Poly (Vinyl Alcohol) Hydrogels Boosted with Cross-Linked Chitosan and Silver Nanoparticles for Efficient Adsorption of Congo Red and Crystal Violet Dyes.

In our previous work, three different weight ratios of chitosan/PVA (1:3, 1:1, and 3:1) were blended and then cross-linked with trimellitic anhydride isothiocyanate (TAI) at a concentration depending on their chitosan content, obtaining three hydrogels symbolized by H13, H11, and H31. Pure chitosan was cross-linked with TAI, producing a hydrogel symbolized by H10. Further, three H31-based silver nanoparticles composites (H31/AgNPs1%, H31/AgNPs3%, and H31/AgNPs5%) were also synthesized. They were investigated, for the first time in this study, as adsorbents for Congo Red (CR) and Crystal Violet (CV) dyes. The removal efficiency of CR dye increased with increasing H10 content in the hydrogels, and with increasing AgNP content in the composites, reaching 99.91% for H31/AgNPs5%. For CV dye, the removal efficiency increased with the increase in the PVA content. Furthermore, the removal efficiency of CV dye increased with an increasing AgNP content, reaching 94.7% for H31/AgNPs5%. The adsorption capacity increased with the increase in both the initial dye concentration and temperature, while with an increasing pH it increased in the case of CV dye and decreased in the case of CR dye. The adsorption of CV dye demonstrated that the Freundlich isotherm model is better suited for the experimental results. Moreover, the results were best fitted with pseudo-second-order kinetic model.

Evaluation of the in vitro anti-inflammatory and anti-Helicobacter pylori activities of chitosan-based biomaterials modified with copper oxide nanoparticles.

For chemical modification, p-aminobenzoic acid was incorporated into chitosan Schiff base (ACsSB) and chitosan (ACs). Two ACs-based CuO nanoparticles composites; ACs/CuONPs-1 % and ACs/CuONPs-5 %, were also synthesized. Their structures were emphasized utilizing several analytical techniques; elemental analysis, FTIR, 1H NMR, XRD, SEM, EDX and TEM. Compared with standard cyclooxygenase (COX) inhibitor, Celecoxib, the prepared biomaterials showed in vitro selective inhibitory effectiveness against COX-2 enzyme that could be sorted, according to their MIC values that produce 50 % inhibition of COX-2 enzyme activity, as follows: Celecoxib (0.28 µg/mL) > ACs/CuONPs-5 % (4.1 µg/mL) > ACs/CuONPs-1 % (14.8 µg/mL) > ACs (38.5 µg/mL) > ACsSB (58.9 µg/mL) > chitosan (>125 µg/mL). Further, ACs/CuONPs-5 % has more in vitro inhibition efficiency towards Helicobacter pylori (H. pylori) than the other prepared biomaterials. Interestingly, the MIC value of 100 % growth inhibition of H. pylori for ACs/CuONP-5 % is equal to that of drug Clarithromycin (1.95 µg/mL). Thus, ACs/CuONPs-5 % has a promising potential as anti-H. pylori and selective anti-inflammatory agent. ACs/CuONPs-5 % is safe on the human gastric normal cells (GES-1). Therefore, amalgamation of both p-aminobenzoic acid and CuONPs into chitosan extremely promoted its anti-inflammatory and anti-H. pylori activity. This is a promising approach to achieve methods successful to compete the conventional antibiotics.

Reinforcement of the antimicrobial activity and biofilm inhibition of novel chitosan-based hydrogels utilizing zinc oxide nanoparticles.

Two novel chemically cross-linked chitosan hydrogels were successfully prepared via insertion of oxalyl dihydrazide moieties between chitosan Schiff's base chains (OCsSB) and between chitosan chains (OCs). For more modification, two different concentrations of ZnO nanoparticles (ZnONPs) were loaded into OCs to obtain OCs/ZnONPs-1 % and OCs/ZnONPs-3 % composites. The prepared samples were recognized using elemental analyses, FTIR, XRD, SEM, EDS and TEM. Their inhibitory action against microbes and biofilms were classified as: OCs/ZnONPs-3 % > OCs/ZnONPs-1 % > OCs > OCsSB > chitosan. OCs has inhibition activity similar to Vancomycin of minimum inhibitory concentration (MIC) value of 3.9 µg/mL against P. aeruginosa. OCs exhibited minimum biofilm inhibitory concentration (MBIC) values (from 31.25 to 62.5 µg/mL) less than that of OCsSB (from 62.5 to 250 µg/mL) which lower than that of chitosan (from 500 to 1000 µg/mL) against S. epidermidis, P. aeruginosa and C. albicans. OCs/ZnNPs-3 % showed MIC value (that caused 100 % inhibition of Clostridioides difficile, C. difficile) of 0.48 µg/mL much lower than Vancomycin (1.95 µg/mL). Both OCs and OCs/ZnONPs-3 % composite were safe on normal human cells. Thus, inclusion of oxalyl dihydrazide and ZnONPs into chitosan greatly reinforced its antimicrobial activity. This is a good strategy to accomplish adequate systems for competing traditional antibiotics.

Preparation and Characterization of a New Bis-Uracil Chitosan-Based Hydrogel as Efficient Adsorbent for Removal of Anionic Congo Red Dye.

