Anionic Hydrogels Research Articles

A diode-like integrated hydrogel for piezoionic generators and sensors

Wearable sensing electronic devices based on hydrogel are gradually developing towards multifunction and portability, however, efficiently harvesting energy from the surrounding environment to power traditional hydrogel-based wearable electronic devices is a major challenge. The assembly of multilayer heterogeneous hydrogels is a potential strategy to address this challenge. Herein, inspired by the structure of diodes, a diode-like integrated hydrogel composed of a three-tier structure of anionic polyelectrolyte hydrogel, polyacrylamide hydrogel and cationic polyelectrolyte hydrogel is developed. By the connection of polyacrylamide hydrogel, the composite hydrogel exhibits excellent structural stability and mechanical properties. Notably, due to the introduction of MXene ion-conducting microchannels, the directional transport of free cations and anions ionized by anionic and cationic polyelectrolytes is achieved, thereby improving the conductivity (74.58 mS/cm), sensing (gauge factor = 7.47) and piezoionic output performance of the composite hydrogel. The composite hydrogel-based sensor can sense tiny facial movements and recognize the direction of human movement, and the composite hydrogel-based piezoionic generator exhibit more efficient mechanical-electric conversion performance, which can output the maximum voltage of 1410mV, current of 28 μA, and power density of 2.9mW/m2 for a composite hydrogel of 5×5 cm2. The integration of multilayer heterogeneous hydrogels proposes a versatile strategy for the development of high-performance hydrogel-based self-powered sensing electronic devices, expanding the application of hydrogels in artificial intelligence and human-computer interaction.

Swelling Behavior of Anionic Hydrogels: Experiments and Modeling.

Polyelectrolyte hydrogels are smart materials whose swelling behavior is governed by ionizable groups on their polymeric chains, making them sensitive to pH and ionic strength. This study combined experiments and modeling to characterize anionic hydrogels. Mechanical tests and gravimetric analyses were performed to track hydrogel mass over time and at a steady state under varying pH and salt concentrations. The swelling ratio exhibited a bell-shaped curve with pH, reaching 120 in pure water, and decreased with increasing salt concentrations. Transient regimes showed slower swelling (~40 h) under pH stimulation compared to faster deswelling (~20 h) induced by salt. A fully coupled model integrating mass transport and solid mechanics was developed, with solvent diffusivity as the sole adjustable parameter in transient simulations. In conclusion, this study combined experiments and modeling to uncover complex mechanisms in PE behavior under two external stimuli, providing insights essential for designing advanced hydrogels.

