Cationic Hydrogels Research Articles

Adsorption of Sodium Cholate on Cationic Dextran Gels: Comparison of Isotherm Binding Models

Cationic dextran hydrogels having pendent 51-59 mol% N-alkyl-N,N-dimethylammonium chloride groups were synthesized and tested as adsorbents for sodium cholate. The bile acid salt sorption by these gels was evaluated by equilibrium analysis in water and 10 mM NaCl solution. The best adsorption results were obtained with amphiphilic dextran-based gels having two types of pendant ammonium chloride groups with different polarities. Experimental adsorption data for all polymers fitted good with Langmuir, Dubinin-Raduskevich and Temkin models over the entire range of ligand concentrations. The maximum experimental adsorption capacity of dextran sorbents for sodium cholate was in the range 850-1075 mg/g.

Simultaneous Adsorption of Cation and Anion by Thermosensitive Hydrogels

Simultaneous usage of cationic and anionic thermosensitive hydrogels was shown to positively contribute to adsorption of heavy metal ions. The potential capacity for recovering heavy metal ions from an aqueous solution was enhanced by incorporating relatively hydrophobic moiety to the hydrogels, which was ascribed to the increase in the desorption on elevating the temperature over the lower critical swelling temperature (LCST). N-tert-butylacrilamide was added into the hydrogels to increase its desorption potential. The addition of N-tert-butylacrylamide does not significantly affect hydrogels’ adsorption ability. Moreover, the adsorption-desorption cycle was not diminished by repeating the temperature swing above the critical temperature at which the volume phase transition was induced.

Cationic Self-Assembled Peptide-Based Molecular Hydrogels for Extended Ocular Drug Delivery

Cationic Self-Assembled Peptide-Based Molecular Hydrogels for Extended Ocular Drug Delivery

Cationic Cross-Linked Nanocellulose-Based Matrices for the Growth and Recovery of Intestinal Organoids.

Highly carboxylated nanocellulose fibers can be functionalized with cell adhesive peptides and cationic cross-linked to form matrices for a three-dimensional (3D) cell culture. It is hypothesized that nanocellulose hydrogels cross-linked with divalent cations can provide the required biochemical and mechanical properties for intestinal organoid growth and recovery. Nanocellulose hydrogels are produced by TEMPO- and TEMPO-periodate-mediated oxidation and functionalized with RGD peptides. Mechanical properties are measured by rheology and optical properties quantified by UV-vis spectroscopy. Cellulosic matrices are cross-linked with Ca2+ and Mg2+ and intestinal organoids cultured for 4 days. The organoids are recovered for passaging and RNA extraction. TEMPO-periodate-oxidized nanocellulose fibers form functionalized hydrogels and support the growth of intestinal organoids. The highly transparent cellulosic matrix requires 4 times more Mg2+ than Ca2+ ions to reach the targeted stiffness. Organoids cultured in nanocellulose maintained a major living area for up to 4 days. Cell clusters recovered from magnesium-cross-linked hydrogels can be passaged, and their extracted RNA is intact. Cationic cross-linked nanocellulose hydrogels are promising alternative plant-based matrices for a 3D cell culture systems.

Removal of anionic dyes from aqueous media by using a novel high positively charged hydrogel with high capacity

Poly((methacryloylamino)propyl trimethylammonium chloride-co-vinylimidazole) (p(MAPTAC-co-VI)) hydrogels were synthesized through free radical polymerization of 3-(methacryloylamino)propyl trimethylammonium chloride (MAPTAC) and 1-vinylimidazole (VI) in aqueous solutions with ammonium persulfate (APS) used as initiator and N,N′-methylenebis(acrylamide) (MBA) as the crosslinking agent. By modifying with HCl, the positive charge density on the hydrogel network structure was increased and quaternized hydrogels (p(MAPTAC-co-VI)-q) were obtained. Traditional swelling and spectrophotometric characterization techniques were used to gain a better understanding of the performance of cationic hydrogels for the removal of anionic dyes. FTIR, SEM, and EDX confirmed the structure of the hydrogel before and after the adsorption process. Later, dye adsorption performance of these p(MAPTAC-co-VI)-q hydrogels was investigated under different adsorption conditions, including initial concentration, temperature, pH values of dye solutions, and adsorption contact time, adsorbent dosage and in real water samples. Various isotherm and kinetic models of dye adsorption by the hydrogel were also studied and the experimental adsorption followed a pseudo-second order model and fitted the Langmuir isotherm well. Thanks to the effective use of existing adsorption sites, high adsorption capacity was achieved for eriochrome black T (EBT) and methyl orange (MO) dyes. The values of qmax are as follows: 1818.2 mg/g and 1449.3 mg/g, respectively. Thermodynamic parameters indicate that the process was spontaneous and endothermic. P(MAPTAC-co-VI)-q hydrogels can be used as a potential adsorbent for removal of anionic dye molecules, one of the industrial pollutants, from wastewater.

