Cross-linking and modification of sodium alginate biopolymer for dye removal in aqueous solution

Synthesis of sodium alginate / polyvinyl alcohol / polyethylene glycol semi-interpenetrating hydrogel as a draw agent for forward osmosis desalination

Typically, hydrogels are described as three-dimensional networks of hydrophilic polymers that are able to capture a certain mass of water within their structure. Recently, hydrogels have been widely used as drawing agents in forward osmosis (FO) desalination processes. The major aim of this study is to prepare a novel semi-interpenetrating hydrogel by crosslinking sodium alginate (SA) and polyvinyl alcohol (PVA) by using the epichlorohydrin (ECH) crosslinker and polyethylene glycol (PEG) interpenetrated within the hydrogel's network as a linear polymer. Based on the optimum composition of SA/PVA composite hydrogel obtained from our earlier research, the effect of various percentages of PEG on the response of the hydrogel was investigated. The optimal composition of SA/PVA/PEG hydrogel was characterized by scanning electron microscopy (SEM), compression strength testing, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The morphological and mechanical properties of the SA/PVA/PEG semi-interpenetrating hydrogel were also compared to those of the SA/PVA composite hydrogel. Moreover, the performance of the optimal SA/PVA/PEG hydrogel in a FO batch unit as a drawing agent was investigated based on the optimal operation conditions from our previous experiments. The results showed that the optimal PEG/polymer blend mass ratio was 0.25, which increased the swelling ratio (SR) (%) of the hydrogel from 645.42 (of the neat SA/PVA hydrogel) to 2683. The SA/PVA/PEG semi-interpenetrating hydrogel was superior to the SA/PVA copolymer hydrogel in pore structure and mechanical properties. Additionally, in terms of FO desalination, the achieved water flux by SA/PVA/PEG hydrogel is higher than that accomplished by SA/PVA hydrogel.

Synthesis and characterization of an innovative sodium alginate/polyvinyl alcohol bioartificial hydrogel for forward-osmosis desalination

Recently, hydrogels have been widely applied as draw agents in forward osmosis (FO) desalination. This work aims to synthesize bioartificial hydrogel from a blend of sodium alginate (SA) and polyvinyl alcohol (PVA) using epichlorohydrin (ECH) as a crosslinker. Then this prepared hydrogel was applied as a draw agent with cellulose triacetate membrane in a batch (FO) cell. The effects of the PVA content in the polymer blend and the crosslinker dose on the hydrogel's swelling capacity were investigated to optimize the hydrogel's composition. Furthermore, the water flux and the reverse solute flux of the optimum SA/PVA hydrogel were evaluated in a batch (FO) unit under the effect of the hydrogel's particle size, feed solution (FS) temperature, FS concentration, and membrane orientation. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and compression strength tests were used to characterize the prepared hydrogel. Results revealed that the equilibrium swelling ratio (%) of 5228 was achieved with a hydrogel that had 25% PVA and a crosslinking ratio of 0.8. FO experiments revealed that the maximum water flux of 0.845 LMH achieved, when distilled water was used as FS, average hydrogel's particle size was 60 µm, and the FS temperature was 40 °C.

In-situ magnetic alginate coated chitosan core@shell beads with excellent performance in simulated and real wastewater treatment: Behavior, mechanisms, and new perspectives