Spatiotemporally Controllable Chemical Delivery Via Hydrogel Electroosmotic Pump

Objectives Chemical delivery is an important basic operation in various biomedical fields, including in vitro cell analysis for drug development and in vivo drug management using implanted and wearable devices.[1] Traditional controllable drug delivery system (DDS) uses pressure-driven microfluidics and external pressure pumps to apply water pressure to the nozzles of microchannels, which makes it hard to instantaneously transmit pressure via flexible soft microchannels, resulting in low controllability of chemical transportation.[2] EOF is a solvent convection motion generated by the preferential electrophoretic movement of mobile counter cations (or anions) through negatively (or positively) charged microchannels (Fig. 1a). In this regard, the EOF-based DDS is electrically controlled and multifunctional, enabling the transportation of most chemicals, regardless of their charge and size.[3] Although some of the established EOF-based pumps used porous materials sandwiched between electrodes to prevent current from flowing to the outside, one of the electrodes is close to the target, which raises concerns about the impact of electrolysis. In addition, many traditional electroosmotic pumps have external electrodes, and the drug transportation may be accompanied by unnecessary electrical stimulation of target cells and tissues.[4] In this study, we developed an EOF-driven chemical delivery system generated by the combination of anionic and cationic hydrogels, as shown in Fig. 1b. Since the EOF directions in anion hydrogel (A-hydrogel) and cationic hydrogel (C-hydrogel) are opposite due to the cations and anions that preferentially move, the enhanced EOF at the outlet of the device can effectively transport chemicals without any external ion current. Results and Discussion Utilizing the inherent flexibility and water-retentive properties of the hydrogel, two slender tubular delivery devices (in straight state and tied state respectively) were fabricated to enable insertion into intricate in vivo structures. As illustrated in Fig . 1c, the EOF rate, discerned as the linear slope of the plots, was assessed under ± 0.5 mA current conditions for both the straight (blue plot) and tied (red plot) states. The flow rates exhibited negligible disparity between the two states during both injection and suction maneuvers. These findings underscore the remarkable adaptability of the developed thin-film device, capable of accommodating the substantial deformations requisite for precise localized drug delivery within complex organ structures. Fig . 1d shows the assessment of rhodamine B (RhB) ejection into 0.3 wt% agarose hydrogel cubes, selected for its resemblance to brain tissue properties. Notably, the quantity of RhB ejected into the agarose medium exhibited a discernible correlation with applied currents ranging from 0 to 0.3 mA, suggesting the application potential for controlled in vivo chemical dispensation. Conclusion In this study, a novel concept of a chemical delivery system by focusing on the EOFs generated in the A- and C-hydrogels in opposite directions from each other was introduced. The utilization of A/C-hydrogel combinations in the construction of tubular devices facilitated the creation of a closed-loop system for the generation of ionic current. This unique design characteristic allowed for chemical delivery to target cells and tissues without reliance on external flows of ion current. This feature is important, as it extends beyond muscles and nerves to encompass an array of cell and tissue types that can respond to ionic currents. Moreover, the versatility of EOF-based systems is underscored by their applicability to a diverse range of chemicals, irrespective of their charge and size. This inherent adaptability lends considerable practical advantages to EOF-based DDS, enhancing their utility across various biomedical applications. Reference A. Antos, D. Liu, H. Zhang, Microfluidics for Pharmaceutical Applications: From Nano/Micro Systems Fabrication to Controlled Drug Delivery, Elsevier, New York 2019.Minev, P. Musienko, A. Hirsch, Q. Barraud, N. Wenger, E. M. Moraud, J. Gandar, M. Capogrosso, T. Milekovic, L. Asboth, R. F. Torres, N. Vachicouras, Q. Liu, N. Pavlova, S. Duis, A. Larmagnac, J. Vörös, S. Micera, Z. Suo, G. Courtine, S. P. Lacour, Science 2015, 347, 159J. Pikal, Adv. Drug Deliv. Rev. 2001, 46, 281L. Snyder, J. Getpreecharsawas, D. Z. Fang, T. R. Gaborski, C. C.Striemer, P. M. Fauchet, D. A. Borkholder, J. L. McGrath, Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 18425 Fig . 1 (a) Schematic illustration of electroosmotic flow. (b) Schematic of EOF-driven chemical delivery system combined of anionic and cationic hydrogels. (c) EOF flow rate in the straight state (blue plot) and tied state (red plot) at ± 0.5 mA. (d) Demonstration of RhB delivery into 0.3 wt% agarose hydrogel by applying currents ranging from 0 to 0.3 mA for 10 min. Figure 1

Application of Anionic Hydrogels from Date Palm Waste for Dye Adsorption in Wastewater Treatment.

This work aimed to develop an anionic cellulose nanofiber (CNF) bio-adsorbent from date palm tree waste and to investigate its removal efficiency compared to cationic methylene blue dye from contaminated water. Date palm pulp was first prepared from date palm leaves through acid hydrolysis using H2SO4, followed by hydrolysis in a basic medium using KOH, in which the process completely removed the components of hemicellulose, lignin, and silica. To obtain anionic CNF, the resulting pulp was further treated with H2SO4, followed by centrifugation. Biogel formation of the CNF suspension was promoted by sonication, where its removal efficiency of methylene blue dye was studied as a function of dye concentration, temperature, contact time, and pH value. In this work, we investigated two isotherms, i.e., Langmuir and Freundlich. The Langmuir model's consistency with the experimental data suggests that the adsorption of methylene blue dye onto CNF is monolayer and surface-limited. The reported maximum removal efficiency of 5 mg/g at 60 °C indicates the optimal temperature for adsorption in this specific case. Additionally, a pseudo-second-order model and Elovich model were also utilized to obtain a better understanding of the adsorption mechanism, in which we found not just physical adsorption but also an indication of a chemical reaction occurring between methylene blue dye and CNF. According to the results, that pseudo-second-order model's consistency with the experimental data suggests that the adsorption of methylene blue (MB) onto CNF is rate-limiting step involving chemisorption between the two. The study reveals that CNF adsorbents derived from renewable natural waste sources such as date palm leaves can be effective in removing cationic contaminants such as methylene blue dye.

