Poly(N-isopropylacrylamide)-based ionic hydrogels: synthesis, swelling properties, interfacial adsorption and release of dyes

Facile Synthesis of Bioactive Silver Nanocomposite Hydrogels with Electro-Conductive and Wound-Healing Properties

Bioactive metal and metal oxide-based nanocomposite hydrogels exhibit significant antibacterial properties by interacting with microbial DNA and preventing bacterial replication. They offer potential applications as coating materials for human or animal skin injuries to prevent microbial growth and promote healing. In this study, silver nanoparticles (AgNPs) were synthesized using a chemical reduction method and incorporated into a polymer network to fabricate silver nanocomposite hydrogels (AgNCHGs) through a simple free radical polymerization method. N-isopropylacrylamide (NIPA), which has lower critical solution temperature (LCST) at about body temperature, or acrylamide (AAm) was used as the main monomer, while one or more ionic co-monomers, such as acrylic acid (AAc) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS), were incorporated to obtain AgNCHGs. AgNPs were introduced into the hydrogel network via three different approaches. In the first method, the synthesized hydrogel was immersed in a silver nitrate (AgNO3) solution and reduced in situ using sodium borohydride (NaBH4) as a reducing agent. The second method involved mixing AgNO3 with gel precursors before reduction with NaBH4 to form AgNPs within the hydrogel. The final approach synthesized the AgNCHGs directly in a dispersion of pre-fabricated AgNPs. The incorporation of AgNPs in different AgNCHGs was confirmed through various characterization techniques. Varying temperature and pH conditions can trigger the release of bioactive AgNPs from the hydrogels. Furthermore, the antimicrobial and wound-healing properties of the AgNCHGs were evaluated against bacteria and fungi, demonstrating their potential in biomedical applications. In addition, AgNCHGs exhibit excellent electrical conductivity. The electrical conductivity of the hydrogels can be finely tuned by adjusting the concentration of AgNPs, making these materials promising candidates for energy, sensor, and stretchable electronics applications. This study presents facile synthesis methods of AgNCHGs, which integrate bioactivity, wound healing, and electrical conductivity in the same matrix, addressing a significant challenge in designing multifunctional hydrogels for next-generation technologies.

Adsorption of methyl orange and methylene blue from aqueous solutions on pure bentonite: statistical physical modeling provides an analytical interpretation

This study investigates the adsorption of methylene blue (MB) and methyl orange (MO) dyes from aqueous solutions using purified Moroccan bentonite, being mainly composed of silica and alumina, in the form of quartz and cristobalite. The temperature controls the adsorption capacity for the kinetics, increasing 5.08% (from 295.1 to 310.1 mg/g) for the MB and 55.47% (from 86.8 to 134.9 mg/g) for the MO. It was discovered that the pseudo-second-order model, with a low Bayesian criterion indicator of 12.72 and R2adj > 0.996, was the best suitable for explaining both systems. The adsorption isotherm, experimental data indicate that both systems follow the Langmuir isotherm. At lower temperatures, 298.15 K 1.22 molecules are adsorbed per site. However, at a higher temperature of 328.15 K, the number of molecules is less than a unit of 0.68. As for MO, the number of molecules remains above 1.4 per site for all the temperatures studied. The endothermic nature of the system is indicated by the observation that the adsorption energy tends to grow for both systems: for the MB, it increases from 18.85 to 21.26 kJ/mol, and for the MO, it increases from 14.83 to 19.01 kJ/mol. Last, thermodynamic functions indicate that maximum entropy is reached around the half-concentration saturation at 25 and 124 mg/L, which is the maximum energetic concentration of the system. The same results were obtained for Gibbs free energy, where the maximum energy found was - 5.39 × 10-18 kJ/mol for the MB and - 1.99 × 10-18 kJ/mol for the MO at 328.15 K.

Fabrication and evaluation of smart pH/thermo dual-responsive injectable intratumoral in situ depot hydrogels for controlled 5-FU delivery

Background

5-FU has multiple applications in various cancers but has limitations owing to its shorter half-life and rapid metabolism. In this study, injectable intratumoral gels were developed to enhance 5-FU concentrations in tumor vicinity. Sterile tunable poly (N-isopropylacrylamide)-based pH/thermo dual-sensitive self-assembled and in situ crosslinkable injectable depot gels with low viscous grade of chitosan (LVCS) were developed via cold and free radical polymerization method for localized and sustained delivery.

