Antibacterial performance of fully biobased chitosan-grafted-polybenzoxazine films: Elaboration and properties of released material

Homogeneous films from amphiphilic hyaluronan and their characterization by confocal microscopy and nanoindentation

Self-supporting films from amphiphilic hyaluronan are suitable for medical applications like wound dressings or resorbable implants. These films are typically cast from water/alcohol solutions. However, when the mixed solvent evaporates in ambient air, convection flows develop in the solution and become imprinted in the film, potentially compromising its properties. Consequently, we developed a novel film manufacturing method: drying in a closed box under saturated vapour conditions. Using this approach, we prepared a series of optically clear lauroyl-hyaluronan (LHA) films with uniform thickness and compared them to their air-dried counterparts. We first evaluated swelling ratios and elastic moduli for LHA films with varying degrees of substitution. The box-dried films swelled significantly less and were 1-2 orders of magnitude stiffer than air-dried films from the same LHA sample. Confocal microscopy revealed that box-dried films exhibited a regular microstructure, while air-dried films displayed a pore-size gradient and strong microstructure modulation due to convection flows. Local elastic modulus variations arising from these microstructures were assessed using nanoindentation mapping. Importantly, achieving the desired film stiffness requires much lower polymer modification when box-drying is used, enhancing the biological response to the material. These findings have implications for all polysaccharide formulations that utilize mixed solvents.

Electrospun O-quaternary ammonium chitosan/polyvinyl alcohol nanofibrous film by application of Box-Behnken design response surface method for eliminating pathogenic bacteria

In this study, O-quaternary ammonium chitosan (O-HTCC) containing bicationic antibacterial active groups was synthesized to develop an O-HTCC/PVA porous nanofibrous film to enhance antibacterial activity, leveraging surface modification and nano-porous structure design. Uniform and smooth nanofibrous structures (average diameter: 72-294 nm) were successfully obtained using a simple and feasible electrospinning method. A response surface model via Box-Behnken design (BBD) was used to clarify the interaction relationship between O-HTCC fiber diameter and three critical electrospinning parameters (O-HTCC concentration, applied voltage, feed flow rate), predicting that the minimum O-HTCC fiber diameter (174 nm) could be achieved with 7 wt% of O-HTCC concentration, 14 kV of voltage, and 0.11 mL/h of feed flow rate. Linear regression (R2 = 0.9736, Radj2 = 0.9716) and the Anderson Darling test demonstrated the excellent fit of the RSM-BBD model. Compared to N-HTCC/PVA nanofibrous film, the O-HTCC/PVA version showed increased growth inhibition and more effective antibacterial efficacies against Escherichia coli (E. coli) (~;86.34 %) and Staphylococcus aureus (S. aureus) (~;99.99 %). DSC revealed improved thermal stability with an increased melting temperature (238 °C) and endothermic enthalpy (157.7 J/g). This study holds potential for further development of antibacterial packaging to extend food shelf-life to reduce bacterial infection.

Weldable, Reprocessable, and Water-resistant Polybenzoxazine Vitrimer Crosslinked by Dynamic Imine Bonds

Traditional polybenzoxazine thermosets cannot be reprocessed or recycled due to the permanent crosslinked networks. The dynamic exchangeable characteristics of imine bonds can impart the networks with reprocessabilities and recyclabilities. This study reported a weldable, reprocessable, and water-resistant polybenzoxazine vitrimer (C-ABZ) crosslinked by dynamic imine bonds. It was synthesized through a condensation reaction between an aldehyde-containing benzoxazine oligomer (O-ABZ) and 1,12-dodecanediamine. The resulting C-ABZ was able to be welded and reprocessed due to the dynamic exchange of imine bonds. The tensile strengths of the welded C-ABZ and the reprocessed C-ABZ after three cycles of hot-pressing were 76.7, 81.3, 70.8, and 58.1 Mpa, with corresponding tensile strength recovery ratios of 74.1 %, 78.6 %, 68.4 %, and 56.1 %, respectively. Furthermore, the polybenzoxazine backbone significantly improved the water resistance of the imine bonds. After immersing in water for 30 days at room temperature, the weight gain of C-ABZ was less than 1 % with corresponding tensile strength and tensile strength retention ratio of 59.5 Mpa and 57.5 %, respectively. Although the heat resistance of C-ABZ decreased slightly with increased hot-pressing cycles, a glass transition temperature (Tg, tanδ) of 150 °C was retained after the third hot-pressing. Overall, these findings demonstrate that the C-ABZ possesses excellent comprehensive performances.