Microwave radiation-assisted covalent functionalization of boron nitride nanotubes and their grafting with cationic thermo and pH-sensitive hydrogel

Sensitive hydrogels target the delivery of chemotherapeutic drugs to tumor tissues as these polymeric nets respond to environmental changes caused by growing cancerous tissues. A major concern with hydrogels is low mechanical resistance, what could be mitigated by combining these polymers to mechanically resistant inorganic materials like nanotubes. Boron nitride nanotubes (BNNT) exhibit biocompatibility and high mechanical resistance but are unable to control the release of molecules based on the conditions of a given suspension medium. Grafting sensitive hydrogels to BNNT presents a way to gather features of both phases, creating a potential drug delivery system (DDS) capable of withstanding the shear stress of the bloodstream. In this study BNNT were obtained via chemical vapor deposition (CVD) and oxidized by strong acids before being covalently functionalized by microwave radiation-assisted grafting. Thermo and pH-sensitive Poly[(N-iPAAm)-co-(DEAEMA)] hydrogels were synthesized using free radical polymerization both isolated, creating a purely polymeric sample, and in the presence of functionalized BNNT, creating the BNNT-TEGDMA/Poly[(N-iPAAm)-co-(DEAEMA)] hybrid sample. The hybrid sample represents the first time that, to the best of our concern, BNNT have been coated with in situ synthesized cationic hydrogel. The samples were characterized using XRD, SEM, TEM–EELS, FTIR, XPS, TGA, DSC, and elemental analysis. The results indicate that BNNT were successfully synthesized, oxidized, and covalently functionalized. These results also show that hydrogels were obtained in the absence and in the presence of functionalized nanotubes and could form the dual-phase hybrid material, which was shown to be sensitive to temperature and pH variations.

Water-Borne Isocyanate-Free Polyurethane Hydrogels with Adaptable Functionality and Behavior.

Polyurethane hydrogels are attractive materials finding multiple applications in various sectors of prime importance; however, they are still prepared by the toxic isocyanate chemistry. Herein the facile and direct preparation in water at room temperature of a large palette of anionic, cationic, or neutral polyurethane hydrogels by a non-isocyanate route from readily available diamines and new hydrosoluble polymers bearing cyclic carbonates is reported. The latter are synthesized by free radical polymerization of glycerin carbonated methacrylate with water-soluble comonomers. The hydrogel formation is studied at different pH and its influence on the gel time and storage modulus is investigated. Reinforced hydrogels are also constructed by adding CaCl2 to the formulation that in-situ generates CaCO3 particles. Thermoresponsive hydrogels are also prepared from new thermoresponsive cyclic carbonate bearing polymers. This work demonstrates that a multitude of non-isocyanate polyurethane hydrogels are easily accessible under mild conditions without any catalyst, opening new perspectives in the field.

Donnan Contribution and Specific Ion Effects in Swelling of Cationic Hydrogels are Additive: Combined High-Resolution Experiments and Finite Element Modeling.

