Preparation and characterization of pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Stimulus-Responsive Hydrogels for Targeted Cancer Therapy

Cancer is a highly heterogeneous disease and remains a global health challenge affecting millions of human lives worldwide. Despite advancements in conventional treatments like surgery, chemotherapy, and immunotherapy, the rise of multidrug resistance, tumor recurrence, and their severe side effects and the complex nature of the tumor microenvironment (TME) necessitates innovative therapeutic approaches. Recently, stimulus-responsive nanomedicines designed to target TME characteristics (e.g., pH alterations, redox conditions, enzyme secretion) have gained attention for their potential to enhance anticancer efficacy while minimizing the adverse effects of chemotherapeutics/bioactive compounds. Among the various nanocarriers, hydrogels are intriguing due to their high-water content, adjustable mechanical characteristics, and responsiveness to external and internal stimuli, making them promising candidates for cancer therapy. These properties make hydrogels an ideal nanocarrier for controlled drug release within the TME. This review comprehensively surveys the latest advancements in the area of stimulus-responsive hydrogels for cancer therapy, exploring various stimuli-responsive mechanisms, including biological (e.g., pH, redox), chemical (e.g., enzymes, glucose), and physical (e.g., temperature, light), as well as dual- or multi-stimuli responsiveness. Furthermore, this review addresses the current developments and challenges in hydrogels in cancer treatment. Our aim is to provide readers with a comprehensive understanding of stimulus-responsive hydrogels for cancer treatment, offering novel perspectives on their development for cancer therapy and other medical applications.

Formulation and In Vitro Assessment of Polymeric pH-Responsive Nanogels of Chitosan for Sustained Delivery of Madecassoside

Madecassoside, a triterpenoid saponin compound mainly isolated from the gotu kola herb (Centella asiatica), shows an extensive range of biological activities, including antiapoptotic, antioxidant, anti-inflammatory, moisturizing, neuroprotective, and wound healing effects. It has been highly used in the management of eczema, skin wounds, and other diseases. Due to poor oral bioavailability, membrane permeability, and intestinal absorption, the clinical application of the madecassoside is limited. Hence, a drug carrier system is needed that not only sustains the release of the madecassoside but also overcomes the drawbacks associated with its administration. Therefore, the authors prepared novel pH-responsive chitosan-based nanogels for the sustained release of madecassoside. Free radical polymerization technique was used for cross-linking of polymer chitosan and monomer methacrylic acid in the presence of cross-linker N',N'-methylene bis(acrylamide). The decrease in polymer crystallinity after polymerization and development of nanogels was demonstrated by XRD and FTIR analysis. The effects of nanogel contents on polymer volume, sol-gel analysis, swelling, drug loading, and release were investigated. Results indicated that high swelling and maximum release of the drug occurred at pH 7.4 compared to pH 1.2 and 4.6, indicating the excellent pH-sensitive nature of the engineered nanogels. High swelling and drug release were perceived with the integration of a high quantity of chitosan, while a decline was observed with the high integration of N',N'-methylene bis(acrylamide) and methacrylic acid contents. The same effects of nanogel contents were shown for drug loading too. Sol fraction was reduced, while gel fraction was enhanced by increasing the chitosan load, N',N'-methylene bis(acrylamide), and methacrylic acid. The Korsmeyer-Peppas model of kinetics was trailed by all nanogel formulations with non-Fickian diffusion. The results demonstrated that prepared nanogels can be employed for sustained release of the madecassoside.

