Photosensitive Polymeric Janus Micromotor for Enzymatic Activity Protection and Enhanced Substrate Degradation.

Immobilizing enzymes into microcarriers is a strategy to improve their long-term stability and reusability, hindered by (UV) light irradiation. However, in such approaches, enzyme-substrate interaction is mediated by diffusion, often at slow kinetics. In contrast, enzyme-linked self-propelled motors can accelerate this interaction, frequently mediated by the convection mechanism. This work reports on a new photosensitive polymeric Janus micromotor (JM) for UV-light protection of enzymatic activity and efficient degradation of substrates accelerated by the JMs. The JMs were assembled with UV-photosensitive modified chitosan, co-encapsulating fluorescent-labeled proteins and enzymes as models and magnetite and platinum nanoparticles for magnetic and catalytic motion. The JMs absorbed UV light, protecting the enzymatic activity and accelerating the enzyme-substrate degradation by magnetic/catalytic motion. Immobilizing proteins in photosensitive JMs is a promising strategy to improve the enzyme's stability and hasten the kinetics of substrate degradation, thereby enhancing the enzymatic process's efficiency.

Non-cell adhesive hexanoyl glycol chitosan hydrogels for stable and efficient formation of 3D cell spheroids with tunable size and density.

Three-dimensional (3D) culture systems that provide a more physiologically similar environment than conventional two-dimensional (2D) cultures have been extensively developed. Previously we have provided a facile method for the formation of 3D spheroids using non-adhesive N-hexanoyl glycol chitosan (HGC) hydrogel-coated dishes, but with limitations such as low gel stability and weak mechanical properties. In this study, chemically crosslinked hydrogels were prepared by photocrosslinking of methacrylated HGCs (M-HGCs), and their spheroid-forming abilities were evaluated for long-term 3D cell cultures. The M-HGC hydrogels demonstrated not only enhanced gel stability, but also good spheroid-forming abilities. Furthermore, the M-HGC-coated dishes were effective in generating spheroids of larger size and higher cell density depending on the crosslinking density of the M-HGCs. These results indicate that our hydrogel-coated dish system could be widely applied as an effective technique to produce cell spheroids with customized sizes and densities that are essential for tissue engineering and drug screening.

Preparation of low molecular chitosan by microwave-induced plasma desorption/ionization technology.

Compared with high molecular weight chitosan (HMWC), low molecular weight chitosan (LMWC) has better solubility and biological activity. However, there is no quick and environmentally friendly to prepare low molecular chitosan. In this study, microwave induced plasma desorption/ionization (MIPDI) was used for the first time to prepare LMWC through the degradation processes of HMWC. The results showed that MIPDI has the most abundant ∙OH content at the gas-liquid interface, and the active particles represented by ∙OH can degrade chitosan with a molecular weight of 540 KDa into soluble chitosan (≤ 10 KDa), and the yield of soluble chitosan can reach 61% in 60 min. Moreover, a series of characterization results showed that the chain structure and crystal structure gradually degraded as the treatment time increased while the chemical structure of chitosan did not change significantly. Antibacterial experiments also indicated that the antimicrobial property of LMWC obtained by MIPDI degradation was improved. In short, this method has proven to be a new, fast and green processing method for the preparation of low molecular chitosan.

Chitosan/boron nitride nanobiocomposite films with improved properties for active food packaging applications.

Chitosan (CS)/boron nitride nanoplatelet (BNNP) nanobiocomposite films were successfully prepared. Morphological results showed good dispersion of BNNPs in the CS matrix. After loading with BNNPs, water solubility (WS) and moisture absorption of the CS film decreased. The WS decreased from 41.2 to 27.8% at 7 wt% BNNP loading. Additionally, water vapor permeation decreased from 4.2 × 10-11 for pure CS film to 2.9 × 10-11 g m-1s-1Pa-1 at 7 wt% BNNP inclusion. The oxygen permeability of CS film decreased by up to 84% at 7 wt% BNNP loading. The composites showed better sodium hydroxide resistance compared with pure CS. Thermal stability of the composites was higher than the pure CS, up to 35 °C increase at 7 wt% BNNP loading. The addition of 5 wt% BNNPs improved Young's modulus by up to 45% compared with pure CS film. Cytotoxicity of the films decreased after loading with BNNPs.

A new antibacterial nano-system based on hematoporphyrin-carboxymethyl chitosan conjugate for enhanced photostability and photodynamic activity.

