrogels was evidenced by FTIR, 1H-NMR, XRD and SEM techniques. The thermal stability as well as the swelling behavior of the starch hydrogels was investigated, and the results revealed high thermal stability and potential swell ability in water and 9% saline solution for the hydrogels compared with the native starch. They showed a higher swelling degree in acidic, basic and neutral buffer solutions; lower degradation was observed in acidic and basic media after 96 h. Starch hydrogel's antimicrobial activity actions against various types of gram-positive bacteria, gram-negative bacteria and fungi demonstrated higher growth inhibition ability against all tested microorganisms compared to zero-native starch inhibitions. The hydrogels did not demonstrate cytotoxicity on normal human cells and can therefore be used safely in pharmaceutical applications and drug delivery systems.

Double network hydrophobic starch based amphoteric hydrogel as an effective adsorbent for both cationic and anionic dyes

A double-network hydrophobic-hydrogel was successfully synthesized. Here epichlorohydrin (ECH) and N, N-methylene bis-acrylamide act as the crosslinkers for starch and poly(acrylic acid), respectively. The synthesized hydrogel having both positive and negative charge exhibited amphoteric properties and employed for the exclusion of anionic and cationic dyes from waste aqueous solution. The formation of positive charge occurs via reaction of triethylamine with the open up epoxy ring of ECH while carboxylate ion of poly(acrylic acid) gives the negative charge in the hydrogel. The formation of double cross-linking and the presence of quaternized alkyl chains lead towards hydrophobicity with much lower swelling ability. As an adsorbent, the hydrogel was able to remove both cationic dye (methylene blue) and anionic dye (congo red) with adsorption maxima of 133.65 mg/g and 64.73 mg/g, respectively. This study showed that the synthesized hydrogel offers enormous potential as the toxic dye adsorbent for effluent treatment of industrial wastewater.

Intra- and Interpolyelectrolyte Complexes of Polyampholytes.

At present, a large amount of research from experimental and theoretical points of view has been done on interpolyelectrolyte complexes formed by electrostatic attractive forces and/or interpolymer complexes stabilized by hydrogen bonds. By contrast, relatively less attention has been given to polymer–polymer complex formation with synthetic polyampholytes (PA). In this review the complexation of polyampholytes with polyelectrolytes (PE) is considered from theoretical and application points of view. Formation of intra- and interpolyelectrolyte complexes of random, regular, block, dendritic polyampholytes are outlined. A separate subsection is devoted to amphoteric behavior of interpolyelectrolyte complexes. The realization of the so-called “isoelectric effect” for interpolyelectrolyte complexes of water-soluble polyampholytes, amphoteric hydrogels and cryogels with respect to surfactants, dye molecules, polyelectrolytes and proteins is demonstrated.

Finite Element Simulation and the Application of Amphoteric pH-sensitive Hydrogel

Amphoteric hydrogels have been widely used in biologic and mechanic areas such as robot joints, biological cells, drug delivery systems. There are many factors that can influence the deformation of hydrogels, such as pH value, concentration of salt ions, solid constrains and external force, which all together makes the calculation very complicated. In this paper, an improved model for the calculation of amphoteric pH-sensitive hydrogels’ deformation is developed so that the behaviors of hydrogels in both acidic and alkaline solutions can be described quantitatively, and this model is implemented into finite element method (FEM) software ABAQUS in order to simulate hydrogel’s homogeneous and inhomogeneous deformations. The FEM results under free swelling state are compared with both analytical solution and FEM results existed before, and FEM results fit well with the experimental data. The buckling of amphoteric pH-sensitive hydrogel membrane is also analyzed, some natural phenomena, such as the wrinkling of human finger’s skin and the broad bean testa are successfully explained.

Preparation of amphoteric nanocomposite hydrogel under supercritical carbon dioxide and its fast-swelling behaviours

Supercritical carbon dioxide (scCO2) has been widely used in preparation of nanocomposite materials. However, so far there has been no report on preparation of nanocomposite hydrogels by intercalation of hydrophilic monomers into clay under scCO2 condition. In this paper, the fast-swelling amphoteric nanocomposite hydrogels were prepared via the free radical polymerisation of acrylic acid (AA) and N-[3-(dimethylamino) propyl] methacrylamide (DMAPMA) in the presence of clay under scCO2 condition. The composition of the hydrogel was determined by element analysis and Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) results illustrated that the clay layers became disordered after intercalation by AA and DMAPMA under scCO2 condition. The swelling kinetics and deswelling characteristics were tested. The results indicated that the hydrogels presented marked swelling rate in deionised or saline water and fast deswelling rate in alcoholic solution.