Results

Rheological analysis confirmed the gelation temperature, sol–gel transitions and viscoelastic behavior of in situ gels. Swelling–deswelling–reswelling cycles established the effect of temperature on structural changes. Swelling tests and in vitro drug release conducted in various dissolution media at variable temperatures confirmed pH/thermal dual response of formulations. Methyl thiazolyl tetrazolium assay confirmed that the hydrogels have good cytocompatibility with above 85% cells viability in Vero cells. In vitro cytotoxicity assay against MCF-7 cells displayed that 5-fluorouracil has good anticancer activity in loaded gel form as compared to free 5-FU. The cytotoxic studies showed that IPLVCS-2 and IPLVCS-6 have the highest inhibition (IC50 = 47 ± 1 µg/ml, 34 ± 17 µg/ml) as compared to free 5-FU (IC50 = 52 ± 3 µg/ml).

Conclusion

Current findings conclude that taking the advantage of physiologic environment acidic pH and high temperature of cancer cells, poly(NIPAAm)-g-LVCS formulations can effectively be used as intratumoral controlled depot of 5-FU.

Graphical Abstract

Ionic Liquid Cross-Linked High-Absorbent Polymer Hydrogels: Kinetics of Swelling and Dye Adsorption

The use of polymer gels for the removal of toxic chemicals from wastewater is an important area in terms of both academic and industrial research. This work presents a simple approach to the fabrication of chemically cross-linked cationic hydrogel adsorbents using designed ionic liquid-based cross-linkers and their successful use in the removal of organic dyes. Two different ionic liquid cross-linkers, [VIm-4VBC][Cl] (ILA)/[DMAEMA-4VBC][Cl] (ILB), are synthesized by the simple nucleophilic substitution reaction of 4-vinylbenzyl chloride (4VBC) separately with 1-vinylimidazole (VIm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Cross-linked poly(acrylamide) (CPAam) and poly(2-hydroxyethyl methacrylate) (CPHEMA) hydrogels are then prepared from the corresponding monomers and as-synthesized cross-linkers (ILA and ILB) by free radical polymerization in the presence of a redox initiator combining ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED). The dried CPAam and CPHEMA xerogels exhibit macroporous morphology and high thermal stability. The hydrogel samples exhibit high swelling behavior, and the diffusion of water molecules into the hydrogels follows pseudo-Fickian kinetics. The cationic cross-linking sites in the hydrogel networks allow preferable binding with anionic dyes, and these dye uptake capacities are determined using different model anionic dyes via UV-vis spectroscopy. The dye adsorption onto these hydrogels follows a pseudo-second-order kinetic model. The adsorption mechanism is also analyzed by employing intraparticle diffusion and Boyd kinetic models. The relationship between the maximum equilibrium adsorption capacity (q_m) of the hydrogels for eosin B (EB) dye and the equilibrium EB concentration can be better described by Langmuir and Freundlich isotherm models, and the estimated q_m using the Langmuir isotherm can reach more than 100 mg g^-1. The cross-linked hydrogels can be easily regenerated and have a recycling efficiency of >80% for up to three consecutive dye adsorption-desorption cycles, which is promising for their use in wastewater treatment.

Poly(N-isopropyl acrylamide)-co-poly(sodium acrylate) hydrogel for the adsorption of cationic dyes from aqueous solution

In this study, we used radical polymerization to create poly (N-isopropyl acrylamide)-co-poly (sodium acrylate) [PNIPAM-co-PSA] hydrogels and analyzed the resulting products. N, N'-Methylenebisacrylamide was employed as a cross-linker, ammonium persulfate as an initiator, and N,N'-isopropyl acrylamide and sodium acrylamide as monomers. Structural analysis was measured by using FT-IR. Indeed, SEM analysis was used to characterize the morphological structure of the hydrogel. Studies on swelling were also done. The Taguchi approach was used to study and assess the adsorption studies of the hydrogels for the efficient removal of malachite green and methyl orange. For the optimization, a central composite surface methodology was applied. The effect of several parameters, including adsorbent dosage, pH, initial dye concentration, temperature, time, and mixing speed, was examined using the Taguchi technique, and the primary factors were chosen and examined using the central composite surface methodology. It was discovered that MG dye's (cationic) removal efficiency was higher than that of MO dye's (anionic). The results suggest that [PNIPAM-co-PSA] hydrogel can be used as an effective, alternative and promising adsorbent to be applied in the treatment of effluents containing the cationic dyes from wastewater. The synthesis of hydrogels provides a suitable recyclability platform for the adsorption of cationic dyes and allows for their recovery without the use of powerful reagents.