Anticorrosive properties of chitosan-derivatives coatings on Mg AZ31 alloy in Hank's Balanced Salt Solution

This study describes the preparation of chitosan-derivatives coatings on AZ31 Mg alloy for corrosion protection in Hank's Balanced Salt Solution (HBSS). The derivatives were prepared by reacting chitosan with natural aldehydes (vanillin, benzaldehyde and cinnamaldehyde) and the coatings were characterized by means of water contact angle, scanning electron microscopy and swelling essays. The corrosion behavior of the samples was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution essays. All derivatives present superior corrosion protection than neat chitosan and the best performance is observed for the vanillin derivative with the highest modification degree, which present hydrogen evolution rate of 0.05 mL cm-2 day-1, below the tolerance limit for biomedical application, and |Z|max in the order of 104.6 Ω cm2 even after 14 days of exposure to the corrosive solution.

Chitosan-based intelligent polymeric networks for site-specific colon medication delivery: A comprehensive study on controlled release of diloxanide furoate and network formation dynamics

Oral medications are prone to gastric degradation and enzymatic inactivation, diminishing their efficacy. This study investigates a solution by developing intelligent polymeric networks, incorporating chitosan, methacrylic acid, N, N, methylene bisacrylamide, and montmorillonite clay, to enable the controlled release of Diloxanide Furoate (DF), an anti-protozoal drug. Employing a swelling-assisted diffusion technique, drug loading percentages varied from 63.96 % to 76.82 % among different formulations. Increased chitosan and methacrylic acid content enhanced drug loading, while N, N, methylene bisacrylamide and montmorillonite clay demonstrated an inverse relationship affecting diffusion and swelling. Equilibrium swelling studies unveiled formulation-dependent behaviors, with chitosan reducing swelling and methacrylic acid promoting it. Higher N, N, methylene bisacrylamide concentrations decreased swelling, indicating a denser cross-linked structure, while montmorillonite clay reduced hydrophilicity and swelling capacity. Further analyses confirmed successful gel formation, particularly in formulations with higher chitosan, methacrylic acid, and N, N, methylene bisacrylamide content, while montmorillonite clay limited gel fraction due to restricted polymer chain mobility. Techniques such as Fourier transform infrared spectroscopy, Differential scanning calorimetry, and thermal gravimetric analyses supported network development, enhancing thermal stability and cross-linking density. This research underscores the flexibility of polymeric networks for precise drug delivery, offering potential advancements in targeted therapies for various medical conditions.

Vanillin loaded-physically crosslinked PVA/chitosan/itaconic membranes for topical wound healing applications

Vanillin loaded-physically crosslinked hydrogel membranes made of PVA/chitosan/itaconic acid (PVA-CS-IA) were prepared using freezing-thawing (F-T) cycle method. To ensure the entanglement of PVA-CS-IA chains, three F-T cycles were repeated. The polymeric chains entanglements were confirmed and characterized by different instrumental characterizations. Physicochemical properties for example, swelling ratio, mechanical characteristics, gel fraction percentage (GF%), hydrolytic degradation, and thermal stability of PVA-CS-IA membrane were discussed in detail. The findings showed that the swelling ratio, mechanical characteristics, and hydrolytic degradation of the crosslinked membranes enhanced with increasing CS-IA contents in membranes composition; however, GF% gradually declined with CS-IA content. Additionally, cell viability test using HFB-4 cell line and antimicrobial activity against Staphylococcus aureus and Escherichia coli were evaluated using MTT assay and the bacterium growth inhibition percentage method; respectively. Notably, with varying incubation durations and membrane concentrations, all examined constructed hydrogels showed significant cell survival percentages. The findings supported the notion that produced hydrogel membranes might be used in a professional setting as antibacterial dressings or biomaterials for quick wound healing rate.