An amphoteric hydrogel: Synthesis and application as an internal curing agent of concrete

ABSTRACTA new crosslinked amphoteric hydrogel (PAC) was synthesized and evaluated as an internal curing agent of concrete. PAC was prepared from acrylamide (AM) and 4‐(2‐((carboxylatomethyl)dimethylammonio)ethoxy)−4‐oxobut‐2‐enoate (CMD) through free‐radical polymerization by using ammonium persulfate (APS) as an initiator and methylene‐bisacrylamide (MBA) as a crosslinker. The structure of the prepared polymer was verified by the IR spectra. The effects of the polymerization variables on the swelling capacity of PAC were investigated. The water absorbency of PAC was found to increase with increasing CMD/AM ratio, reach a maximum value, and decrease afterword. Increase of either APS or MBA content decreased the water absorbency. The highest water absorbency of PAC hydrogel (P7) achieved in deionized water, 0.1M NaCl solutions and 0.1M CaCl2 solutions, was 306 g/g, 32 g/g, and 22 g/g, respectively. Compared with a commercial acrylate‐based hydrogel 283HA, P7 was less sensitive to the existence of Ca2+ ions in cement pore solutions, and more effective in reducing the cracking tendency of cement pastes. Finally, mortars incorporated with proper amounts of P7 showed smaller drying shrinkage and higher compressive strength than that without hydrogel present. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42175.

Adsorption behaviors of ammonium nitrogen by an amphoteric hydrogel

An amphoteric hydrogel was prepared by cross-linking graft copolymerization of dimethyldiallylammonium chloride and acrylic acid onto soluble starch. The adsorption behaviors of ammonium nitrogen (NH4+-N) by the amphoteric hydrogel were discussed in this study. The effects of various experimental parameters on NH4+-N removal, including pH, the dose of absorbent, the temperature, the adsorption time, and the initial concentration of NH4+-N, were investigated. The result indicated that the amphoteric hydrogel showed a fast adsorption rate and high adsorption capacity for NH4+-N in a pH range from 4 to 8. The adsorption process was exothermic according to the value of thermodynamic parameters. The adsorption process fits the pseudo-second-order kinetic model best. To this hydrogel, it was seen that the Freundlich adsorption isotherm model fits the adsorption data better. The adsorption capacity could reach to 33.98 mg/g. The hydrogel showed the potential use for removal of NH4+-N in water treatment and fishing industry.

Influence of environmental solution pH and microstructural parameters on mechanical behavior of amphoteric pH-sensitive hydrogels

Amphoteric hydrogels contain both ionizable acidic and basic groups attached on the polymer chains, which can change their volume in response to the slight alteration of the surrounding environmental p H. In this paper, a theory of equilibrium swelling of amphoteric p H-sensitive hydrogels which is an extension of the formalism proposed by Marcombe et al. and a new hybrid free-energy density function of amphoteric hydrogels composed of the Edwards-Vilgis slip-link model and the Flory-Huggins solution theory as well as the contributions of mixing the mobile ions with the solvent, and dissociating the acidic and basic groups are presented for the prediction of the influence of environmental solution p H, microstructural parameters and geometric constraints on mechanical behavior. The calculations were modeled on chitosan-genipin gels, and the results were compared to experimental data. Numerical calculations show that the model is able to predict the dependence of swelling on p H and crosslinker qualitatively well and quantitatively close to the experimental data. Each gel shows minimal swelling at low p H but an increase in swelling until a maximum was reached; for most of the p H range, a good fit was achieved except for where the maximum swelling occurs; for experimental data, the maximum swelling appears at about pH = 4 , but for modeled data the maximum swelling appears between pH = 4 and pH = 6 ; each gel swell decreasing with increasing crosslinker concentration was also successfully predicted. The calculated results also show that microstructural parameters and geometric constraints have a significant impact on the mechanical behavior of the amphoteric hydrogels; the gel swells less when the network is more densely entangled and the maximum swelling ratio of the gels under biaxial constraint is only about one-third of the maximum when the gels swell freely. The theory developed here is valuable for the design and optimization of a drug delivery system.