Dynamic Covalent Hydrogels: Strong yet Dynamic

Hydrogels are crosslinked polymer networks with time-dependent mechanical response. The overall mechanical properties are correlated with the dynamics of the crosslinks. Generally, hydrogels crosslinked by permanent chemical crosslinks are strong but static, while hydrogels crosslinked by physical interactions are weak but dynamic. It is highly desirable to create synthetic hydrogels that possess strong mechanical stability yet remain dynamic for various applications, such as drug delivery cargos, tissue engineering scaffolds, and shape-memory materials. Recently, with the introduction of dynamic covalent chemistry, the seemingly conflicting mechanical properties, i.e., stability and dynamics, have been successfully combined in the same hydrogels. Dynamic covalent bonds are mechanically stable yet still capable of exchanging, dissociating, or switching in response to external stimuli, empowering the hydrogels with self-healing properties, injectability and suitability for postprocessing and additive manufacturing. Here in this review, we first summarize the common dynamic covalent bonds used in hydrogel networks based on various chemical reaction mechanisms and the mechanical strength of these bonds at the single molecule level. Next, we discuss how dynamic covalent chemistry makes hydrogel materials more dynamic from the materials perspective. Furthermore, we highlight the challenges and future perspectives of dynamic covalent hydrogels.

Transformation of solid plastic waste to activated carbon fibres for wastewater treatment

In this study, the solid waste plastic was converted into activated carbon fibres through carbonization and chemical activation process. The morphological structure, composition, thermal stability and pore structure of the produced activated carbon materials were characterized. The results revealed that the activation process substantially increases the specific surface area of carbon materials via forming large micropores and mesopores (0.01-0.85 cm³g^-1) within average nano size range of 50-100 nm. This study provides an effective means to remove the thymol blue dye via adsorption over activated carbon (ACs) as adsorbent. Batch adsorption of thymol blue was conducted to verify the effect of variety of pH, dye concentrations, contact time, adsorbent dose and temperature. The highest dye removal efficiency (approximately 98.05%) of ACs generated from waste plastic polybags, cups and bottles was observed at 10 ppm of thymol blue dye. The results also exhibited that the dye adsorption was favourable at basic pH (9.0) and increasing amount of adsorbent dosage promotes the dye removal efficiency. The excellent dye removal performance was primarily due to the presence of higher available surface area on the surface of developed carbon fibres. In addition, the current results have given the large overview and useful information of dye removal properties by adsorption isotherm and kinetic measurements. The adsorption kinetics and thermodynamic prospective of formed ACs explored the physical, spontaneous and endothermic adsorption process. The as prepared ACs provided easy regeneration of adsorbents with fast response which further suggests the efficiency of nanoparticles to promote their usage up to 5 consecutive cycles. The current work illustrated that better means to transform solid waste plastic into carbon fibres for providing effective and cheap viable option for the fast removal of thymol blue dye from waste water samples.

Expansion Microscopy with a Thermally Adjustable Expansion Factor Using Thermoresponsive Biospecimen-Hydrogel Hybrids

Expansion microscopy (ExM) is a technique in which swellable hydrogel-embedded biological samples are physically expanded to effectively increase imaging resolution. Here, we develop thermoresponsive reversible ExM (T-RevExM), in which the expansion factor can be thermally adjusted in a reversible manner. In this method, samples are embedded in thermoresponsive hydrogels and partially digested to allow for reversible swelling of the sample-gel hybrid in a temperature-dependent manner. We first synthesized hydrogels exhibiting lower critical solution temperature (LCST)- and upper critical solution temperature (UCST)-phase transition properties with N-alkyl acrylamide or sulfobetaine monomers, respectively. We then formed covalent hybrids between the LCST or UCST hydrogel and biomolecules across the cultured cells and tissues. The resulting hybrid could be reversibly swelled or deswelled in a temperature-dependent manner, with LCST- and UCST-based hybrids negatively and positively responding to the increase in temperature (termed thermonegative RevExM and thermopositive RevExM, respectively). We further showed reliable imaging of both unexpanded and expanded cells and tissues and demonstrated minimal distortions from the original sample using conventional confocal microscopy. Thus, T-RevExM enables easy adjustment of the size of biological samples and therefore the effective magnification and resolution of the sample, simply by changing the sample temperature.

Robust superabsorbent p(MAPTAC) hydrogels with long physical cross-link junctions: synthesis, characterization and their performance for phosphate removal from wastewater

Ionic hydrogels with great water absorption capacity generally display poor mechanical strength that limits their use and narrows down their application areas. In this study, the new ionic hydrogel composed of poly (3-methacrylamido propyl trimethyl ammonium chloride) crosslinked with N, N-methylenebisacrylamide and sulphate ions was synthesized to obtain the hydrogel formulation which exhibits both huge swelling capacity and high mechanical stability, simultaneously. The successively synthesized gels with this strategy achieved a swelling capacity of 270 g/g and a modulus increased up to 20.43 kPa, indicating that they have a great potential to use in applications in which the both properties are required. The gels carrying a great number of cationic sites were also found to have a high affinity to phosphate ions, attaining an sorption value of 370 mg/g gel and to exhibit pseudo-second-order kinetic and Langmuir sorption isotherm models. The obtained results revealed that the new pMAPTAC gels have good potential for both phosphate sorption and high water uptake capacity without losing structural integrity owing to their enhanced mechanical strength.