Impact of the Configurational Microstructure of Carboxylate-Rich Chitosan Beads on Its Adsorptive Removal of Diclofenac Potassium from Contaminated Water

A novel adsorbent-contaminant system was investigated for its ability to remove a contaminant of emerging concern, diclofenac potassium, from contaminated water. Bio-based crosslinked chitosan beads functionalized with poly(itaconic acid) side chains were examined for their potential to remove the emerging contaminant. To evaluate the impact of the polymeric microstructure on its adsorptive capacity, several adsorbent samples were prepared using different combinations of initiator and monomeric concentrations. Fourier Transform Infrared (FTIR) analysis confirmed the crosslinking of the chitosan chains and the incorporation of the carboxylic groups on the surface of the final chitosan beads. After the grafting copolymerization process, an additional peak at 1726 cm-1 corresponding to the carboxylic C=O groups of the grafted chains appeared, indicating the successful preparation of poly(IA)-g-chitosan. Thermal stability studies showed that the grafting copolymerization improved the thermal stability of the beads. X-ray and Scanning Electron Microscopy confirmed the successful grafting of the itaconic acid on the surface of the beads. The study revealed that the higher the initiator concentration, the greater the number of side chains, whereas the higher the monomeric concentration, the longer the length of these side chains. The adsorption mechanism involved hydrogen bonding to the carboxylic groups of the grafted chains along with n-π* stacking interaction between the amino group of the chitosan and the aromatic rings of diclofenac potassium. The adsorption efficiencies of diclofenac potassium onto the grafted beads were significantly improved compared to the unfunctionalized chitosan beads, reaching values above 90%. The removal efficiency of grafted chitosan increased with an increase in the concentration in the range of 10-30 ppm and then flattened out in the range of 30-50 ppm. The removal efficiencies of 1-50 ppm of DCF ranged between about 75% and 92% for the grafted chitosan and 30-45% for the crosslinked chitosan. Rapid adsorption occurred within 20 min for all grafted sample combinations, and the adsorption kinetics followed a pseudo-second-order model with qe values ranging from 28 to 44.25 g/mg and R2 values greater than 0.9915. The results highlight the potential of grafted chitosan beads in removing emerging contaminants from contaminated water without harming the environment.

A review on heavy metal biosorption utilizing modified chitosan

Heavy metal pollution in water bodies is a global concern. The prominent source of metal contamination in aqueous streams and groundwater is wastewater containing heavy metal ions. Elevated concentrations of heavy metals in water bodies can have a negative impact on water quality and public health. The most effective way to remove metal contaminants from drinking water is thought to be adsorption. A deacetylated derivative of chitin, chitosan, has a wide range of commercial uses since it is biocompatible, nontoxic, and biodegradable. Due to its exceptional adsorption behavior toward numerous hazardous heavy metals from aqueous solutions, chitosan and its modifications have drawn a lot of interest in recent years. Due to its remarkable adsorption behavior toward a range of dangerous heavy metals, chitosan is a possible agent for eliminating metals from aqueous solutions. The review has focused on the ideas of biosorption, its kinds, architectures, and characteristics, as well as using modified (physically and chemically modified) chitosan, blends, and composites to remove heavy metals from water. The main objective of the review is to describe the most important aspects of chitosan-based adsorbents that might be beneficial for enhancing the adsorption capabilities of modified chitosan and promoting the usage of this material in the removal of heavy metal pollutants.

Poly Ethylene Glycol (PEG)-Based Hydrogels for Drug Delivery in Cancer Therapy: A Comprehensive Review

Hydrogel-based drug delivery systems (DDSs) can leverage therapeutically beneficial outcomes in cancer therapy. In this domain, polyethylene glycol (PEG) has become increasingly popular as a biomedical polymer and has found clinical use. Owing to their excellent biocompatibility, facile modifiability, and high drug encapsulation rate, PEG hydrogels have shown great promise as drug delivery platforms. Here, the progress in emerging novel designs of PEG-hydrogels as DDSs for anti-cancer therapy is reviewed and discussed, focusing on underpinning multiscale release mechanisms categorized under stimuli-responsive and non-responsive drug release. The responsive drug delivery approaches are discussed, and the underpinning release mechanisms are elucidated, covering the systems functioning based on either exogenous stimuli-response, such as photo- and magnetic-sensitive PEG hydrogels, or endogenous stimuli-response, such as enzyme-, pH-, reduction-, and temperature-sensitive PEG hydrogels. Special attention is paid to the commercial potential of PEG-based hydrogels in cancer therapy, highlighting the limitations that need to be addressed in future research for their clinical translation.