PH Sensitive Dual Cross‐Linked Anionic and Amphoteric Interpenetrating Network Hydrogels for Adsorptive Removal of Anionic and Cationic Dyes

AbstractThe contamination of water by organic dye compounds are worldwide environmental problem due to their highly toxic nature. To address this environmental issue, a simple technique with highly efficient dye removal was developed to prepare pH‐ sensitive dual‐crosslinked anionic and amphoteric interpenetrating network (IPN) hydrogels based on Na‐carboxymethyl cellulose (Na‐CMC) using jute stick‐based cellulose. Crosslinked Na‐CMC and crosslinked κ‐carrageenan (KC) were interlaced by H‐bonding in anionic IPN hydrogel (An‐gel), but crosslinked Na‐CMC and crosslinked Chitosan (CS) were interlaced by electrostatic interaction in amphoteric IPN hydrogel (Am‐gel). In various operating conditions (pH, temperature, etc.) An‐gel displayed a higher number of swelling ratios of about 2560% at pH 7.2 and Am‐gel of about 1874% at pH 5.5. Based on the point of zero charge, An‐gel achieved the maximum removal efficiency of 81.62 % for methylene blue (MB) at pH 7.2, whereas Am‐gel achieved 85.38% removal efficiency for eosin yellow (EY) at pH 5.5. The adsorption kinetics of IPN hydrogels followed a pseudo‐second order model and best fitted by Langmuir isotherm model. The removal efficiency of MB and EY decreased slightly with increasing temperature. The values of ΔH°, ΔG°, and ΔS° indicated an exothermic, spontaneous, and disordered adsorption process.

Fundamental Studies on Fluids-Independent Regenerative Nanocomposite Hydrogels for Fracture Treatments of Conformance Control.

Traditional granular hydrogels showed excellent injectivity, thermal integrity, and efficient remediation of heterogeneous reservoirs. However, granular hydrogels have demonstrated their inability to adapt to fractures due to the lack of sufficient interactions. Herein, we present new nanocomposite hydrogels consisting of cationic nanogelators and anionic granular hydrogels that can chemically in situ reform bulk hydrogels in the fractures. Interestingly, our granular hydrogels showed recross-linking independence on carrying fluids, contrary to prior reported fluid-dependent recross-linking granular hydrogels. The recross-linking of nanogelators and granular hydrogels can be accomplished from room temperature to 130 °C. The nanocomposite hydrogels displayed increased shear elastic moduli compared to pristine anionic granular hydrogels, probably due to the increased covalent cross-links formed by the homogeneous regenerative approach. We found that the granular hydrogels had high salinity tolerance even in the presence of 1000 ppm divalent ions of calcium (Ca2+) since Ca2+ ions often act as the cross-linker for partially hydrolyzed acrylamide-based hydrogels. Overall, we obtained new regenerative nanocomposite hydrogels based on cationic nanogelators and anionic granular hydrogels for fracture treatments.

Synthesis and Characterization of Triticale Starch-Based Hydrogel for pH Responsive Controlled Diffusion.