To promote bactericidal activity, improve photostability and safety, novel antibacterial nanoparticle system based on photodynamic action (PDA) was prepared here through conjugation of photosensitizer hematoporphyrin (HP) onto carboxymethyl chitosan (CMCS) via amide linkage and followed by ultrasonic treatment. The system was stable in PBS (pH 7.4) and could effectively inhibit the photodegradation of conjugated HP because of aggregation-caused quenching effect. ROS produced by the conjugated HP under light exposure could change the structure of nanoparticles by oxidizing the CMCS skeleton and thereby significantly promote the photodynamic activity of HP and its photodynamic activity after 6 h was higher than that of HP·2HCl under the same conditions. Antibacterial experiments showed that CMCS-HP nanoparticles had excellent photodynamic antibacterial activity, and the bacterial inhibition rates after 60 min of light exposure were greater than 97%. Safety evaluation exhibited that the nanoparticles were safe to mammalian cells, showing great potential for antibacterial therapy.

Antibacterial functionalization of cotton and cotton/polyester fabrics applying hybrid coating of copper/chitosan nanocomposites loaded polymer blends via gamma irradiation.

In the present work, copper/chitosan nanocomposites (Cu/CS) were prepared in an aqueous solution in the presence of CS as stabilizer and CuSO4·5H2O precursor. The Cu/CS NPs formation was proved through transmission electron microscopy (TEM), Dynamic light scattering (DLS), Fourier Transform infrared (FT-IR) spectroscopy and XRD diffraction. Cotton and cotton/polyester fabrics were gamma-radiation grafted by padding to pickup of 100%, in nanocomposites based on Cu/CS NPs loaded in polymer blends of poly(vinyl alcohol) (PVA) and plasticized starch (PLST). The grafted fabrics were characterized in terms of tensile mechanical, crease recovery and water absorption properties. The results showed that cotton fabrics displayed higher water absorption (%) than cotton/polyester fabrics for all PVA/PLST compositions and water absorption was found to decrease with increasing the ratio of PVA in the PVA/PLST blends. Cotton/polyester fabrics displays crease recovery angle (CRA) value of 147.6 upon treated with PVA/PLST (80/20%) and gamma irradiated to 30 kGy compared to CRA value of 125.0 for cotton fabrics treated under the same conditions. For cotton fabrics, the tensile strength was largely depends on the irradiation dose, in which the tensile strength of the treated fabric with the different formulations is higher than the untreated fabric. The antimicrobial activity of the fabrics against gram-positive bacteria (Staphylococcus aurous) and gram-negative bacteria (Escherichia coli) was investigated. In case of gram-positive bacteria cotton fabric showed the highest impact, for both 50/50 and 20/80 PVA/PLST of 14 and 14.5 mm inhibition zone, whilst, cotton/polyester fabric recorded 6 and 5 mm inhibition zone against gram-negative bacteria for 50/50 and 20/80 PVA/PLST, respectively.

Use of gamma irradiation technology for modification of bacterial cellulose nanocrystals/chitosan nanocomposite film.

The objective of this work was to investigate the influence of different gamma ray dosages (5, 10, and 10 kGy) on the structural, mechanical, surface and barrier properties of chitosan (Ch) based nanocomposite film. The results showed gamma irradiation caused an increase in the surface hydrophobicity, water vapor permeability and sensitivity of films to water and also, yellowness and opacity of films increased, simultaneously. By increasing the irradiation doses up to 10 kGy, the mechanical properties of Ch/BCNC film was significantly enhanced. As observed by FTIR spectra, no change occurred in the chemical functional groups of the films during irradiation. XRD studies confirmed that crystallinity of films was increased after irradiation. The nanocomposite film irradiated by 10 kGy had the highest thermal stability. In conclusion, gamma radiation can be considered as a safe method for sterilization of foods and modification of Ch/BCNC film properties.

Chitosan: Structural modification, biological activity and application.

Many by-products that are harmful to the environment and human health are generated during food processing. However, these wastes are often potential resources with high-added value. For example, crustacean waste contains large amounts of chitin. Chitin is one of the most abundant polysaccharides in natural macromolecules, and is a typical component of crustaceans, mollusks, insect exoskeleton and fungal cell walls. Chitosan is prepared by deacetylation of chitin and a copolymer of D-glucosamine and N-acetyl-D-glucosamine through ß-(1 â†’ 4)-glycosidic bonds. Chitosan has better solubility, biocompatibility and degradability compared with chitin. This review introduces the preparation, physicochemical properties, chemical and physical modification methods of chitosan, which could help us understand its biological activities and applications. According to the latest reports, the antibacterial activity, antioxidant, immune and antitumor activities of chitosan and its derivatives are summarized. Simultaneously, the various applications of chitosan and its derivatives are reviewed, including food, chemical, textile, medical and health, and functional materials. Finally, some insights into its future potential are provided, including novel modification methods, directional modification according to structure-activity relationship, activity and application development direction, etc.