Development and Evaluation of Sodium Alginate/Carbopol 934P-Co-Poly (Methacrylate) Hydrogels for Localized Drug Delivery

This research was carried out to create a pH-responsive polymeric system for the targeted drug delivery of Diloxanide furoate. It relied on sodium alginate (Na-Alg) and Carbopol 934P as building blocks. Using an aqueous free radical polymerization method, SCH1-SCH12 was created with varying polymer, MAA, and MBA input ratios. Positive outcomes were seen in the swelling and release profiles at higher pH levels. Hydrogel formation, as well as component compatibility, thermal stability, and Diloxanide furoate loading, were all validated by instrumental characterization. A drug loading percentage of 83.56% was determined, with the swelling reaching 743.19%. For the formulation with MBA, the gel fraction was 94.58%. The release of diloxanide furoate increased to 91.77% at neutral pH. The formulation containing Carbopol 934P provided the highest mucoadhesion force (3993.42 dynes/cm²). The created hydrogel has been shown to be biocompatible by toxicological testing of the network. Based on the findings, the created polymeric nexus proved promising for pH-dependent localized and regulated delivery of Diloxanide furoate.

In-vitro and in-vivo evaluation of biocompatible polymeric microgels for pH- driven delivery of Ketorolac tromethamine

The aim of the current study was to prepare glutamic acid crosslinked poly(itaconic acid/methacrylic acid) microgels for pH-responsive delivery of ketorolac tromethamine, using aqueous free radical polymerization technique. The polymerization of polymer with monomers was carried out by a crosslinking agent N', N'-methylene bisacrylamide in the presence of initiator ammonium persulfate. The prepared microgels were characterized for structure, surface morphology, thermal stability, and crystallinity. Similarly, studies such as sol-gel analysis, drug loading, and polymer volume fraction were performed for the fabricated microgels. The pH-sensitivity of the developed microgels was investigated at three different pH values i.e., pH 1.2, 4.6, and 7.4 by swelling and in-vitro drug release studies. Maximum swelling and drug release were found at pH 7.4 as compared to pH 1.2 and 4.6, which indicated the pH-sensitive nature of the prepared microgels. The toxicity of the prepared microgels was evaluated by cell line and HET-CAM test, which demonstrated no toxic effect of the prepared microgels. In-vivo study was carried out on rabbits and high plasma concentration was reported for the drug loaded microgels as compared to drug solution and commercial product Keten. Hence, the prepared microgel system could be employed as an excellent carrier for the controlled drug delivery system.

pH Sensitive Pluronic Acid/Agarose-Hydrogels as Controlled Drug Delivery Carriers: Design, Characterization and Toxicity Evaluation

The objective of this study was to fabricate and evaluate a pH sensitive cross-linked polymeric network through the free radical polymerization technique for the model drug, cyclophosphamide, used in the treatment of non-Hodgkin's lymphoma. The Hydrogels were prepared using a polymeric blend of agarose, Pluronic acid, glutaraldehyde, and methacrylic acid. The prepared hydrogels were characterized for drug loading (%), swelling pattern, release behavior, the ingredient's compatibility, structural evaluation, thermal integrity, and toxicity evaluation in rabbits. The new polymer formation was evident from FTIR findings. The percentage loaded into the hydrogels was in the range of 58.65-75.32%. The developed hydrogels showed significant differences in swelling dynamics and drug release behavior in simulated intestinal fluid (SIF) when compared with simulated gastric fluid (SGF). The drug release was persistent and performed in a controlled manner for up to 24 h. A toxicity study was conducted on white albino rabbits. The developed hydrogels did not show any signs of ocular, skin, or oral toxicity; therefore, these hydrogels can be regarded as safe and potential carriers for controlled drug delivery in biomedical applications.