Herein, a new hybrid magnetic core@shell biocomposite was prepared based on an alginate-bentonite core and a chitosan shell layer (mAB@Cs) where magnetic Fe3O4 NPs (50.7 nm) were in-situ generated on the surface via a simple non-thermal co-precipitation approach. The biocomposite has a high ability to magnetically separate and remove organic (ciprofloxacin (CPX)) and seven toxic inorganic (Cu2+, Cd2+, Co2+, Ni2+, Pb2+, Zn2+, and Hg2+) contaminants from simulated wastewater. Experimental results showed a CPX monolayer chemisorption with a Langmuir maximum adsorption capacity of 264.7 mg/g, maintained effectiveness up to the fifth cycle, and high removal rates of heavy metals ranging from 74.89 % to 99.86 % corresponding to adsorption capacities ranging from 12 to 20 mg/g. For a more accurate evaluation, the biocomposite was tested on a real urban wastewater sample (RWW) and it has manifested a noteworthy efficiency in removing a mixture of inorganic pollutants in terms of potassium K+ and orthophosphate phosphorous P-PO43-, and organic matter in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) with 46 %, 90 %, 84 %, and 64 % removal efficiencies, respectively. On top of this, a high inactivation rate of E. coli of the order of 96 % was recorded, making the prepared magnetic biocomposite adept for the simultaneous removal of emergent wastewater pollutants, from organic, inorganic, to pathogen microorganisms.

Engineering a self-healing grafted chitosan-sodium alginate based hydrogel with potential keratinocyte cell migration property and inhibitory effect against fluconazole resistance Candida albicans biofilm

Biofilms developed by microorganisms cause an extremely severe clinical problem that leads to drug failure. Bioactive polymeric hydrogels display potential for controlling the formation of microorganism-based biofilms, but their rapid biodegradability in these biofilm sites is still a major challenge. To overcome this, chitosan (CS), a natural functional biomaterial, has been used because of its effective penetrability in the cell wall of microorganisms; however, its fast biodegradability has restricted its further use. Hence, in this study, to improve the stability of CS and increase its penetration retention inside a biofilm, grafted CS was prepared and then crosslinked with sodium alginate (SA) to synthesize CS-poly(MA-co-AA)SA hydrogel via a free radical grafting method, therefore enhancing its antibiofilm efficiency against biofilms. The prepared hydrogel demonstrated excellent effectiveness against (≥90 % inhibition) biofilms of Candida albicans. Additionally, in vitro and in vivo safety assays established that the prepared hydrogel can be used in a biofilm microenvironment and might reduce drug resistance burden owing to its long-term antibiofilm effect and improved CS stability at the biofilm site. Furthermore, in vitro wound healing outcomes of hydrogel indicated its potential application for chronic wound treatment. This research opens a new advanced strategy for biofilm-associated infection treatment, including wound treatment.

Recent advances in cellulose- and alginate-based hydrogels for water and wastewater treatment: A review

From the environmental perspective, it is essential to develop cheap, eco-friendly, and highly efficient materials for water and wastewater treatment. In this regard, hydrogels and hydrogel-based composites have been widely employed to mitigate global water pollution as this methodology is simple and free from harmful by-products. Notably, alginate and cellulose, which are natural carbohydrate polymers, have gained great attention for their availability, price competitiveness, excellent biodegradability, biocompatibility, hydrophilicity, and superior physicochemical performance in water treatment. This review outlined the recent progress in developing and applying alginate- and cellulose-based hydrogels to remove various pollutants such as dyes, heavy metals, oils, pharmaceutical contaminants, and pesticides from wastewater streams. This review also highlighted the effects of various physical or chemical methods, such as crosslinking, grafting, the addition of fillers, nanoparticle incorporation, and polymer blending, on the physiochemical and adsorption properties of hydrogels. In addition, this review covered the alginate- and cellulose-based hydrogels' current limitations such as low mechanical performance and poor stability, while presenting strategies to improve the drawbacks of the hydrogels. Lastly, we discussed the prospects and future directions of alginate- and cellulose-based hydrogels. We hope this review provides valuable insights into the efficient preparations and applications of hydrogels.

Can an Alginate-based Wound Dressing Modified with Garden Cress Substitute for COE-PAK as a Wound Dressing? An In Vitro Study

AIM

The aim of the current study was to prepare a natural oral wound dressing from alginate modified with garden cress (GC), a rich source of antibacterial phytochemical compounds essential for wound healing.