Considering the FAO perspectives for agriculture toward 2030, many natural sources will be no longer profitable for the synthesis of many biomaterials. Triticale (X Triticosecale Wittmack) is a cereal crop synthesized to withstand those marginal conditions; however, it is primarily used as fodder worldwide. We reported for the first time the synthesis of a natural anionic hydrogel with gastrointestinal pH stimulus-response as a new alternative of smart material, based on Eronga triticale starch as sustainable biomass, using citrate (pK a ∼3.1, 4.7, and 6.4) as cross-linking agent. The scanning electron microscopy and X-ray diffraction exhibited A and B-type starch granules, and semicrystallinity A-type. The presence of the anionic sensing group (COOH) was verified by infrared spectroscopy, the interactions by hydrogen bonds between starch and glycerol and esterification between starch and citric acid were identified by 1H NMR spectra, and through thermal analysis hydrogels exhibited four endothermic curves (179-319 °C, ∼0.711-39 kJ/mol E a). The results showed that the slight addition of glycerol increases the thermal stability, but a higher amount of glycerol decreases the intermolecular forces affecting the thermal stability contrary, the mechanical properties could be benefited. The rheological analyses showed viscoelastic tendency (G' > G″) with high stability (Tanδ < 1) in frequency, time, and strain sweeps. Gastrointestinal pH sensitivity (∼2-7.8) was verified (α ≤ 0.01) following Fick's diffusive parameters, which resulted in a tendency to gradually release BSA with increasing pH ∼3-7 by anomalous and case-II diffusion, showing greater release at pH ∼7.8/3.5 h (80-96%). We aim to expand the biomaterials area focusing on triticale starch due to its limited reported investigations, low-cost, green modification, and its rheological performance as plastic.

Tailoring anionic solar evaporator with an enhanced Donnan effect for a highly effective salt resistance desalination and water purification

Emerging solar-driven interfacial water evaporation demonstrates immense potential in mitigating worldwide water shortages, offering exceptional solar-to-vapor conversion efficiency, off-grid operability, zero liquid discharge capability and low carbon footprint. A critical requirement for sustainable extraction clean water from brine is the development of solar evaporators with both salt resistance and high evaporation rates. In response to this demand, this research proposed an enhanced Donnan effect anionic solar evaporator through filling wood in situ with PVA/PAA hydrogel. The resulting anionic solar evaporator demonstrated broadband spectral absorption, excellent photothermal conversion, and water activation capability. Notably, based on the negative charge property of the –COO– group anionic hydrogel, it could enhance Donnan effect and restrict the diffusion of Cl− to the evaporator, ensure enduring salt resistance and stability in purifying brine effectively. Experiments proved that the anionic anionic solar evaporator attained a remarkable water evaporation rate of 2.439 kg m−2 h−1 during a desalination of 15 wt% NaCl solution under 1 kW m−2 solar radiation, and no obvious salt accumulation had been observed during prolonged evaporation processes. With high efficiency, renewability, deployability, low cost, and durability, the anionic solar evaporator emerges as a promising solution for mitigating water scarcity, especially in economically challenged regions and provides valuable perspectives for future investigations into the water-energy-climate nexus.

Investigation of the catalytic activity of Ag(0) nanoparticles supported into anionic hydrogel networks for hydrogen production process

In the presented study, the hydrogen production from the hydrolysis of the morpholine-borane (MB) with hydrogel supported Ag(0) nanoparticle catalyst system was reported. For this purpose, nanosized p(sulfopropyl acrylate potassium salt-co-itaconic acid)@Ag composite material, (p-SIH@Ag), was prepared and used as catalyst. In this study, the effects of base, catalyst amount, MB substrate concentration and temperature were investigated for the MB hydrolysis reaction. p-SIH@Ag catalyzed MB hydrolysis reaction at 30 °C, the activation energy (Ea) was determined as 24.3 kjmol−1 and the turn over frequency (TOF) as 37.52 mol H2(mol Ag(0).h)−1. In reusability studies, the catalyst preserved 72% of its activity even after the 5th catalytic cycle despite the sensitivity of Ag metal to oxidation. Our study is the first in the literature to use hydrogel supported Ag metal catalyst system in hydrogen production via MB hydrolysis.

Lean-water hydrogel electrolyte with improved ion conductivity for dendrite-free zinc-Ion batteries