Crosslinked chitosan embedded TiO2 NPs and carbon dots-based nanocomposite: An excellent photocatalyst under sunlight irradiation.

Herein, a new hybrid nanocomposite, comprising of titania nanoparticles (TiO2 NPs) and carbon dots (CDs) deposited polyvinyl imidazole crosslinked chitosan [cl-Ch-p(VI)/TiO2NPs-CDs] has been developed. The nanocomposite has been synthesised by in-situ deposition of TiO2 NPs and CDs onto the surface of the copolymer under microwave irradiation. To the best of our knowledge, this in-situ approach has effectively been applied for the first time to fabricate green fluorescent CDs from sugar cane juice at moderate temperature (75 °C) under microwave irradiation. The developed nanocomposite has been characterized using UV-Vis spectroscopy, 13C NMR, XRD, HR-TEM, STEM and XPS analyses. The results suggest that the successful deposition of TiO2 NPs and CDs onto the surface of crosslinked chitosan is achieved. The experimental studies indicate that the NPs/CDs-impregnated nanocomposite allows efficient photocatalytic degradation of toxic organic compounds (~98.6% degradation of 2,4-dicholorophenol, ~95.8% degradation of Reactive Blue 4, ~98.2% degradation of Reactive Red 15) in the presence of sunlight. Finally, LC-MS analysis of the resultant degraded materials reveals the formation of organic molecules with lower molecular mass.

Eco-biocompatibility of chitosan coated biosynthesized copper oxide nanocomposite for enhanced industrial (Azo) dye removal from aqueous solution and antibacterial properties.

In the present study, the biogenic synthesis of an ecofriendly and non-toxic chitosan (CS) coated copper oxide NPs (CS-CuO nanocomposite) using Psidium guajava aqueous leaf extract. The biogenic synthesized CS-CuO nanocomposite was characterized by using UV-vis spectroscopy analysis (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FE-SEM-EDS), Dynamic light scattering (DLS), and Transmission electron microscopy (TEM). The prepared CS-CuO nanocomposite was evaluated for antibacterial activity by agar well diffusion method as well as minimum inhibitory concentrations (MIC) were assessed against both Gram-positive Streptococcus pneumoniae, Staphylococcus epidermidis and Gram-negative Escherichia coli, Proteus mirabilis with good inhibition effects on Gram-negative bacteria than the Gram-positive bacteria. The interaction of the CS-CuO nanocomposite with the bacterial membrane was visually observed by confocal laser scanning microscopy and the live/dead cells were differentiated by treatment with acridine orange and ethidium bromide dyes.

High-efficient and synergetic antibacterial nanocomposite hydrogel with quaternized chitosan/Ag nanoparticles prepared by one-pot UV photochemical synthesis.

Hydrogel dressings have significant advantages such as absorption of tissue exudate, maintenance of proper moist environment, and promotion of cell proliferation. However, facile preparation method and high-efficient antibacterial hydrogel dressings are still a great challenge. In this study, a facile approach to prepare antibacterial nanocomposite hydrogel dressing to accelerate healing was explored. The hydrogels consisted of quaternized chitosan and chemically cross-linked polyacrylamide, as well as silver nanoparticles (AgNPs) stabilized by chitosan. The synthesis of the hydrogels including the formation of AgNPs and polymerization of acrylamide was accomplished simultaneously under UV irradiation in 1 hour without adding initiator. The hydrogels showed favorable tensile strength of ∼100 kPa with elongation at break over 1000% and shear modulus of ∼104 Pa as well as suitable swelling ratio, which were appropriate for wound dressing. The combination of quaternized chitosan and AgNPs exhibited high-efficient and synergetic antibacterial performance with low cytotoxicity. In vivo animal experiments showed that the hydrogel can effectively prevent wound infection and promote wound healing. This study provides a facile method to produce antibacterial hydrogel wound dressing materials.

Novel heterocyclic chitosan derivatives and their derived nanoparticles: Catalytic and antibacterial properties.