Optimization, in vitro release and toxicity evaluation of novel pH sensitive itaconic acid-g-poly(acrylamide)/sterculia gum semi-interpenetrating networks

BACKGROUND

In recent era, pH sensitive polymeric carriers that combines the materials engineering and medicine is gaining researcher's attention as they maximizes drug concentration at site of absorption and reduces side effects for e.g. orally administered cetirizine HCl (CTZ HCl) upsets the stomach and furthermore shows high intestinal absorption. Thus, development of pH sensitive hydrogels with sufficient mechanical strength will be good candidate to address this issue.

METHODS

Here, we developed pH sensitive itaconic acid-g-poly(acrylamide)/sterculia gum (IA-g-poly(AM)/sterculia gum) semi-interpenetrating network (semi-IPN) by free radical polymerization technique for intestinal delivery of CTZ HCL.

RESULTS

Optimized formulation (I5) with 6% w/w IA showed negligible swelling at pH 1.2, and maximum swelling at pH 7.4. Solid state characterization of optimized formulation showed successful development of semi-IPN structure and incorporation of drug without any noticeable drug-carrier interaction. In vitro release study showed biphasic pH dependent release of CTZ HCl, where initial burst release was observed at acidic pH followed by sustained release at basic pH. Acute oral toxicity and histopathological studies confirmed the non-toxic nature of IA-g-poly(AM)/sterculia gum.

CONCLUSION

Conclusively, developed biocompatible semi-IPN hydrogels with sufficient pH sensitivity and mechanical strength could serve as a potential carrier for intestinal delivery of CTZ HCL to maximize its absorption and reduce side effects.

Aqueous Modification of Chitosan with Itaconic Acid to Produce Strong Oxygen Barrier Film

In this study, the chemical modification of chitosan using itaconic acid as a natural-based unsaturated dicarboxylic acid was investigated. In an aqueous environment, the amine group of chitosan reacts with itaconic acid to produce a chitosan derivative with pyrrolidone-4-carboxylic acid group. On the basis of the elemental analysis, 15% of the amine groups of chitosan reacted, thus creating modified chitosan with amine and carboxylic acid functionalities. Due to the presence of amine and carboxylic acid groups, the surface charge properties of the chitosan were notably altered after itaconic acid modification. In an aqueous solution, the modified chitosan exhibited zwitterionic properties, being cationic at low pH and turning anionic when the pH was increased over 6.5, whereas the original chitosan remained cationic until pH 9. Furthermore, it was demostrated that the modified chitosan was suitable for the preparation of a self-standing film with similarly high transparency but notably higher mechanical strength and oxygen barrier properties compared to a film made from the original chitosan. In addition, the thermal stability of the modified chitosan film was higher than that of the original chitosan film, and the modified chitosan exhibited flame-retardant properties.

Fundamental Concepts of Hydrogels: Synthesis, Properties, and Their Applications

In the present review, we focused on the fundamental concepts of hydrogels-classification, the polymers involved, synthesis methods, types of hydrogels, properties, and applications of the hydrogel. Hydrogels can be synthesized from natural polymers, synthetic polymers, polymerizable synthetic monomers, and a combination of natural and synthetic polymers. Synthesis of hydrogels involves physical, chemical, and hybrid bonding. The bonding is formed via different routes, such as solution casting, solution mixing, bulk polymerization, free radical mechanism, radiation method, and interpenetrating network formation. The synthesized hydrogels have significant properties, such as mechanical strength, biocompatibility, biodegradability, swellability, and stimuli sensitivity. These properties are substantial for electrochemical and biomedical applications. Furthermore, this review emphasizes flexible and self-healable hydrogels as electrolytes for energy storage and energy conversion applications. Insufficient adhesiveness (less interfacial interaction) between electrodes and electrolytes and mechanical strength pose serious challenges, such as delamination of the supercapacitors, batteries, and solar cells. Owing to smart and aqueous hydrogels, robust mechanical strength, adhesiveness, stretchability, strain sensitivity, and self-healability are the critical factors that can identify the reliability and robustness of the energy storage and conversion devices. These devices are highly efficient and convenient for smart, light-weight, foldable electronics and modern pollution-free transportation in the current decade.