A multifunctional and self-adaptive double-layer hydrogel dressing based on chitosan for deep wound repair

Hydrogel wound dressing for irregular shape and deep wound repair is a research hotspot. Herein, a multifunctional and self-adaptive double-layer hydrogel was constructed, which was comprised of chitosan-based inner layer hydrogel and gellan gum-based outer layer hydrogel. Various properties of inner layer hydrogel were systematically investigated, including injectability, shape-adaptability, solid-liquid phase transition, biocompatibility, hemostasis, antibacterial performance and anti-inflammatory. Thanks to the phase-transition from solid to liquid at body temperature, inner layer hydrogel exhibited stronger adaptability to fill irregular and deep wounds, in which chitosan was liquefied and its therapeutic effect was maximized. Outer layer hydrogel was fabricated by calcium ions and gellan gum, whose certain mechanical strength could provide protection and a moister environment for wounds. Because of these characteristics, double-layer hydrogel markedly promoted skin tissue regeneration and wound closure and thereby possessed potential clinical application prospect as wound dressing for deep wounds.

Nanocellulose-graphene composites: Preparation and applications in flexible electronics

In recent years, the pursuit of high-performance nano-flexible electronic composites has led researchers to focus on nanocellulose-graphene composites. Nanocellulose has garnered widespread interest due to its exceptional properties and unique structure, such as renewability, biodegradability, and biocompatibility. However, nanocellulose materials are deficient in electrical conductivity, which limits their applications in flexible electronics. On the other hand, graphene boasts remarkable properties, including a high specific surface area, robust mechanical strength, and high electrical conductivity, making it a promising carbon-based nanomaterial. Consequently, research efforts have intensified in exploring the preparation of graphene-nanocellulose flexible electronic composites. Although there have been studies on the application of nanocellulose and graphene, there is still a lack of comprehensive information on the application of nanocellulose/graphene in flexible electronic composites. This review examines the recent developments in nanocellulose/graphene flexible electronic composites and their applications. In this review, the preparation of nanocellulose/graphene flexible electronic composites from three aspects: composite films, aerogels, and hydrogels are first introduced. Next, the recent applications of nanocellulose/graphene flexible electronic composites were summarized including sensors, supercapacitors, and electromagnetic shielding. Finally, the challenges and future directions in this emerging field was discussed.

Benzoxazine-grafted-chitosan biopolymer films with inherent disulfide linkage: Antimicrobial properties

Synthesis and fabrication of naturally sourced biopolymers, especially chitosan, grafted with renewable small molecules have recently attracted attention as efficient antimicrobial agents and are highly desired for sustainable material development. Advantageous inherent functionalities in biobased benzoxazine extend the possibility of crosslinking with chitosan which holds immense potential. Herein, a low-temperature, greener facile methodology is adopted for the covalent confinement of benzoxazine monomers bearing aldehyde and disulfide linkages within chitosan to form benzoxazine-grafted-chitosan copolymer films. The association of benzoxazine as Schiff base, hydrogen bonding, and ring-opened structures enabled the exfoliation of chitosan galleries, and such host-guest mediated interactions demonstrated outstanding properties like hydrophobicity, good thermal, and solution stability due to the synergistic effects. Furthermore, the structures empowered excellent bactericidal properties against both E. coli and S. aureus as investigated by GSH loss, live/dead fluorescence microscopy, and morphological alteration on the cell surface by SEM. The work provides the benefits of disulfide-linked benzoxazines on chitosan, offering a promising avenue for general and eco-friendly usage in wound-healing and packaging material.

Synthesis of Bio-Based Polybenzoxazine and Its Antibiofilm and Anticorrosive Activities

Candida albicans are highly widespread pathogenic fungi in humans. Moreover, its developed biofilm causes serious clinical problems, leading to drug failure caused by its inherent drug tolerance. Hence, the inhibition of biofilm formation and virulence characteristics provide other means of addressing infections. Polymer composites (PCs) derived from natural products have attracted increasing interest in the scientific community, including antimicrobial applications. PCs are a good alternative approach to solving this challenge because of their excellent penetration power inside biofilms. The main objectives of this study were to synthesize a novel curcumin-based polybenzoxazine polymer composite (poly(Cu-A) PC) using Mannich condensation reaction and evaluate their potency as an antibiofilm and anticorrosive candidate against C. albicans. In addition, their anticorrosive efficacy was also explored. PC exhibited significant antibiofilm efficacy versus C. albicans DAY185 by the morphologic changing of yeast to hyphae, and>90% anticorrosive efficacy was observed at a higher dose of PC. These prepared PC were safe in vivo against Caenorhabditis elegans and Raphanus raphanistrum. The study shows that a polybenzoxazine polymer composite has the potential for controlling biofilm-associated fungal infections and virulence by C. albicans, and opens a new avenue for designing PCs as antifungal, anticorrosive agents for biofilm-associated fungal infections and industrial remediation.