Finite element modeling applied to analyze experimentally determined hydrogel swelling data provides quantitative description of the hydrogel in the aqueous solutions with well-defined ionic content and environmental parameters. In the present study, we expand this strategy to analysis of swelling of hydrogels over an extended concentration of salt where the Donnan contribution and specific ion effects are dominating at different regimes. Dynamics and equilibrium swelling were determined for acrylamide and cationic acrylamide-based hydrogels by high-resolution interferometry technique for step-wise increase in NaCl and NaBr concentration up to 2 M. Although increased hydrogel swelling volume with increasing salt concentration was the dominant trend for the uncharged hydrogel, the weakly charged cationic hydrogel was observed to shrink for increasing salt concentration up to 0.1 M, followed by swelling at higher salt concentrations. The initial shrinking is due to the ionic equilibration accounted for by a Donnan term. Comparison of the swelling responses at high NaCl and NaBr concentrations between the uncharged and the cationic hydrogel showed similar specific ion effects. This indicates that the ion non-specific Donnan contribution and specific ion effects are additive in the case where they are occurring in well separated ranges of salt concentration. We develop a novel finite element model including both these mechanisms to account for the observed swelling in aqueous salt solution. In particular, a salt-specific, concentration-dependent Flory–Huggins parameter was introduced for the specific ion effects. This is the first report on finite element modeling of hydrogels including specific ionic effects and underpins improvement of the mechanistic insight of hydrogel swelling that can be used to predict its response to environmental change.

Removal of dye from aqueous medium with pH-sensitive poly[(2-(acryloyloxy)ethyl]trimethylammonium chloride-co-1-vinyl-2-pyrrolidone] cationic hydrogel

In this study, p([2-(acryloyloxy)ethyl]trimethylammonium chloride-co-1-vinyl-2-pyrrolidinone) (p(AETAC-co-NVP) hydrogels containing positive charge in the structure were synthesized for the removal of anionic dyes from the aqueous media. The swelling behaviors affecting the adsorption properties of hydrogels structurally characterized by FTIR, SEM and EDX/mapping analysis were investigated. The effects of pH, dye concentration, adsorbent amount, dissolved anions and temperature on the adsorption of methyl orange (MO) and alizarin red S (AR) from aqueous media using p(AETAC-co-NVP) hydrogels were investigated. Using data obtained in adsorption studies, the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms and pseudo-first order (PFO), pseudo-second order (PSO), intra-particular diffusion, and Elovich kinetic model analyses were performed. The results showed that the p(AETAC-co-NVP) hydrogel was a good adsorbent for MO and AR anionic dyes and the adsorption process for both dyes complied with the Freundlich isotherm and PSO kinetic model. This situation indicates that the dominant mechanism for the adsorption of MO and AR dyes by the p(AETAC-co-NVP) hydrogel is strong electrostatic interactions and occurs as multilayered adsorption, not only on a planar region. Additionally, to the maximum adsorption values using p(AETAC-co-NVP) hydrogel for MO and AR dyes were reached at pH values of 7.0 and 5.0, respectively. According to all these findings, it can be said that the p(AETAC-co-NVP) hydrogel containing positivelly charged groups is a super adsorbent for adsorption of anionic dyes.

Desalination of Seawater Using Cationic Poly(acrylamide) Hydrogels and Mechanical Forces for Separation

AbstractIn this study, the ability of cationic poly(acrylamide‐co‐(3‐acrylamidopropyl)trimethylammonium chloride) hydrogels to desalinate seawater is explored, where the salt separation is based on the partial rejection of mobile salt ions by the fixed charges along the polymer backbone. Water absorbency measurements reveal that artificial seawater‐containing divalent ions (Mg2+, Ca2+, and SO42−) drastically decrease the swelling capacity of previously employed anionic poly(acrylic acid‐co‐sodium acrylate) hydrogels, whereas no influence on the swelling behavior of the synthesized cationic hydrogels is found. The swelling behavior and mechanical properties are studied by varying the degree of crosslinking and degree of ionization systematically in the range of 1–5 and 25–75 mol%, respectively. Finally, artificial seawater (csea = 0.171 mol L−1) is desalinated in a custom‐built press setup with an estimated efficiency of Em³ = 17.6 kWh m−³ by applying an external pressure on the swollen hydrogels.