The metal-assisted nitrone-nitrile cycloaddition reaction is apply to empower chitosan chemistry. The ultrasonic irradiation has proven to efficiently accelerate the cycloaddition affording new heterocyclic (1,2,4-oxadiazoline) chitosan derivatives and avoiding ultrasonic degradation of the chitosan macromolecules. By varying the nitrone nature, both water- and toluene-soluble chitosan derivatives were successfully synthesized. Relying on the ionic gelation approach nanoparticles of heterocyclic chitosan derivatives were prepared. Water-soluble chitosan derivative demonstrated a high antibacterial activity coupled with low toxicity. The toxicity of the synthesized heterocyclic chitosan derivatives and their based nanoparticles are comparable with those of the starting chitosan, while their antibacterial activity is superior. Toluene-soluble derivatives are shown to be efficient homogeneous catalysts towards monoglyceride synthesis via the epoxide ring opening. They efficiently catalyze selective conversion of fatty acids and glycidol into corresponding monoglycerides allowing one to simplify significantly the procedure for separating the reaction product from the catalyst for its recovery and reusage.

Gamma rays induced acquisition of structural modification in chitosan boosts photosynthetic machinery, enzymatic activities and essential oil production in citronella grass (Cymbopogon winterianus Jowitt).

Oligomers derived through irradiation of marine polysaccharides have generated a lot of interest of plant biologists as the application of these molecules has yielded positive results regarding various plant processes. To comprehend the previously established growth-promoting activity of irradiated chitosan (ICH) and to gain insight of the structure-property relationship, gamma rays induced structural changes were analyzed using techniques such as Fourier Transform Infrared (FT-IR) spectroscopy, Ultraviolet-visible (UV-Vis) spectroscopy, 13C-Nuclear Magnetic Resonance (NMR) spectroscopy and Scanning Electron Microscopy (SEM). Moreover, to study the bioactivity of ICH samples a pot experiment was conducted on citronella grass (Cymbopogon winterianus) to access its response to foliar application of various levels (40, 60, 80 and 100 mg L-1) of ICH in terms of growth, physiological attributes and essential oil (EO) production. The application of ICH at 80 mg L-1(ICH-80) resulted in the maximum values of most of the attributes studied. Due to this treatment, the maximum improvement in the content (29.58%) and yield (90.81%) of EO in Cymbopogon winterianus were achieved. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that ICH-80 also increased the content of citronellal (14.81%) and geraniol (18.15%) of the EO as compared to the control.

A shear-thinning adhesive hydrogel reinforced by photo-initiated crosslinking as a fit-to-shape tissue sealant.

Surgical sealants suitable for wounds with non-flat complex geometries are still a challenge to fulfill clinical requirements. Herein, a novel fit-to-shape sealant enhanced by photo-initiated crosslinking was developed utilizing maleic anhydride modified chitosan (MCS), benzaldehyde-terminated PEG (PEGDF) and polyethylene glycol diacrylate (PEGDA). Initially, the shear-thinning hydrogel prepared through the Schiff-base linkage between MCS and PEGDF could be injected into target sites, remolded to conform to a wound with non-flat complex geometry, and remain on the wound, avoiding adverse liquid leakage. Under illumination with ultra-violet (UV) light, the hydrogel was solidified in situ rapidly to adopt the wound contour and enhanced in adhesive strength to seal defects of the tissue. In addition, the hydrogel exhibits stability in extreme pH environments (pH = 1) and has potential to treat wounds inside the stomach with the existence of gastric acid. Moreover, the hydrogel can be applied as adhesive wound dressings through in situ 3D printing. Taken together, the fit-to-shape sealant enhanced by photo-initiated crosslinking can be considered as promising tissue adhesives for wound closure and other biomedical applications.

Photoinduced chitosan-PEG hydrogels with long-term antibacterial properties.

Photochemical processes offer the possibility of preparing functional hydrogels under green conditions that are compatible with both synthetic and natural polymers. In this study, chitosan-based poly(ethylene) glycol (PEG) were successfully synthesized under light irradiation in aqueous medium. Kinetic studies under irradiation showed that less than 2 min were necessary to obtain fully cross-linked networks. Thermomechanical analyses and swelling experiments indicated that introduction of chitosan overall weakens the hydrogel network but can create domains of higher thermal stability than the PEG-alone structure. The resulting chitosan-PEG hydrogels demonstrated a tremendous inhibition (100%) of bacterial growth (Escherichia coli and Staphylococcus aureus). After 6 months' ageing, one of the hydrogels preserved a high antifouling activity against Escherichia coli. This interesting result, which could be correlated with the network features, demonstrates the strong potential of these photochemical methods to obtain robust bio-functional materials.