MATERIALS AND METHODS

Sodium alginate (SA) dressing (negative control group), was prepared and modified with GC seeds extracts (25 µg/mL and 50 µg/mL) as the intervention groups, and COE-PAK was the positive control group. Cytotoxicity was measured using WST-1 assay (n = 15) after 24 and 48 hours. The in vitro wound healing assay (n = 15) was assessed in terms of wound width, and cell migration rate (0, 24, 48, and 72 hours). Agar diffusion test was performed to investigate the antibacterial action (n = 15) of the groups against Streptococcus mutans and Lactobacillus casei strains. Results were significant at p ≤ 0.05.

RESULTS

There was no statistically significant difference in cytotoxicity in all groups (p = 0.24 at 24 hours and 0.1 at 48 hours). Garden cress-containing groups revealed the lowest mean value of wound width (0.27 mm ± 0.01 and 0.23 mm ± 0.01 for 25 µg/mL and 50 µg/mL, respectively at 48 hours) and the highest mean value of cell migration rate (0.013 mm/hour ± 0.004 and 0.014 mm/hour ± 0.004 for 25 µg/mL and 50 µg/mL, respectively at 48 hours), in addition to the highest antibacterial action (1.49 mm ± 0.05 and 2.14 mm ± 0.09 for 25 µg/mL and 50 µg/mL, respectively against S. mutans, 1.43 mm ± 0.07 and 2.55 mm ± 0.09 for 25 µg/mL and 50 µg/mL, respectively against L. casei).

CONCLUSION

Alginate wound dressing modified with GC extract could be considered a promising wound dressing material in terms of wound healing and antibacterial action.

CLINICAL SIGNIFICANCE

Ready-to-use alginate-based wound dressing modified with GC extract may represent a promising natural alternative to the most commonly used oral wound dressing (COE-PAK).

Experimental Advances in the Real-Time Recording of Cross-Linking Alginate In Situ Gelation: A Review

Alginate-based hydrogels are promising smart materials widely employed in the food, bioengineering, and energy sectors. The development and optimization of their production require a thorough knowledge of gelation. In recent years, advanced experimental procedures have been developed for real-time cross-linking alginate reaction monitoring. Novel methods, such as customized rheometric setups, enable the recording of mechanical properties and morphological changes during hydrogel formation. These innovative techniques provide important insights into the gelation stages, the reaction rate, the diffusion of cross-linker to polymer chains, and the homogeneity of the gelling structures. Based on real-time experimental data, kinetic models are developed to enhance comprehension of the reaction mechanism and, eventually, to predict the gelation progress. The aim is to enable better control of the characterization of both the complex gelation and the propagated structures. This review aspires to present a comprehensive overview and evaluation of the breakthrough innovations of the real-time in situ recording of cross-linking alginate hydrogels and bead formation. A detailed analysis of the pioneering experimental developments provides a deep comprehension of the alginate gelation, including the parameters controlling the reaction.

Super-efficient removal and adsorption mechanism of anionic dyes from water by magnetic amino acid-functionalized diatomite/yttrium alginate hybrid beads as an eco-friendly composite