Bactericidal effect of cationic hydrogels prepared from hydrophilic polymers

AbstractThis study investigated whether hydrogels comprising hydrophilic cationic polymers have similar bactericidal effects. Bacteria were seeded on hydrogels and agar and their viability was assessed with time. Cationic hydrogels displayed bactericidal effects upon long‐term bacterial contact. Furthermore, we assessed the areal density of cationic monomer unit of the cationic hydrogels, water content, and the initial elastic modulus. We examined correlations between each factor and bacterial death ratios; consequently, the bacterial death ratios were strongly correlated with the areal density of cationic hydrogel monomers. Elastic energy (Wel) generated at the cytomembrane ion‐binding region and the cationic hydrogel and the cytomembrane interfacial energy (Wf) were estimated; consequently, Wel exceeded Wf at higher contact areas. The cationic hydrogel may extract cytomembranes with a reasonable adsorption area. Therefore, cationic hydrogels may be used as probes for ultrasonic echo to sterilize medical equipment.

Rational design of phosphonate/quaternary amine block polymer as an high-efficiency antibacterial coating for metallic substrates

Developing advanced technologies to address the bacterial associated infections is an urgent requirement for metallic implants and devices. Here, we report a novel phosphonate/quaternary amine block polymer as the high-efficiency antibacterial coating for metallic substrates. Three pDEMMP-b-pTMAEMA block polymers that bearing identical phosphonate segments (repeat units of 15) but varied cationic segments (repeat units of 8, 45, and 70) were precisely prepared. Stable cationic polymer coatings were constructed on TC4 substrates based on the strong covalent binding between phosphonate group and metallic substrate. Robust relationship between the segment chain length of the polymer coating and the antibacterial property endowed to the substrates have been established based on quantitative and qualitative evaluations. Results showed that the antibacterial rate of the modified TC4 surface were 95.8 % of S. aureus and 92.9 % of E. coli cells attached. Interestingly, unlike the cationic free polymer or cationic hydrogels, the surface anchored cationic polymers do compromise the viability of the attached C2C12 cells but without significant cytotoxicity. In addition, the phosphonate/quaternary amine block polymers can be easily constructed on titanium, stainless steel, and Ni/Cr alloy with significantly improved antibacterial property, indicating the generality of the block polymer for surface antibacterial modification of bio-metals.

Cationic hydrogels prepared from regioselectively azidated (1→3)-α-d-glucan via crosslinking and amination: Physical and adsorption properties

Cationic hydrogels with amino groups were successfully prepared using (1→3)-α-d-glucan synthesized by glucosyltransferase J (GtfJ) cloned from Streptococcus salivarius through a three-step reaction: (i) Azido groups were regioselectively introduced at the C6 position of (1→3)-α-d-glucan by a bromination-azidation process (degree of substitution 0.94), (ii) Azido groups were partially crosslinked with 1,8-nonadiyne via a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, (iii) Azido groups that were unused for crosslinking were reduced to amino groups by sodium borohydride (NaBH4). The introduction of amino groups was confirmed quantitatively and qualitatively by elemental, Fourier transform infrared (FT-IR), and nuclear magnetic resonance (NMR) analyses. These cationic hydrogels showed a specific adsorption ability for bovine serum albumin (BSA) over a wide pH range of 4.5–8.0 due to their high pH values at the point of zero charge (pHpzc 8.80–8.92).

Effect of mold assemblies-induced interfaces in the mechanical actuation of electro-responsive ionic liquid-based polycationic hydrogels

This work aims the development of electro-active polycationic soft-actuators based on copolymers of 2-hydroxyethyl methacrylate (HEMA) and 1-butyl-3-vinylimidazolium chloride (BVImCl), cross-linked with N,N’-methylene bis(acrylamide), and reinforced with mesoporous silica nanoparticles. Polycationic hydrogels were obtained by free radical polymerization in aqueous solution and using mold assemblies presenting different surface properties (e.g. Teflon® and glass). Obtained results demonstrated that a mold assembly-induced effect, at the mold/polymerization solution interface, originates “surface-to-bulk” heterogeneous copolymer concentration gradients when using Teflon®-Teflon® and Teflon®-glass mold assemblies, while homogeneous hydrogel networks were obtained when using only glass mold assemblies. Results were compared with those obtained from cross-linked poly(2-hydroxyethyl methacrylate) hydrogels to prove that the observed surface-induced polymerization effect occurs only in the presence of the ionic liquid co-monomer. Hydrogels synthesized in Teflon®-Teflon® molds presented the highest mechanical response under external electric stimulus and in different aqueous media of different pH and ionic strength. On the contrary, hydrogels synthesized in glass-glass mold assemblies presented limited mechanical actuation and only when immersed in saline aqueous media. The mechanical actuation of hydrogels synthesized in Teflon®-glass molds was shown to depend on the orientation of the applied electric current. The electro-actuation response of the synthesized electro-active polycationic hydrogels was discussed based on the ion enrichment/depletion mechanism. All prepared cationic hydrogels were also able to generate small electrical currents. Overall, these results show that mold assemblies presenting different surface properties can be employed to tune the electro-actuation responsiveness of ionic liquid-based soft actuators and lead to the development of engineering devices with a broad range of applications, including artificial muscles and tissue engineering scaffolds.