A new hydrogel, based on chitosan crosslinked with 2-chlorophenyl-bis(6-amino-1,3-dimethyluracil-5-yl) methane, (2Clph-BU-Cs), has been successfully created. Various instrumental techniques such as elemental analysis, FTIR, SEM, and XRD were used to prove its structure. Its removal efficiency for anionic Congo red (CR) dye under different conditions for industrial wastewater treatment was studied. For optimizing the conditions to maximize CR dye removal, the impacts of temperature, contact time, pH, and initial concentration of the dye on adsorption capacity were investigated. The removal of the dye was pH-dependent, with a much higher value achieved at pH 4 than at pH 7 and 9. The maximum adsorption capacity of the hydrogel was 93.46 mg g-1. The model of adsorption process was fitted to the pseudo-second-order kinetic model. The intraparticle diffusion demonstrated the multi-step nature of the adsorption process. The thermodynamic results showed that the adsorption process was endothermic because of the positive value of enthalpy (43.70 kJ mol-1). The process of adsorption at high temperatures was spontaneous, according to the values of ∆G0. An increase in randomness was seen in the value of ∆S°. Generally, the investigated hydrogel has the potential to be used as a promising effective reusable adsorbent for industrial wastewater remediation.

Design, Synthesis, and Characterization of Novel Bis-Uracil Chitosan Hydrogels Modified with Zinc Oxide Nanoparticles for Boosting Their Antimicrobial Activity.

A new series of hydrogels was successfully prepared by incorporating various substituted bisuracil (R-BU) linkages between chitosan Schiff's base chains (R-BU-CsSB) and between chitosan chains (R-BU-Cs). After protection of the amino groups of chitosan by benzaldehyde, yielding chitosan Schiff's base (CsSB), the reaction with epichlorohydrin was confined on the -OH on C6 to produce epoxy chitosan Schiff's base (ECsSB), which was reacted with R-BU to form R-BU-CsSB hydrogels, and finally, the bioactive amino groups of chitosan were restored to obtain R-BU-Cs hydrogels. Further, some R-BU-Cs-based ZnO nanoparticle (R-BU-Cs/ZnONPs) composites were also prepared. Appropriate techniques such as elemental analysis, FTIR, XRD, SEM, and EDX were used to verify their structures. Their inhibition potency against all the tested microbes were arranged as: ZnONPs bio-composites > R-BU-Cs hydrogels > R-BU-CsSB hydrogels > Cs. Their inhibition performance against Gram-positive bacteria was better than Gram-negative ones. Their minimum inhibitory concentration (MIC) values decreased as a function of the negative resonance effect of the substituents in the aryl ring of R-BU linkages in the hydrogels. Compared with Vancomycin, the ZnONPs bio-composites showed superior inhibitory effects against most of the tested Gram-negative bacteria, all inspected Gram-positive ones, and all investigated fungi.

Evaluation of the antimicrobial and anti-biofilm activity of novel salicylhydrazido chitosan derivatives impregnated with titanium dioxide nanoparticles.

Two novel chitosan derivatives were prepared by incorporating salicylhydrazide into chitosan Schiff base (SCsSB) and chitosan (SCs). Two nanocomposites, SCs/TiO2-1% and SCs/TiO2-3%, were also prepared. Their structures were confirmed using elemental analyses, FTIR, XRD, SEM, EDX and TEM. Their antimicrobial and anti-biofilm activities were arranged as: SCs/TiO2-3% > SCs/TiO2-1% > SCs > SCsSB > chitosan. SCs showed minimum inhibitory concentration (MIC) value of 1.95 µg/mL against A. niger which was comparable with that of Amphotericin B. SCs/TiO2-3% showed higher inhibition against S. epidermidis, S. aureus, S. pyogenes, P. aeruginosa and E. coli than Vancomycin. While, it showed comparable inhibition activity to that of Vancomycin against B. subtilis and P. mirabilis. SCs/TiO2-3% showed MIC values equal 0.48 and 0.98 µg/mL corresponded to 0.98 and 1.95 µg/mL of Amphotericin B against C. albicans, A. fumigatus and A. niger, respectively. SCs/TiO2-3% showed much lower minimum biofilm inhibitory concentration (MBIC) values, ranged between 1.95 and 7.81 µg/mL, than those of SCs, ranged from 62.5 to 125 µg/mL. SCs/TiO2-3% was safe on normal human cells. The modifiers and TiO2 nanoparticles incorporated into chitosan in one structure developed its performance. It is approach for attaining appropriate structures which are good competitors for antimicrobial agents.

Designing, preparation and evaluation of the antimicrobial activity of biomaterials based on chitosan modified with silver nanoparticles.

Chitosan was chemically modified through a four-step procedure. First, the amino groups of chitosan have reacted with benzaldehyde (Derivative 1); second, hydroxyl groups on C6 of Derivative 1 have reacted with epichlorohydrin (Derivative 2); third, the epoxy groups of Derivative 2 have reacted with 4-aminosalicylic acid (Derivative 3); and fourth, benzaldehyde moieties of Derivative 3 have been removed to retrieve the amino groups (Derivative 4). For further modification, three nano-biocomposites were synthesized via impregnating three different concentrations of silver nanoparticles inside Derivative 4. These derivatives and Derivative 4/AgNP composites were structurally identified using elemental analysis, FTIR, XPS, 1H NMR, XRD, SEM, EDS and TEM techniques. These derivatives and Derivative 4/AgNP composites have superior antimicrobial activities than virgin chitosan. Some of them have inhibition zone analogous or superior than the utilized reference drugs. Cytotoxic activity of Derivative 4 and Derivative 4/AgNPs-5 composite indicated that these materials are safe on normal human cells. Accordingly, combinations between chitosan and functional groups derived from the different modifiers in addition to AgNPs within a single structure have extraordinarily enhanced the efficiency of chitosan. It might be deemed as a path to attain promising frameworks which are taken as proper competitors for antimicrobial materials in biomedical fields.