Hydrogels Based Drug Delivery Synthesis, Characterization and Administration

Hydrogels represent 3D polymeric networks specially designed for various medical applications. Due to their porous structure, they are able to swollen and to entrap large amounts of therapeutic agents and other molecules. In addition, their biocompatibility and biodegradability properties, together with a controlled release profile, make hydrogels a potential drug delivery system. In vivo studies have demonstrated their effectiveness as curing platforms for various diseases and affections. In addition, the results of the clinical trials are very encouraging and promising for the use of hydrogels as future target therapy strategies.

pH/Thermo-Dual Responsive Tunable In Situ Cross-Linkable Depot Injectable Hydrogels Based on Poly(N-Isopropylacrylamide)/Carboxymethyl Chitosan with Potential of Controlled Localized and Systemic Drug Delivery

In the current study, cytocompatible in situ cross-linkable pH/thermo-dual responsive injectable hydrogels were prepared based on poly(N-isopropylacrylamide) and carboxymethyl chitosan, i.e., poly(CMCS-g-NIPAAm). The prepared formulations were aimed to be used as drug depot of 5-fluorouracil (5-FU) after subcutaneous administration in vivo. The phase transition from sol-gel state under physiologic temperature range was analyzed and confirmed by tube titling and optical transmittance measurements. The viscoelastic properties of gel formulations were confirmed by rheology determination via time sweep, temperature, and continuous ramp test. Oscillatory swelling cycles confirmed temperature effect and structural changes. pH and temperature sensitivity of dual responsive gels were analyzed at different pH and temperature programs. In vitro drug release profile displayed that developed formulations have the highest release in acidic pH at 25°C. The safety of blank gel formulations was evaluated against L929 cell lines via MTT assay and confirmed cytocompatibility with no detectable toxicity. In vitro cytotoxic potential of drug-loaded gels against HeLa and MCF-7 cancer cell lines confirmed that 5-FU has controlled cytotoxic potential in depot form in comparison to free 5-FU solution. The IC₅₀ values for free 5-FU (21 ± 05 μg/ml and 18 ± 66 μg/ml) were found higher in comparison to the loaded form. The copolymer structure formation was confirmed by NMR and FTIR spectroscopic analysis. TG and DSC analysis proved the thermal stability and phase transition temperatures of pure and copolymer samples, while SEM analysis showed the porous nature of in situ formed hydrogels. It was concluded from the results that the developed formulations have pH/temperature sensitivity with potential of systemic and intratumoral controlled drug delivery properties.

Investigation of the Formation Process of PNIPAM-Based Ionic Microgels

The formation process of poly(N-isopropylacrylamide) (PNIPAM)-based ionic microgels was investigated in this work. Different from the traditional formation process of covalent bond cross-linked PNIPAM-based microgels, a disassembling and reassembling process for PNIPAM-based ionic microgels was observed. During the formation process, loose microgels were first formed in a short time, and then, these loose microgels disassembled into smaller nanogel pieces. Meanwhile, the nanogel pieces reassembled into microgels by electrostatic interaction. After reassembling, large amounts of nanogels could be seen clearly in the interior of PNIPAM-based ionic microgels. The thermo-sensitivity and composition of the final prepared microgels were characterized by dynamic light scattering, infrared spectroscopy, and X-ray photoelectron spectroscopy.

A Near-Infrared and Temperature-Responsive Pesticide Release Platform through Core-Shell Polydopamine@PNIPAm Nanocomposites

Controlled stimuli-responsive release systems are a feasible and effective way to increase the efficiency of pesticides and help improve environmental pollution issues. However, near-infrared (NIR)-responsive systems for encapsulation of pesticides for controlling release have not been reported because of high cost and load ability of conventional NIR absorbers as well as complicated preparation process. Herein, we proposed polydopamine (PDA) microspheres as a photothermal agent owing to their abundant active sites, satisfactory photothermal efficiency, low cost, and easy fabrication, followed by capping with a PNIPAm thermosensitive polymer shell. In this core-shell PDA@PNIPAm hybrid system, the PDA core provided excellent temperature and NIR-light sensitivity as well as high loading capacity, while the PNIPAm applied as both a thermosensitive gatekeeper and a pesticide reservoir. The structure of the PDA@PNIPAm nanocomposites was characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, dynamic light scattering, and thermogravimetric analysis; the results showed that the nanocomposites had a well-defined core-shell configuration for efficient loading of small pesticide molecules. Moreover, the core-shell PDA@PNIPAm nanocomposites exhibited high loading capacity and temperature- or NIR-controlled release performance. Overall, this system has significant potential in controlled drug release and agriculture-related fields as a delivery system for pesticides with photothermal responsive behavior.