Although rechargeable aqueous zinc-ion batteries (ZIBs) are regarded as promising energy storage devices, the uncontrollable Zn dendrite and undesirable side reactions severely limit their practical applications. Herein, an anionic hydrogel electrolyte PAM/SA with 3D porous structures is developed by integrating sodium alginate (SA) and polyacrylamide (PAM) networks for highly reversible Zn plating/stripping. Mechanically enhanced and lean-water PAM/SA hydrogel with anionic chains for constructing ionic channels and molecular lubrication films, which facilitate Zn2+ migration for a high ionic conductivity (5.4 S m−1) and Zn2+ transference number (0.86) even under lean-water conditions (about 60%). Based on the experimental and theoretical analysis, the SA chain with strong coordination ability endows PAM/SA with improved desolvation kinetics and the ability to regulate the electric field intensity at the electrode/electrolyte interface, which is beneficial for suppressing side reactions and facilitating directional Zn deposition. Subsequently, the symmetric Zn//Zn cell based on PAM/SA hydrogel electrolyte delivers stable cycles for over 1800 h. The assembled Zn//V2O5 battery based on PAM/SA reveals a high specific capacity and a long cycle life. This work provides a new insight for developing hydrogel electrolytes with high ionic conductivity and lean-water properties toward stable Zn anode

Fabrication of nanozyme-thixotropic anionic hydrogel coating with multi-enzyme-mimicking activity for the treatment of fungal keratitis

Fungal keratitis is the primary cause of infectious corneal blindness in China. Currently, early-stage treatment mainly involves the frequent administration of antifungal medications to ensure prolonged corneal contact and maintain effective drug concentration. This approach, however, may lead to harmful side effects and increased antifungal resistance due to the substantial use of antifungal agents. Consequently, the development of advanced antifungal strategies is essential. In the study, we fabricated a multi-enzyme-mimicking nanozyme-thixotropic anionic hydrogel coating (NHC) that incorporated voriconazole and copper-proanthocyanidins (CuPC) nanozyme, by the Schiff base reaction of self-synthesized polyaldehyde oligomer (PAO) with amino functionalized hyaluronic acid (AHA), for the treatment of fungal keratitis. The thixotropic anionic hydrogel significantly boosts the retention time and permeability of voriconazole, allowing a low dose to achieve a high therapeutic concentration. Additionally, the inherent antifungal and peroxidase-like activities of CuPC, coupled with the intrinsic characteristics of anionic hydrogel, further enhance the antifungal efficacy of NHC. Moreover, the NHC assists in corneal wound healing through stimulating cell proliferation by HA derivative as well as scavenging ROS via the catalase-like and superoxide dismutase-like activities of CuPC. The in vitro and in vivo studies have illustrated the safety and effectiveness of NHC, indicating its potential in the treatment of fungal keratitis.

Ultrasound-triggered in situ hydrogel formation for spinal disc repair

Over 600 million people suffer from lower back pain attributable to spinal disc degeneration. Treatments range from conservative physiotherapy to costly, invasive options like spinal fusion surgery. Injectable engineered materials may allow minimally invasive disc repair, but self-curing lacks process control, and optical in situ curing is depth-limited. We, therefore, propose ultrasound-triggered implant formation, enabling spatiotemporal control at clinically relevant tissue depths. We developed an anionic polysaccharide-based hydrogel, seeded with calcium-loaded thermosensitive liposomes. Focused ultrasound was used to heat this injectable precursor material to just above the lipid phase-transition temperature of 41 °C, inducing calcium release and ionically crosslinked network formation. Controlled heating was achieved by elevating the acoustic attenuation of the precursor solution with purified glass microspheres. The heating and gelation processes were controlled in real-time using thermometry and acoustic cavitation emissions. We optimized the ultrasound frequency and pressure amplitude to provide controlled heating with minimal cavitation. After these parameters were employed for ultrasound-mediated gelation, the rheological properties of the resultant gels were compared to literature values for native spinal disc material. Finally, in situ gel formation was evaluated in ex vivo bovine tail discs, from injection to mechanical assessments, confirming the ability to remotely trigger injectable disc-mimicking materials.

A facile cross-linking copolymerization strategy to synthesize anionic magnetic hydrogels for efficient removal of tylosin tartrate