Characterization of bacterial cellulose films combined with chitosan and polyvinyl alcohol: Evaluation of mechanical and barrier properties.

Bacterial cellulose (BC) produced by Komagataeibacter xylinus is a biomaterial with a unique three-dimensional structure. To improve the mechanical properties and reinforce the BC films, they were immersed in polyvinyl alcohol (0-4%) and chitosan (0-1%) baths. Moisture content, mechanical properties and water vapour permeability were measured to assess the effect of polyvinyl alcohol and chitosan. The morphology, optical, structural and thermal properties were evaluated by scanning electron microscopy, spectral analysis, thermogravimetry and differential scanning calorimetry. Results showed that moisture content was significantly affected by the chitosan presence. Tensile strength values in the 20.76-41.65 MPa range were similar to those of synthetic polymer films. Percentage of elongation ranged from 2.28 to 21.82% and Young's modulus ranged from 1043.88 to 2247.82 MPa. The water vapour permeability (1.47 × 10-11-3.40 × 10-11 g/m s Pa) decreased with the addition of polyvinyl alcohol. The developed films own UV light barrier properties and optimal visual appearance.

Crosslinking of chitosan films processed by compression molding.

An alternative approach towards more sustainable chitosan films, through their manufacture by thermo-compression molding, was explore in this work. This strategy permitted the reduction of production times and avoided the use of organic solvents since biopolymer and acid were mixed in their solid form. Furthermore, the acid used as a crosslinker was citric acid, a natural policarboxylic acid, which promoted the reaction with chitosan, as shown by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). This crosslinking reaction led to the formation of homogeneous structures, as observed by scanning electron microscopy (SEM), indicating a good compatibility among all the components of the mixture and enhancing the mechanical properties of the resulting films. In particular, an increase of 80% for tensile strength and an increase of 3000% for elongation at break were observed for the crosslinked films. In addition to the homogeneous surface of citric acid-incorporated films, all the films showed hydrophobic character and the addition of citric acid led to a more amorphous structure. In sum, citric acid-incorporated chitosan films manufactured by compression molding were found to show potential for food and pharmaceutical applications.

Light controllable chitosan micelles with ROS generation and essential oil release for the treatment of bacterial biofilm.

Bacterial biofilms are widely associated with persistent infections and food contamination. High resistance to conventional antimicrobial agents resulted in an urgent need for novel formulation to eliminate these bacterial communities. Herein we fabricated light controllable chitosan micelles loading with thymol (T-TCP) for elimination of biofilm. Due to the exterior chitosan, T-TCP micelles easily bind to negative biofilm through electrostatic interaction and efficiently deliver the essential oil payloads. Under irradiation, T-TCP micelles generated ROS, which triggered simultaneous thymol release and also resulted in additional ROS-inducing bactericidal effects, both effectively eradicating biofilms of Listeria monocytogenes and Staphylococcus aureus. This formulation provided a platform for other water-insoluble antimicrobials and might be used as a potent and controllable solution to biofilm fighting.

Shining Light on Chitosan: A Review on the Usage of Chitosan for Photonics and Nanomaterials Research.

Chitosan (CS) is a natural polymer derived from chitin that has found its usage both in research and commercial applications due to its unique solubility and chemical and biological attributes. The biocompatibility and biodegradability of CS have helped researchers identify its utility in the delivery of therapeutic agents, tissue engineering, wound healing, and more. Industrial applications include cosmetic and personal care products, wastewater treatment, and corrosion protection, to name a few. Many researchers have published numerous reviews outlining the physical and chemical properties of CS, as well as its use for many of the above-mentioned applications. Recently, the cationic polyelectrolyte nature of CS was found to be advantageous for stabilizing fascinating photonic materials including plasmonic nanoparticles (e.g., gold and silver), semiconductor nanoparticles (e.g., zinc oxide, cadmium sulfide), fluorescent organic dyes (e.g., fluorescein isothiocyanate (FITC)), luminescent transitional and lanthanide complexes (e.g., Au(I) and Ru(II), and Eu(III)). These photonic systems have been extensively investigated for their usage in antimicrobial, wound healing, diagnostics, sensing, and imaging applications. Highlighted in this review are the different works involving some of the above-mentioned molecular-nano systems that are prepared or stabilized using the CS polymer. The advantages and the role of the CS for synthesizing and stabilizing the above-mentioned optically active materials have been illustrated.