Preparation and swelling behavior of pH-sensitive and saltresistant amphoteric semi-IPNs hydrogels based on starch phosphate and poly[2-[(methacryloyloxy) ethyl] trimethylammonium] chloride

AbstractA novel amphoteric hydrogel with semi-interpenetrating polymer networks (semi-IPNs), was prepared by entrapping linear poly[2-[(methacryloyloxy) ethyl]trimethylammonium] chloride (PDMC) into lightly crosslinked starch phosphate- graft-acrylic acid (St-OPO3-g-AA) network in aqueous solution. The influences including the degree of substitution (DS) of starch phosphate, the doses of crosslinker, AA and PDMC were investigated with respect to the swelling capacity. The swelling capacity of hydrogel reached 2016 g/g in deionized water and 121 g/g in 0.9 wt% NaCl solutions, respectively. The swelling behaviors of hydrogel in various salt solutions and different pH buffer solutions were discussed. The amphoteric semi-IPN hydrogels exhibited pH-sensitivity and salt-resistance.

Compression elastic modulus of neutral, ionic, and amphoteric hydrogels based on N‐vinylimidazole

AbstractSeveral hydrogels of N‐vinylimidazole and sodium styrenesulfonate have been prepared by radical cross‐linking copolymerization in aqueous solution, using N,N′‐methylene‐bisacrylamide as crosslinker. Depending on composition, these hydrogels were neutral, amphoteric, cationic or anionic. Compression‐strain measurements were performed on samples as‐synthesized and swollen in deionized water or in acid aqueous solutions, with and without salt. It was thus found that the cross‐linking densities determined by compression measurements on as‐synthesized samples are in good accordance with those calculated by means of the model of polymer networks with pendant vinyl groups. A non‐Gaussian parameter (β) was introduced to explain that the elastic moduli (G) of samples swollen at equilibrium are larger than predicted by the Gaussian model. The β values of the neutral or ionized systems increase with swelling and fall into a single curve, which denotes a common behavior. Swelling has two opposite effects on G; on the one hand G decreases because the polymer volume fraction diminish and the system shifts from the affine limit to the phantom one; on the other, β increases and contributes to increasing G. The balance of those two opposite effects determines the variation of G with swelling. The possible contribution of ionic crosslinks to νe for the polyampholyte and for the polycation wearing divalent counteranions was discussed. A peculiar system is poly(sodium styrenesulfonate), whose cross‐linking density is much lower than expected. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1078–1087, 2009

SYNTHESIS AND CHARACTERIZATION OF AMPHOTERIC HYDROGELS BASED ON N-CARBOXYETHYLCHITOSAN

New amphoteric hydrogels based on carboxyethylchitosans (CECH) with various degrees of substitution (DS) were prepared using different amounts of epichlorohydrin (ECH) as the crosslinking agent. The equilibrium swelling ratio (SW) was determined as functions of pH and salt concentration. The hydrogels show typical amphoteric character responding to pH change of the external medium. At isoelectric point (IEP), the hydrogels shrink. The DS value has important effect on the swelling properties of the hydrogels. When the DS of N-carboxyethylchitosan increases from 0.32 to 0.72, the equilibrium swelling ratio (SW) of the hydrogel changes from 76 to 290 at pH 7.3 and from 117 to 499 at pH 11.3. A marked volume decrease was observed in hydrogels with increasing salt concentration in the surrounding solution. The viscoelastic properties of the hydrogels were studied by oscillatory shear measurements under small-deformation conditions. The elastic modulus G' of all the samples has no dependence on frequency and is one order of magnitude larger than the loss modulus G", corresponding to a strong gel behavior.

Electrical Behavior of a Natural Polyelectrolyte Hydrogel: Chitosan/Carboxymethylcellulose Hydrogel

An amphoteric hydrogel film was prepared by solution blending of two natural polyelectrolytes, chitosan and carboxymethylcellulose, and cross-linking with glutaraldehyde. The bending of the film in an electric field was studied in different electrolyte solutions. Because of its amphoteric nature, the hydrogel can bend toward either anode or cathode depending on the pH of the solution. Other factors such as ionic strength and electric field strength also influence the electromechanical behavior of the hydrogels. The equilibrium bending angle of the hydrogel was found to reach a maximum at about 90 degrees in pH = 6 Britton-Robinson buffer solution with an ionic strength of 0.2 M. The sensitivity of the films over a wide range of pH and the good reversibility of this natural amphoteric electric-sensitive hydrogel suggest its future use in microsensor and actuator applications, especially in the biomedical field.