The novel magnetic hydrogel adsorbents were prepared using a facile cross-linking copolymerization method and applied for the adsorption of tylosin tartrate. A series of characterization tests were conducted to investigate the functional group structure, thermal stability, surface morphology, and magnetic properties of the adsorbents. Furthermore, the influence of dosage, initial concentration of tylosin tartrate, adsorption time and pH value on the adsorption performance of the adsorbent were studied. Batch adsorption results demonstrated that Mag@GAS exhibited the highest adsorption capacity of 188.64 mg/g. Furthermore, the sulfonic acid groups on the surface of Mag@GAS showed minimal pH dependency, allowing for high adsorption capacity over a wide pH range. The zeta potential experiments investigated the adsorption mechanism of Mag@GAS towards TST under different pH values. The pseudo-second-order rate model described adsorption kinetics data well, indicating that adsorption process was mainly controlled by intra-particle diffusion and film diffusion. The adsorption isotherm data fitting using the Freundlich isotherm model showed good agreement. The results showed that the adsorption process of TST by Mag@GAS was a multilayered heterogeneous surface adsorption. The thermodynamic parameters indicated the spontaneous and endothermic adsorption. Additionally, regeneration experiments demonstrated that Mag@GAS was easily separable and effectively regenerated. Therefore, Mag@GAS shows great potential as an adsorbent.

PH-responsive prodrug containing Zr-based MOF and aldehyde-based drug; anionic hydrogel coating as a smart delivery system

In this work, a metal organic framework (MOF)-based prodrug was fabricated via Schiff base reaction between UiO-66-NH2 and 3,4-dihydroxybenzaldehyde (DHBD) drug to form DHBD@MOF prodrug containing pH-sensitive C=N bonding. Moreover, a dual pH-responsive drug delivery platform containing (5-Fluorouracil) 5-FU drug and DHBD@MOF prodrug entrapped by carboxymethyl cellulose (CMC) and alginate (Alg.) hydrogel (DHBD@MOF/5-FU@CMC/Ca2+/Alg.) was developed. Then, the characteristics of prodrug and delivery system were analyzed using PXRD, FT-IR, FE-SEM, TEM,and BET techniques. The in vitro and cumulative release results revealed that the fabricated platform was protected successfully by hydrogel from burst release in acidic condition of stomach and small intestine so that 1.31% release of DHBD from DHBD@MOF/5-FU@CMC/Ca2+/Alg was recorded after 2.5 h at pH 1.2, while DHDB release from DHBD@MOF prodrug (without hydrogel) was about 90% after 2.5 h at pH 1.2. The synthesized hydrogel could control the release of drug in a smart controlled manner at specific sites so that after hydrogel swelling at intestine and colorectum at pH around 6.5–7.4 and prodrug release, pH-sensitive C=N bonding of DHBD@MOF is cleaved at acidic colorectum cancer sites, and the inactive prodrug is efficiently activated. The hydrogel could successfully control the release of DHBD and 5-FU in SGF (simulated gastric fluid, at different pHs) from DHBD@MOF/5-FU@hydrogel at different pHs of 1.2, 4.5, 7.4 and 6.5, so that the gradual release of DHBD from DDDS in intestine (pH 7.4) and colorectum (pH 6.5) after 8.5 h and 24 was 10.60 and 41.68%, respectively, where 89.40 and 58.32% of inactive DHDB@MOF prodrug after 8.5 and 24 h could access to the acidic tumors (cancer sites). The findings of this research can be applied for medical science and pharmaceutics after completing the in vivo experiments.

Zincophilic Anionic Hydrogel Electrolyte with Interfacial Specific Adsorption of Solvation Structures for Durable Zinc Ion Hybrid Supercapacitors

AbstractThe rechargeable zinc ion hybrid supercapacitors (ZHSCs) are critically hindered by the low Coulombic efficiency and poor lifespan due to the continuous water‐induced side reactions and uncontrolled dendrite growth of the Zn anode. Herein, a zincophilic anionic hydrogel electrolyte (PSCA/Zn(OTf)2) is constructed by incorporating the dodecyl sulfate anions ((OSO3R)−) micelles to manipulate the solvation structures of Zn2+ cations via the moderate ion–ion coordination interactions for manipulating the Zn deposition behavior and interfacial chemistry on Zn electrode. Joint experimental and theoretical results show that the constructed solvated Zn2+ cations with the ionized (OSO3R)− electron donor significantly restrict the occurrence of adverse reactions (hydrogen evolution reactions). Concomitantly, the newly involved (OSO3R)− anions influence the adsorption configurations of solvated Zn2+ ions, which alter the electrocrystallization patterns for dendrite‐free growth and induce the oriented deposition for rapid reaction kinetics of Zn electrodes. As a proof of concept, the Zn||Zn symmetric cells with PSCA/Zn(OTf)2 exhibit high reversibility for deposition/stripping behavior with an extended long cycle span. Significantly, benefiting from the synergy of the modulatory electrolyte environment and the regulated adsorption configurations, a quasi‐solid‐state Zn||PSCA/Zn(OTf)2||N‐doped porous carbon material (NPC) ZHSC exhibits exceptional cycling stability for over 40 000 cycles with a low capacity decay (0.00027% per cycle).