Development and evaluation of stimulus-sensitive microgels for controlled drug delivery

The novelty of the present work was focused on the synthesis of pH- and temperature-responsive cross-linked poly(methacrylic acid-co-acrylamide) (p(MAA-co-AM)) microgels for controlled drug delivery. A series of cross-linked microgels was successfully prepared by inverse-suspension polymerization using N,N′-methylenebisacrylamide as a cross-linking agent and potassium persulfate as an initiator. The swelling of the microgels was investigated as a function of pH (2.1 and 7.4) and temperature (20–50°C). The prepared microgels were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy (SEM), particle size analysis and drug-release behavior analysis. FTIR and thermal studies confirmed the formation of a new cross-linked p(MAA-co-AM) polymer. SEM revealed that the microgels were made of spherical, slightly rough and cross-linked particles. To study the controlled-drug-release behavior of microgels, captopril was successfully loaded as a model drug by using an in situ method. The maximum in vitro drug release was up to 96 and 55% at pH 7.4 and 2.1, respectively. All formulations showed pH-dependent drug release following the Higuchi model of drug-release mechanism. In light of the results obtained from the study, it was concluded that p(MAA-co-AM) microgels have potential applications in release of drugs in a controlled manner with respect to pH and temperature.

Fabrication and characterization of a novel semi-interpenetrating network hydrogel based on sodium carboxymethyl cellulose and poly(methacrylic acid) for oral insulin delivery

In this research, pH-sensitive semi-interpenetrating polymer network hydrogels based on sodium carboxymethyl cellulose and poly(methacrylic acid) were synthesized using free radical polymerization and semi-interpenetrating polymer network approach for oral administration of insulin. The chemical structure and thermal stability of the hydrogels were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis measurements. The interior morphology was observed by scanning electron microscopy and the inner structure exhibited a porous honeycomb-like shape. The investigations on the swelling properties of hydrogels revealed their ability to response to pH value change. The in vitro release behavior of insulin was pH dependent and the release of insulin was much lower at pH 1.2 compared to pH 6.8. In vitro cytotoxicity assay indicated that the hydrogels were noncytotoxic to HeLa cells. A sustained reduction in blood glucose level was observed after oral administration of insulin-loaded hydrogel to diabetic rats at 75 IU/kg. These results indicated that the hydrogel would be a promising vehicle for oral insulin delivery systems.

Chitosan Grafted Adsorbents for Diclofenac Pharmaceutical Compound Removal from Single-Component Aqueous Solutions and Mixtures