Amphoteric hydrogels for immobilization of enzymes using template polymerization technique

AbstractNovel ionizable amphoteric hydrogels were prepared from poly(acrylic acid) and dimethylaminoethyl methacrylate monomer, employing template polymerization technique. The mode of interaction, as proved by FTIR, was multiple H‐bonding between the tertiary amino group of the monomer and the carboxylic groups of the polymer. The impact of varying equal polymer–monomer feed ratios from 0.1 to 1.1 on the swelling dynamics was examined. Penetrant sorption experiments demonstrated that the swelling behavior depends strongly on the polymer complex composition. The polymer complex of feed ratio 0.5 : 0.5 (polymer : monomer) showed maximum swelling percentage. The mechanism of the polymer complexes swelling was probably a non‐Fickian with n values approaching Fickian behavior. The hydrogels showed maximum swelling efficiencies of 27 folds and 13.5 folds in drastic acidic and basic medium, respectively, using polymer complex of 0.5 : 0.5 feed ratio. Because of reversibility and rapidity of swelling, the gel could be considered as a mechanochemical system. The prepared hydrogel successfully immobilized the industrially used β‐galactosidase as an acidic model enzyme. The novel immobilized enzyme showed a remarkable improvement in its activity (13.8 μmol min−1 mg−1) compared to the free enzyme (3.2 μmol min−1 mg−1). The optimum pH values for free and immobilized enzyme were 4.5–5 and 4, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

A new amphoteric superabsorbent hydrogel based on sodium starch sulfate

A new amphoteric superabsorbent hydrogels were synthesized by graft copolymerization blending based on acrylamide (AM), diallydimethylammonium chloride (DMDAAC) and sodium starch sulfate (SSS). The effect of polymerization conditions on swelling capacity was investigated. The results showed that the swelling capacity was affected by various factors, such as polymerization temperature, concentration of initiator and crosslinker, and dose of AM. Additionally, the results testified that salt bond was a potential crosslinking factor in the amphoteric hydrogel. The maximum swelling capacity in distilled water and saline solution reached 1493.1 and 91.0 g/g, respectively. These results were compared with those obtained from original starch-based hydrogel.

Preparation and release profiles of pH/temperature-responsive carboxymethyl chitosan/P(2-(dimethylamino) ethyl methacrylate) semi-IPN amphoteric hydrogel

Thermo- and pH-responsive semi-IPN polyampholyte hydrogels were prepared by using carboxymethyl chitosan and P(2-(dimethylamino) ethyl methacrylate) with NN'-Methylenebisacrylamide (BIS) as crosslinking agent. It was found that the semi-IPN hydrogel shrunk most at the isoelectric point (IEP) and swelled when pH deviated from the IEP. Its swelling ratio dramatically decreased between 30 and 50 °C at pH 6.8 buffer solution. It also showed good reversibility. The UV results showed that when the pH values of drug release medium were 3.7, 6.8, and 9 at 25 °C, the cumulative release rates reached 83.1, 51.5, and 72.2%, respectively. The release rate of coenzyme A (CoA) was higher at 50 °C than 37 and 25 °C at pH 6.8 solution. The release rate decreased with increasing the content of carboxymethyl chitosan at 25 °C in pH 6.8 solution. The results showed that semi-IPN hydrogel seems to be of great promise in pH/temperature drug delivery systems.

Amphoteric Hydrogel Capsules: Multiple Encapsulation and Release Routes

We show that chemical cross-linking of hydrogen-bonded poly(methacrylic acid)/poly(vinylpyrrolidone) (PMAA/PVPON) capsules deposited onto silica core with ethylenediamine (EDA) followed by core dissolution and pH-triggered removal of PVPON produces amphoteric hydrogel hollow capsules, whose walls are composed of cross-linked PMAA and contain amino groups provided by the cross-linker. The capsules exhibit highly reversible swelling at acidic and basic pH values due to excess positive and negative charges in the capsule wall and are of minimum size at pH 5.5. Apart from covalent cross-linking, the hydrogel capsule wall is also stitched through ionic pairing in a wide interval of pH. At pH 5−6, where carboxylic acid groups are protonated, the capsule wall expands (and hydrogel capsules increase in size) in salt solutions as a result of dissociation of ionic cross-links. In contrast, at pH > 6 and pH < 5, where hydrogel wall acquires charge, salt results in the hydrogel contraction and in a decrease of capsule size. In addition to pH and ionic strength, capsule swelling can be controlled by the number of cross-links achieved through variation of cross-linking time. We also show that these soft hydrogel capsules easily flatten when in contact with a solid surface and that the degree of flattening is governed by the surface and capsule charge and the degree of cross-linking in the capsule wall. Finally, we demonstrate that this pH- and ionic-strength-dependent swelling of hydrogel capsules affords multiple routes for encapsulation and controlled release of macromolecules.