Regulated the Swelling Properties of Poly(acrylamide‐co‐acrylic acid) Hydrogel by Changing the Charge Density

AbstractHydrogels can swell without dissolving in water and are widely used in water treatment and biomedicine. The swelling rate of hydrogels is closely related to the network structure and charge density of hydrogels, but there are few detailed studies in this area. In this work, poly(acrylamide‐co‐acrylic acid) anionic hydrogel with acrylic acid (AA) as anionic monomer is prepared. By changing the monomer ratio, or changing the pH value of hydrogels, the internal charge density can be adjusted, and then the swelling rate can be controlled. With the increase of AA monomer content, the content of carboxylate in hydrogel increases, resulting in higher charge density. A high charge density corresponds to a high swelling rate. On the other hand, the swelling rate is closely related to the pH value, which is because the concentration of proton affects the ionization of carboxylic acid, which leads to the change of charge density. It is worth noting when pH increases to 10, the charge shielding effect of the counter‐ion (Na+) gradually increases, thus limiting the swelling of the hydrogel and reducing the swelling rate. This work has reference value for the practical application of hydrogels.

Spatiotemporally Controllable Chemical Delivery Utilizing Electroosmotic Flow Generated in Combination of Anionic and Cationic Hydrogels

AbstractSpatiotemporally controlled chemical delivery is crucial for various biomedical engineering applications. Here, a novel concept of electrically controllable delivery utilizing electroosmotic flow (EOF) generated in a combination of anionic and cationic hydrogels (A‐ and C‐hydrogels) is reported. The unique advantages of the A/C‐hydrogel combination are demonstrated utilizing a flexible sheet‐shaped and a thin tubular devices. Since the directions of EOF in the A‐ and C‐hydrogels are opposite to each other, the ionic current for EOF generation flows inside the delivery devices, enabling chemical delivery without accompanying external ionic current that could stimulate target cells and tissues. A thin tubular device, which can be inserted into narrow in vivo structures and be integrated with other flexible devices, exhibits high robustness and repeatability thanks to the flexibility and water retentivity of hydrogels. The EOF devices with A/C‐hydrogels combination show high controllability superior to the pumping with a conventional syringe; the volumetric flow rate is able to be controlled proportionally to the current applied, for example, ≈0.4 µL (mA min)−1 for the tubular device. The developed EOF‐based devices are versatile for delivery of most chemicals regardless of their charge and size, and have great potential for both biomedical researches and therapeutics.

Novel hydrogel poly (GG-co-acrylic acid) for the sorptive removal of the color Rhodamine-B from contaminated water

Textile effluent's treatment is highly desired due to the presence of hazardous, water-soluble and non-biodegradable dyes that not only have harmful effect on the environment but on living beings as well. Treatment of these pollutants by sorption through biosorbents is considered to be a best method of choice due to greener nature of the processes. In this connection hydrogel sorbents might be an intriguing option due to its straightforward application, great efficacy, easy synthesis, rapid turnaround, and potential of recycling. Herein, novel hydrogel was prepared using Gellan Gum and acrylic acid (GG-co-AAc) which were then characterized by instrumental techniques like UV/visible and FTIR spectroscopy, SEM, EDX and XRD. The anionic hydrogel's adsorption capacity, swelling behavior, and sorption potential were determined using Rhodamine-B as potential environmental pollutant. The hydrogel exhibited an impressive adsorption capacity of 1250 mg/g. Swelling experiments were performed in Milli-Q distilled water at different pH levels, reaching maximum swelling of 3230% after 23 h as determined through Fickian diffusion. At pH 7, the anionic hydrogel's sorption potential was thoroughly studied in the subsequent experiments. The adsorption process was found to follow the Langmuir isotherm, indicating a monolayer adsorption mechanism supported by higher R2 values compared to the Freundlich isotherm. Thermodynamic analysis revealed the exothermic nature of the adsorption process, with a negative enthalpy value of −11371 KJmol-1 and negative entropy value of −26.39 Jmol−1K−1, suggesting a less ordered system. These findings provide valuable insights into the adsorption characteristics and potential applications of the synthesized anionic hydrogel.