Electrophoretic Adhesion of Conductive Hydrogels.

For the development of next-generation wearable and implantable devices that connect the human body and machines, the adhesion of a conductive hydrogel is required. In this study, a conductive hydrogel is adhered using an electrophoretic approach through polyion complex formation at the interface of the hydrogels. Cationic and anionic conductive hydrogels adhere to anionic and cationic hydrogels, respectively. Moreover, the cationic and anionic conductive hydrogels adhere strongly to each other and the adhered conductive hydrogels exhibit conductivity. De-adhesion is possible by adding a salt and re-adhesion is demonstrated under aqueous conditions. It is believed that this innovative adhesion strategy for conductive hydrogels will be a fundamental technology for the connecting "soft" people and "hard" machines.

Tuning the crosslink structure of cationic hydrogel for enhanced chromium(VI) removal: The covalent and electrostatic co-crosslinked effects and adsorption mechanism

Elevated chromium(VI) (Cr(IV)) concentrations in drinking water or ground water can pose a public health concern. In this study, layered double hydroxides-isethionate (LDH-ise) assisted covalent and electrostatic co-crosslinked cationic hydrogel (CH-LDH-ise) was prepared as a potential adsorbent for Cr(VI) removal from aqueous solution. The scanning electron microscopy and X-ray diffraction results indicated that the LDH-ise sheets were exfoliated and crosslinked with the 3-(Acryloylamino) propyltrimethylaminium chloride (APTMACL) polymer chains. The adsorption of Cr(VI) onto the CH-LDH-ise was highly pH-dependent, and the removal efficiency by CH-LDH-ise composites was much higher than the CH (no crosslinker). The adsorption kinetic followed a pseudo-second-order, and reached equilibrium within 2 h. The corresponding maximum Cr(VI) adsorption capacity of CH-LDH-ise was 408.4 mg/g at the equilibrium concentration of 364.4 mg/L. The enhanced adsorption of Cr(VI) was also achieved in the presence of competing anions (including Cl−, NO3−, SO42−, HCO3−, SiO44−, and HA). Moreover, the in situ regeneration/recycle results implied the column adsorption capacity of CH-LDH-ise was 2250 bed volumes as the concentration of Cr(VI) decreased from 2.5 mg/L to 0.1 mg/L (The US drinking water standard for total chromium) at empty bed contact time = 6 min, and slightly decreased in the second recycle. The combination analysis of in situ Fourier transform infrared, in situ Raman, X-ray photoelectron spectra, and electron paramagnetic resonance revealed that the Cr(VI) capture mechanism was dominated by the electrostatic interactions and hydrogen bonding effect - the sources of the –N+(CH3)3 and –NH groups in CH-LDH-ise, respectively.

Cationic superabsorbent hydrogel composed of mesoporous silica as a potential haemostatic material.

The control of massive bleeding and its related wound infection is the main challenge for both military and civilian trauma centres. In this study, a cationic superabsorbent hydrogel coordinated by mesoporous silica (CSH-MS) was synthesized by free-radical polymerization for both haemostasis and antibacterial use. The as-prepared CSH-MS has a rough surface, and its water absorption is approximately 5000%. The resultant CSH-MS1 could promote blood cell aggregation and facilitate plasma protein activation via haemadsorption, resulting in efficient blood clot formation. Furthermore, CSH-MS1 (with approximately 5.06% contents of MS) dramatically reduces bleeding time and reduces blood loss in a rat-tail amputation model. Moreover, the CSH-MSs exhibits good antibacterial activities, excellent cytocompatibility and negligible haemolysis. Therefore, CSH-MS can serve as a novel type of haemostatic material in clinical applications.