The development of eco-friendly, large-capacity and easy-to-separate adsorbent materials has always been the focus and difficulty of adsorption technology in wastewater treatment applications based on the characteristics of dye wastewater. Therefore, in this study, a green magnetic glycine(Gly)-functionalized diatomite(Dia)/yttrium alginate (Y-SA) hybrid bead composite (Dia-Gly-Y-SA@Fe₃O₄) was synthesized by the droplet polymerization, and characterized by various modern analytical techniques. The adsorption performance and adsorption mechanism of the composite were evaluated and elucidated by the removal of anionic dyes direct Blue 106 (DB 106), Congo red (CR) and direct red 13 (DR 13) from water. The results show that the composite is a macroparticle gelpolymer with an average particle size of about 1.5 mm, flower-like fold surface structure, abundant porosity and sensitive magnetic response, and displays ultrastrong adsorption ability for three dyes. The adsorption equilibrium of each dye can be reached quickly within 30 min, and the removal efficiency is more than 95% at pH 2.0 and decreases slightly with pH up to 9.0. The adsorption processes could be explained by the Pseudo-second-order rate equation well. All isotherm data fitted the Langmuir model well, and the maximum adsorption capacities were 1635, 2359 and 1165 mg/g for DB 106, CR and DR 13 at 298 K, respectively. The ultrastrong adsorption performance was due to the multisite interaction of physicochemical action and various hydrogen bonds between hybrid beads and dye anions. As a cost-effective magnetic macroparticle adsorbent prepared by natural ingredients, Dia-Gly-Y-SA@Fe₃O₄ composite exhibits much more stronger adsorption efficiency, better collectability and no secondary pollution than powder Dia, and would have a good application prospect for the purification of anionic dye wastewater with a wide pH range.

3D bioprinting of mineralizing cyanobacteria as novel approach for the fabrication of living building materials

Living building materials (LBM) are gaining interest in the field of sustainable alternative construction materials to reduce the significant impact of the construction industry on global CO2 emissions. This study investigated the process of three-dimensional bioprinting to create LBM incorporating the cyanobacterium Synechococcus sp. strain PCC 7002, which is capable of producing calcium carbonate (CaCO3) as a biocement. Rheology and printability of biomaterial inks based on alginate-methylcellulose hydrogels containing up to 50 wt% sea sand were examined. PCC 7002 was incorporated into the bioinks and cell viability and growth was characterized by fluorescence microscopy and chlorophyll extraction after the printing process. Biomineralization was induced in liquid culture and in the bioprinted LBM and observed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and through mechanical characterization. Cell viability in the bioprinted scaffolds was confirmed over 14 days of cultivation, demonstrating that the cells were able to withstand shear stress and pressure during the extrusion process and remain viable in the immobilized state. CaCO3 mineralization of PCC 7002 was observed in both liquid culture and bioprinted LBM. In comparison to cell-free scaffolds, LBM containing live cyanobacteria had a higher compressive strength. Therefore, bioprinted LBM containing photosynthetically active, mineralizing microorganisms could be proved to be beneficial for designing environmentally friendly construction materials.

Preparation of Hydrophobic Monolithic Supermacroporous Cryogel Particles for the Separation of Stabilized Oil-in-Water Emulsion

Here, we prepared hydrophobic cryogel particles with monolithic supermacropores based on poly-trimethylolpropane trimethacrylate (pTrim) by combining the inverse Leidenfrost effect and cryo-polymerization technique. The hydrophobic cryogel particles prepared by adopting this method demonstrated the separation of the stabilized O/W emulsion with surfactant. The prepared cryogel particles were characterized in terms of macroscopic shape and porous structure. It was found that the cryogel particles had a narrow size distribution and a monolithic supermacroporous structure. The hydrophobicity of the cryogel particles was confirmed by placing aqueous and organic droplets on the particles. Where the organic droplet was immediately adsorbed into the particles, the aqueous droplet remained on the surface of the particle due to repelling force. In addition, after it adsorbed the organic droplet the particle was observed, and the organic solvent was diffused into the entire particle. It was indicated that monolithic pores were distributed from the surface to the interior. Regarding the application of the hydrophobic cryogel particles, we demonstrated the separation of a stabilized oil-in-water emulsion, resulting in the successful removal of the organic solvent from the emulsion.