Chitosan-Urushiol nanofiber membrane with enhanced acid resistance and broad-spectrum antibacterial activity

Due to the large specific surface area and rich pore structure, chitosan nanofiber membrane has many advantages over conventional gel-like or film-like products. However, the poor stability in acidic solutions and relatively weak antibacterial activity against Gram-negative bacteria severely restrict its use in many industries. Here, we present a chitosan-urushiol composite nanofiber membrane prepared by electrospinning. Chemical and morphology characterization revealed that the formation of chitosan-urushiol composite involved the Schiff base reaction between catechol and amine groups and the self-polymerization of urushiol. The unique crosslinked structure and multiple antibacterial mechanisms endowed the chitosan-urushiol membrane with outstanding acid resistance and antibacterial performance. After immersion in HCl solution at pH 1, the membrane maintained its intact appearance and satisfactory mechanical strength. In addition to its good antibacterial performance against Gram-positive Staphylococcus aureus (S. aureus), the chitosan-urushiol membrane exhibited synergistic antibacterial activity against Gram-negative Escherichia coli (E. coli) that far exceeded that of neat chitosan membrane and urushiol. Moreover, cytotoxicity and hemolysis assays revealed that the composite membrane had good biocompatibility similar to that of neat chitosan. In short, this work provides a convenient, safe, and environmentally friendly method to simultaneously enhance the acid resistance and broad-spectrum antibacterial activity of chitosan nanofiber membranes.

Ring-Opening Oligomerization Mechanism of a Vanillin-Furfurylamine-Based Benzoxazine and a Mono-Azomethine Derivative

Exploring the ring-opening polymerization (ROP) mechanism of benzoxazines is a fundamental issue in benzoxazine chemistry. Though some research papers on the topic have been reported, the ROP mechanism of mono-benzoxazines is still elusive. The key point for mechanistic studies is to determine and characterize the structure and formation pathways of the products generated in ROP. In this paper, the ROP of a vanillin-furfurylamine-based benzoxazine and a mono-azomethine derivative is studied with differential scanning calorimetry, fourier transform infrared spectroscopy, nuclear magnetic resonance, and electrospray ionization mass spectrometry, respectively. The results show that the products consist of a range of cationic species, zwitterions, fragments, and series of cyclic and linear oligomers of varying molecular sizes. It is proposed that both mono-benzoxazines undergo thermally activated cationic ring-opening oligomerization via zwitterion intermediates. Upon thermal induction, multi-bond-cleavage takes place to form various zwitterionic intermediates, which react with a monomer, a fragment, or a second zwitterion by several pathways to generate cyclic and linear oligomers.

Metal Complexes of the Porphyrin-Functionalized Polybenzoxazine

New porphyrin-functionalized benzoxazine (Por-BZ) in high purity and yield was synthesized in this study based on ¹H and ¹³C NMR and FTIR spectroscopic analyses through the reduction of Schiff base formed from tetrakis(4-aminophenyl)porphyrin (TAPP) and salicylaldehyde and the subsequent reaction with CH₂O. Thermal properties of the product formed through ring-opening polymerization (ROP) of Por-BZ were measured using DSC, TGA and FTIR spectroscopy. Because of the rigid structure of the porphyrin moiety appended to the benzoxazine unit, the temperature required for ROP (314 °C) was higher than the typical Pa-type benzoxazine monomer (ca. 260 °C); furthermore, poly(Por-BZ) possessed a high thermal decomposition temperature (T_d10 = 478 °C) and char yield (66 wt%) after thermal polymerization at 240 °C. An investigation of the thermal and luminescence properties of metal–porphyrin complexes revealed that the insertion of Ni and Zn ions decreased the thermal ROP temperatures of the Por-BZ/Ni and Por-BZ/Zn complexes significantly, to 241 and 231 °C, respectively. The metal ions acted as the effective promoter and catalyst for the thermal polymerization of the Por-BZ monomer, and also improved the thermal stabilities after thermal polymerization.

Synthesis and Characterization of Sulfur and Sulfur-Selenium Nanoparticles Loaded on Reduced Graphene Oxide and Their Antibacterial Activity against Gram-Positive Pathogens

Resistance to antimicrobial agents in Gram-positive bacteria has become a major concern in the last decade. Recently, nanoparticles (NP) have emerged as a potential solution to antibiotic resistance. We synthesized three reduced graphene oxide (rGO) nanoparticles, namely rGO, rGO-S, and rGO-S/Se, and characterized them using X-ray diffraction (PXRD), Raman analysis, and thermogravimetric analysis. Transmission electron microscopy confirmed spherical shape nanometer size S and S/Se NPs on the rGO surface. Antibacterial properties of all three nanomaterials were probed against Gram-positive pathogens Staphylococcus aureus and Enterococcus faecalis, using turbidometeric and CFU assays. Among the synthesized nanomaterials, rGO-S/Se exhibited relatively strong antibacterial activity against both Gram-positive microorganism tested in a concentration dependent manner (growth inhibition >90% at 200 μg/mL). Atomic force microscopy of rGO-S/Se treated cells displayed morphological aberrations. Our studies also revealed that rGO composite NPs are able to deposit on the bacterial cell surface, resulting in membrane perturbation and oxidative stress. Taken together, our results suggest a possible three-pronged approach of bacterial cytotoxicity by these graphene-based materials.