The main purpose of this study was to investigate the synthesis of some cross-linked carboxyl-grafted chitosan derivatives to be used as selective adsorbents for diclofenac (DCF) pharmaceutical compounds from aqueous mixtures. Four different materials were synthesized using succinic anhydride (CsSUC), maleic anhydride (CsMAL), itaconic acid (CsITA), and trans-aconitic acid (CsTACON) as grafting agents. After synthesis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were performed before and after DCF adsorption. In addition, a complete adsorption evaluation was carried out for all materials studying some important parameters. The optimum pH was 4; the amino groups of DCF can be protonated at pH = 4 (–NH⁺), so this groups can easily attract the clear negatively carboxyl moieties (–COO⁻) of the chitosan adsorbents. The Q_m for CsTACON was higher than those of the other materials, at all temperatures studied. By altering the temperature from 25 to 35 °C, an increase (16%) of Q_m (from 84.56 to 98.34 mg g⁻¹) was noted, while similar behavior was revealed after a further increase of temperature from 35 to 45 °C, improving by 5% (from 98.34 to 102.75 mg g⁻¹). All isotherms were fitted to Langmuir, Freundlich, and Langmuir-Freundlich (L-F) models). In addition, a kinetic model was proposed taking into account not only the interactions but also the diffusivity of the molecule (DCF) into the polymeric network. The behavior of the prepared chitosan materials in simultaneously removing other compounds (synergetic or antagonistic) was also evaluated by experiments performed in mixtures. DCF presented the highest removal from the mixture in the order: CsTACON (92.8%) > CsITA (89.5%) > CsSUC (80.9%) > CsMAL (66.2%) compared to other pharmaceutical compounds (salicylic acid, ibuprofen and ketoprofen). Desorption was achieved by using different eluants (either water or organic). The highest desorption ability was found for acetone (100% for CsTACON, CsSUC, CsMAL and 77% for CsITA) for all materials.

Stimuli-responsive bio-based polymeric systems and their applications

This article highlights the properties of stimuli-responsive bio-based polymeric systems and their main intelligent applications.

A statistical approach of zinc remediation using acidophilic bacterium via an integrated approach of bioleaching enhanced electrokinetic remediation (BEER) technology

The aim of the present study was to isolate an indigenous acidophilic bacterium from tannery effluent contaminated sludge (TECS) sample and evaluate its potentiality towards the removal of zinc using an integrated approach of bioleaching enhanced electrokinetic remediation (BEER) technology in zinc spiked soil at an initial concentration of 1000 mg/kg. The isolated acidophilic bacterium was characterized by biochemical and 16S rRNA molecular identification and was named as Serratia marcescens SMAR1 bearing an accession no. MG742410 in NCBI database. The effect of pH and inoculum dosage of SMAR 1 strain showed an optimal growth at pH 5.0 and 4% (v/v) respectively. Based on these experimental data, a statistical analysis was done using Design Expert computer software, v11 to study the interaction between the process parameters with respect to zinc reduction as an output response. Electrokinetic experiments were conducted in a customised EK cell under optimised process conditions, employing titanium electrodes. Experiments for zinc removal were demonstrated for bioleaching, electrokinetic (EK) and BEER technology. On comparing, the integrated process was found to evidence as an excellent metal remediation option with a maximum zinc removal of 93.08% in 72 h than plain bioleaching (72.86%) and EK (56.67%) in 96 h. This is the first report of zinc removal in a short period of time using Serratia marcescens. It is therefore concluded that the BEER approach can be regarded as an effective technology in cleaning up the metal contaminated environment with an easy recovery and reuse option within short period of time.

A review on acrylic based hydrogels and their applications in wastewater treatment

The acrylic based hydrogels have attracted the attention of many researchers in the field of pollutants adsorption such as dyes and metal cations due to their high swelling and adsorption capacities. This review introduces acrylic based hydrogels and focuses on their adsorption properties. We first described the methods for synthesizing hydrogels. Usual methods of characterization of acrylic based hydrogels such as swelling, adsorption capacity and desorption efficiency of the pollutants have been investigated. In addition, the adsorption isotherm and kinetic models which determine the mechanism of pollutants' adsorption by hydrogels have been introduced and relations that determine the values of thermodynamic parameters which define accomplishment of adsorption process have been investigated. In the following sections, a perfect insight has been provided on natural and synthetic acrylic based hydrogels. The effective parameters of swelling and adsorption by acrylic based hydrogels have been reviewed and the mechanism of pollutant's adsorption by acrylic based hydrogels has been discussed.