Preparation and Characteristics of Alginate Microparticles for Food, Pharmaceutical and Cosmetic Applications

Alginates are the most widely used natural polymers in the pharmaceutical, food and cosmetic industries. Usually, they are applied as a thickening, gel-forming and stabilizing agent. Moreover, the alginate-based formulations such as matrices, membranes, nanospheres or microcapsules are often used as delivery systems. Alginate microparticles (AMP) are biocompatible, biodegradable and nontoxic carriers, applied to encapsulate hydrophilic active substances, including probiotics. Here, we report the methods most frequently used for AMP production and encapsulation of different actives. The technological parameters important in the process of AMP preparation, such as alginate concentration, the type and concentration of other reagents (cross-linking agents, oils, emulsifiers and pH regulators), agitation speed or cross-linking time, are reviewed. Furthermore, the advantages and disadvantages of alginate microparticles as delivery systems are discussed, and an overview of the active ingredients enclosed in the alginate carriers are presented.

Environmentally Friendly Polyvinyl Alcohol-Alginate/Bentonite Semi-Interpenetrating Polymer Network Nanocomposite Hydrogel Beads as an Efficient Adsorbent for the Removal of Methylene Blue from Aqueous Solution

Hazardous chemicals like toxic organic dyes are very harmful to the environment and their removal is quite challenging. Therefore there is a necessity to develop techniques, which are environment friendly, cost-effective and easily available in nature for water purification and remediation. The present research work is focused on the development` and characterization of the ecofriendly semi-interpenetrating polymer network (semi-IPN) nanocomposite hydrogels composed of polyvinyl alcohol (PVA) and alginate (Alg) hydrogel beads incorporating natural bentonite (Bent) clay as a beneficial adsorbent for the removal of toxic methylene blue (MB) from aqueous solution. PVA-Alg/Bent nanocomposite hydrogel beads with different Bent content (0, 10, 20, and 30 wt%) were synthesized via external ionic gelation method. The designed porous and steady structure beads were characterized by the use of Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The performance of the beads as MB adsorbents was investigated by treating aqueous solutions in batch mode. The experimental results indicated that the incorporation of Bent (30 wt%) in the nanocomposite formulation sustained the porous structure, preserved water uptake, and increased MB removal efficiency by 230% compared to empty beads. Designed beads possessed higher affinity to MB at high pH 8, 30 °C, and fitted well to pseudo-second-order kinetic model with a high correlation coefficient. Moreover, the designed beads had good stability and reusability as they exhibited excellent removal efficiency (90%) after six consecutive adsorption-desorption cycles. The adsorption process was found be combination of both monolayer adsorption on homogeneous surface and multilayer adsorption on heterogeneous surface. The maximum adsorption capacity of the designed beads system as calculated by Langmuir isotherm was found to be 51.34 mg/g, which is in good agreement with the reported clay-related adsorbents. The designed semi-IPN PVA-Alg/Bent nanocomposite hydrogel beads demonstrated good adsorbent properties and could be potentially used for MB removal from polluted water.

Adsorption of methylene blue on sodium alginate-flax seed ash beads: Isotherm, kinetic and thermodynamic studies

In the present study, the adsorptive removal of methylene blue (MB) from wastewater was studied using the novel composite prepared by sodium alginate (SA) and flax seed ash (FS). The adsorption of MB was carried out using the composite beads consisting of different weight amounts of FS at different pH values and temperatures using different dye concentrations. The characterization studies of the composite beads were performed using Fourier-Transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and Brunauer-Emmett-Teller and Barrett-Joyner-Hallenda (BET-BJH) analyses. BET and BJH surface area values of SA-FS adsorbent beads were found to be 45.01 m²/g and 14.35 m²/g, respectively. During the studies, it was determined that the adsorption percentage of MB reached the maximum with 90% at pH = 7 and 50 °C. Furthermore, Langmuir model fits well for the adsorption of MB using SA-FS with different FS ratios, SA, and FS adsorbents. The maximum adsorption capacity obtained from Langmuir model was found to be 333.3 mg/g for SA-FS-2 composite beads at pH = 7 and 50 °C. The adsorption kinetics were interpreted well by pseudo-second order model for SA, FS and SA-FS adsorbents. The calculated thermodynamic parameters indicated that MB adsorption by FS, SA, and SA-FS were spontaneous and an endothermic.