Self-Polymerization Promoting Monomers: In Situ Transformation of Disulfide-Linked Benzoxazines into the Thiazolidine Structure

Polybenzoxazines obtained especially from green synthons are facing challenges of the requirement of high ring-opening polymerization (ROP) temperature of the monomer, thus affecting their exploration at the industrial front. This demands effective structural changes in the monomer itself, to mediate catalyst-free polymerization at a low energy via one-step synthesis protocol. In this regard, monomers based on disulfide-linked bisbenzoxazine were successfully synthesized using cystamine (biobased) and cardanol (agro-waste)/phenol. Reduction of the disulfide bridge in the monomer using dithiothreitol under mild conditions in situ transformed the oxazine ring in the monomer, via neighboring group participation of the -SH group in a transient intermediate monomer, into a thiazolidine structure, which is otherwise difficult to synthesize. Structural transformation of ring-opening followed by the ring-closing intramolecular reaction led to an interconversion of O-CH₂-N containing a six-membered oxazine ring to S-CH₂-N containing a five-membered thiazolidine ring and a phenolic-OH. The structure of the monomer with the oxazine ring and its congener with the thiazolidine ring was characterized by spectroscopic methods and X-ray analysis. Kinetics of structural transformation at a molecular level is studied in detail, and it was found that the reaction proceeded via a transient 2-aminoethanethiol-linked benzoxazine intermediate, as supported by nuclear magnetic resonance spectroscopy and density functional theory studies. The thiazolidine-ring-containing monomer promotes ROP at a substantially low temperature than the reported mono-/bisoxazine monomers due to the dual mode of facilitation of the ROP reaction, both by phenolic-OH and by ring strain. Surprisingly, both the monomer structures led to the formation of a similar polymer structure, as supported by thermogravimetric analysis and Fourier transform infrared study. The current work highlights the benefits of inherent functionalities in naturally sourced feedstocks as biosynthons for the new latest generation of benzoxazine monomers.

Potential Effects of Phenolic Compounds That Can Be Found in Olive Oil on Wound Healing

The treatment of tissue damage produced by physical, chemical, or mechanical agents involves considerable direct and indirect costs to health care systems. Wound healing involves a series of molecular and cellular events aimed at repairing the defect in tissue integrity. These events can be favored by various natural agents, including the polyphenols in extra virgin olive oil (EVOO). The objective of this study was to review data on the potential effects of different phenolic compounds that can also be found in EVOO on wound healing and closure. Results of in vitro and animal studies demonstrate that polyphenols from different plant species, also present in EVOO, participate in different aspects of wound healing, accelerating this process through their anti-inflammatory, antioxidant, and antimicrobial properties and their stimulation of angiogenic activities required for granulation tissue formation and wound re-epithelialization. These results indicate the potential usefulness of EVOO phenolic compounds for wound treatment, either alone or in combination with other therapies. Human studies are warranted to verify this proposition.

Synthesis and characterization of a novel benzothiazole functionalized chitosan and its use for effective adsorption of Cu(II)

Contamination of water with the copper(II) ions leads to serious diseases such as liver damage and cancer. This deadly effect prompted us to target the synthesis of a novel functionalized chitosan (Cs-BT) to be used as an adsorbent for removing the copper(II) ions from the aqueous solution. The functionalization was done by introducing benzothiazole moiety into the chitosan (Cs) chain and confirmed by the full disappearance of the NH₂ band in the FT-IR spectrum of the adsorbent. The TGA-DTG analysis revealed that the functionalization reduced the thermal stability of the adsorbent (Cs-BT) as compared with pure chitosan. The adsorption was evidenced by SEM and EDX analysis. The adsorption study demonstrated that the optimal adsorption conditions were 120 min contact time, pH = 6, and initial Cu(II) concentration 200 mg/L. At these conditions, the Cs-BT achieved a maximum copper adsorption capacity of 1439.7 mg/g. Consequently, Cs-BT could be a promising and efficient Cu adsorbent in water treatment. Study the adsorption kinetics and isotherms manifested that the pseudo-first-order was better than pseudo-second-order and Temkin isotherm was better than Langmuir, Freundlich, and Dubinin-Radushkevich for explaining the adsorption process. The calculated thermodynamic parameters implied the spontaneity and the endothermic nature of the adsorption process.

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

Heat-resistant and robust biobased benzoxazine resins developed with a green synthesis strategy

Two high-performance biobased benzoxazine resins from mono-phenols are developed with a green synthesis strategy.