Effect of vinyl montmorillonite on the physical, responsive and antimicrobial properties of the optimized polyacrylic acid/chitosan superabsorbent via Box-Behnken model

This work aims to study the effect of a vinyl-modified montmorillonite (VMT) on the physical and antimicrobial properties of chitosan-graft-polyacrylic acid superabsorbent (Ch-g-PA). Ch-g-PA was first optimized using Box-Behnken design to obtain the maximum equilibrium swelling, and the model was efficient to express the experimental swelling data (R² = 0.999). VMT was further added to the optimized Ch-g-PA in different contents 0, 4, 7 and 10 wt%. FTIR confirmed the successful synthesis of the copolymers and their nanocomposites. Morphology and the average pores size were studied using SEM. Wide angle X-ray diffraction showed the formation of exfoliated nanocomposites after VMT addition. Thermal stability studied by TGA was greatly enhanced in the presence of VMT. The swelling kinetics by Voigt-based viscoelastic model showed that the equilibrium swelling was increased by increasing the VMT up to 7 wt% then decreased after further incorporation. The superabsorbents exhibited salt and pH-responsive properties and showed a pH-reversibility at two buffer solutions (pH = 2 and pH = 9). Moreover, the prepared superabsorbents exhibited a strong bacterial and fungal killing ability which becomes more pronounced upon increasing the VMT content. The obtained results encourage the usage of the prepared copolymer nanocomposites in many fields as antimicrobial superabsorbents of improved physical properties.

Effect of an alkaline environment on the engineering behavior of cement-stabilized/solidified Zn-contaminated soils

Although the stabilization/solidification method has been widely used for remediation of heavy metal-contaminated soils in recent decades, the engineering behavior and mobility of heavy metal ions under alkaline groundwater conditions are still unclear. Therefore, the unconfined compressive strength test (UCS) combined with toxicity characteristic leaching procedure (TCLP) and general acid neutralization capacity (GANC) was used to investigate the effects of alkalinity (using NaOH to simulate alkalinity in the environment) on the mechanical and leaching characteristics of cement-solidified/stabilized (S/S) Zn-contaminated soils. Moreover, the microstructure was analyzed using the scanning electron microscope (SEM) technology. The results indicated that alkaline environment could accelerate the UCS development compared with specimens without soaking in NaOH solution,, regardless of whether the specimens contained Zn²⁺ or not. And the UCS varied obviously attributed to the variations of both NaOH concentration and soaking time. Except for the specimens soaked for 90 days, the leached Zn²⁺ concentrations were higher than that of without soaking. However, the leachability of Zn²⁺ in all the stabilized specimens is in the regulatory level. ANC results indicated that the Zn²⁺ leaching behavior can be divided into three stages related to the initial leachate pH. Moreover, SEM results proved that the alkaline environment could actually facilitate the cement hydration process. The results proved in the present paper could be useful in treating the heavy metal-contaminated soils involved in the solidification/stabilization technology under alkaline environment.

The Mechanical Properties of a Poly(methyl methacrylate) Denture Base Material Modified with Dimethyl Itaconate and Di-n-butyl Itaconate

This study investigates a wide range of clinically relevant mechanical properties of poly(methyl methacrylate) (PMMA) denture base materials modified with di-methyl itaconate (DMI) and di-n-butyl itaconate (DBI) in order to compare them to a commercial PMMA denture base material. The commercial denture base formulation was modified with DMI and DBI by replacing up to 10 wt% of methyl methacrylate (MMA) monomer. The specimens were prepared by standard bath curing process. The influence of the itaconate content on hardness, impact strength, tensile, and thermal and dynamic mechanical properties was investigated. It is found that the addition of di-n-alkyl itaconates gives homogenous blends that show decreased glass transition temperature, as well as decrease in storage modulus, ultimate tensile strength, and impact fracture resistance with increase in the itaconate content. The mean values of surface hardness show no significant change with the addition of itaconates. The magnitude of the measured values indicates that the poly(methyl methacrylate) (PMMA) denture base material modified with itaconates could be developed into a less toxic, more environmentally and patient friendly product than commercial pure PMMA denture base material.