Arrhenius-model-based degradable oligourethane hydrogels for controlled growth factor release.

Biodegradable hydrogels are growing in demand to enable the delivery of biomolecules (e.g. growth factors) for regenerative medicine. This research investigated the resorption of an oligourethane/polyacrylic acid hydrogel, a biodegradable hydrogel which supports tissue regeneration. The Arrhenius model was used to characterize the resorption of the polymeric gels in relevant in vitro conditions, and the Flory-Rehner equation was used to correlate the volumetric swelling ratio with the extent of degradation. The study found that the swelling rate of the hydrogel follows the Arrhenius model at elevated temperatures, estimating degradation time in saline solution at 37°C to be between 5 and 13 months, serving as a preliminary approximation of degradation in vivo. The degradation products had low cytotoxicity towards endothelial cells, and the hydrogel supported stromal cell proliferation. Additionally, the hydrogels were able to release growth factors and maintain the biomolecules' bioactivity towards cell proliferation. The study of the vascular endothelial growth factor (VEGF) release from the hydrogel used a diffusion process model, showing that the electrostatic attraction between VEGF and the anionic hydrogel allowed for controlled and sustained VEGF release over three weeks. In a rat subcutaneous implant model, a selected hydrogel with desired degradation rates exhibited minimal foreign body response and supported M2a macrophage phenotype, and vascularization. The low M1 and high M2a macrophage phenotypes within the implants were associated with tissue integration. This research supports the use of oligourethane/polyacrylic acid hydrogels as a promising material for delivering growth factors and supporting tissue regeneration. STATEMENT OF SIGNIFICANCE: There is a need for degradable elastomeric hydrogels that can support the formation of soft tissues and minimize long-term foreign body responses. An Arrhenius model was used to estimate the relative breakdown of hydrogels, in-vitro. The results demonstrate that hydrogels made from a combination of poly(acrylic acid) and oligo-urethane diacrylates can be designed to resorb over defined periods ranging from months to years depending on the chemical formulation prescribed by the model. The hydrogel formulations also provided for different release profiles of growth factors, relevant to tissue regeneration. In-vivo, these hydrogels had minimal inflammatory effects and showed evidence of integration into the surrounding tissue. The hydrogel approach can help the field design a broader range of biomaterials for tissue regeneration.

Synthesis and Evaluation of Functionalized Polyurethanes for pH-Responsive Delivery of Compounds in Chronic Wounds.

Chronic wounds, depending on the bacteria that caused the infection, can be associated with an extreme acidic or basic pH. Therefore, the application of pH-responsive hydrogels has been instigated for the delivery of therapeutics to chronic wounds. Herein, with the aim of developing a flexible pH-responsive hydrogel, we functionalized hydrophilic polyurethanes with either cationic (polyethylene imine) or anionic (succinic anhydride) moieties. A comprehensive physicochemical characterization of corresponding polymers was carried out. Particularly, when tested in aqueous buffers, the surface charge of hydrogel films was closely correlated with the pH of the buffers. The loading of the cationic and anionic hydrogel films with various compound models (bromophenol blue; negatively charged or Pyronin Y; positively charged) showed that the electrostatic forces between the polymeric backbone and the compound model will determine the ultimate release rate at any given pH. The potential application of these films for chronic wound drug delivery was assessed by loading them with an antibiotic (ciprofloxacin). In vitro bacterial culturing was performed using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Results showed that at the same drug dosage, different release profiles achievable from cationic and anionic polyurethanes can yield different degrees of an antibacterial effect. Overall, our results suggest the potential application of cationic and anionic hydrophilic polyurethanes as flexible pH-responsive materials for the delivery of therapeutics to chronic wounds.