Nitrate removal from aqueous solutions by magnetic cationic hydrogel: Effect of electrostatic adsorption and mechanism

Excessive nitrate (NO3−) is among the most problematic surface water and groundwater pollutants. In this study, a type of magnetic cationic hydrogel (MCH) is employed for NO3− adsorption and well characterized herein. Its adsorption capacity is considerably pH-dependent and achieves the optimal adsorption (maximum NO3−-adsorption capacity is 95.88 ± 1.24 mg/g) when the pH level is 5.2–8.8. The fitting result using the homogeneous surface diffusion model indicates that the surface/film diffusion controls the adsorption rate, and NO3− approaches the center of MCH particles within 30 min. The diffusion coefficient (Ds) and external mass transfer coefficient (kF) in the liquid phase are 1.15 × 10−6 cm2/min and 4.5 × 10−6 cm/min, respectively. The MCH is employed to treat surface water that contains 10 mg/L of NO3−, and it is found that the optimal magnetic separation time is 1.6 min. The high-efficiency mass transfer and magnetic separation of MCH during the adsorption–regeneration process favors its application in surface water treatment. Furthermore, the study of the mechanism involved reveals that both –N+(CH3)3 groups and NO3− are convoluted in adsorption via electrostatic interactions. It is further found that ion exchange between NO3− and chlorine occurs.

Enhanced photocatalytic hydrogen production of CdS embedded in cationic hydrogel

In this study, we describe the successful fabrication of CdS in ionic hydrogels by an in situ growth method and demonstrate that the as-prepared CdS in hydrogels (CdS/HGel) can be used as cost-effective and recyclable catalysts for photocatalytic hydrogen generation. The structure and morphology of CdS/HGels were characterized by various techniques including X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy. The resultant CdS in cationic hydrogel (CdS/HGelPDAM2) showed the best performance of photocatalytic hydrogen production and the hydrogen production rate was up to 10.35 or 7.70 mmol h−1 g−1 when triethanolamine or Na2S–Na2SO3 was used as sacrificial agent. However, CdS in anionic hydrogel (CdS/HGelPAAM) showed poor photocatalytic hydrogen production performance under the same conditions. The solution pH and sacrificial agent type are also indispensable factors that affect the photocatalytic hydrogen production. The enhancement of hydrogen production comes from interaction between polymer chains and Cd2+, high dispersibility of CaS nanoparticles in hydrogels, high hydrophilic and swelling ability of hydrogel, high diffusion rate of reactant in hydrogel, and inhibited binding possibility of photogenerated electron-hole pairs. Since CdS/HGelPDAM has excellent hydrogen production efficiency and ease recovery property, it will be a potential photocatalyst for photocatalytic reactions.

An Overview of Simulated Hydrogel Behaviour under Various Kinds of Stimulation

AbstractPolyelectrolytic gels placed in aqueous solution show effects under various kinds of stimulation. The stimuli could be e.g. of chemical, electrical, mechanical or thermal nature. The hydrogels react via uptake or delivery of mobile ions and solvent, and they show enormous swelling capabilities. This multifunctional behaviour is potentially attractive for chemo‐electro‐mechanical energy converters or for the use as actuators or sensors. In the present research, anionic and cationic hydrogels are investigated, which means that the polymer network contains anionic or cationic bound charged groups. The chemical stimulation is applied by a change of boundary conditions in the solution bath for the salt concentrations. The electrical stimulus is realized by incorporating electrodes between which an electric potential difference is applied. The mechanical stimulus is realized by prescribed displacements at a boundary of the hydrogel itself. The thermal stimulus is applied as transient temperature change over the whole domain, incorporating temperature‐dependent material parameters and osmotic pressure differences. The reactions of the hydrogel differ depending on the sensitivity of the gel to the applied stimulus. The incorporated chemo‐electro‐mechanical model enhanced with thermal dependencies is capable of giving local concentrations, electric potential and mechanical displacements.