Optimal routine conditions for the determination of the degree of acetylation of chitosan by 1H-NMR

Enhanced porous titanium biofunctionalization based on novel silver nanoparticles and nanohydroxyapatite chitosan coatings

Titanium is widely used for implants however it presents limitations such as infection risk, stress shielding phenomenon, and poor osseointegration. To address these issues, a novel approach was proposed that involves fabricating porous titanium substrates, to reduce implant stiffness, minimizing stress shielding and bone resorption, and applying polymeric coatings to improve bioactivity. Composite coating prepared from chitosan, silver nanoparticles, and nanohydroxyapatite was optimized to enhance antibacterial properties and promote osseointegration. Chitosan with 80.5 % of deacetylation degree was used to prepare composites with diverse compositions, including different methodologies of adding silver nanoparticles, with silver concentrations below toxic level. Antibacterial activity was tested with three different strains, including Gram+ and Gram- bacteria, demonstrating excellent inhibition after 21 days. In addition, the induction of hydroxyapatite formation was investigated. Finally, the optimal porous metallic substrate that exhibited a more suitable stiffness (29 GPa) (close to the cortical bone tissue they intend to replace) was chosen to be infiltrated with the selected composites. In summary, this synergistic approach based on the combination of porous titanium substrates with 60 vol% porosity and a 355-500 μm pore size distribution coated with 3%CS-nHA-AgNPs-TPP-AgNPsbath composite provided a potential solution to provide implants with improved biomechanical balance and biofunctionality.

Structure and properties of chitosan plasticized with hydrophobic short-chain fatty acid cosolvent

The application of chitosan in packaging has always been limited due to its brittle and hygroscopic nature. In this study, hydrophobic short-chain fatty acids (SCFAs) were utilized to modify chitosan to overcome this issue. For the first time, hydrophobic SCFAs, typically hexanoic acid and its homologs, were found to be able to dissolve chitosan in water as well as its hydrophilic analog. After water was removed through evaporation, hydrophobic SCFA-modified chitosan films were obtained. The results of mechanical testing and DSC analysis confirmed that these hydrophobic SCFAs could effectively plasticize the chitosan film. Moreover, water contact angle measurements revealed that the hydrophilicity of these plasticized chitosan films was significantly reduced. The findings from the moisture uptake experiments indicated that linear hydrophobic SCFAs reduced the hygroscopicity of the chitosan film. Additionally, the crystal structures, thermal and gas barrier properties, and antibacterial activities of these hydrophobic SCFA-modified films were systematically examined and compared with those of hydrophilic SCFA-modified chitosan. This study presents an innovative and practical method for modifying chitosan films by regulating the structure of the cosolvent, thereby facilitating the real-world application of chitosan-based food packaging materials.

Physicochemical characteristics of chitosan molecules: Modeling and experiments

Chitosan, a biocompatible polysaccharide, finds a wide range of applications, inter alia as an antimicrobial agent, stabilizer of food products, cosmetics, and in the targeted delivery of drugs and stem cells. This work represents a comprehensive review of the properties of chitosan molecule and its aqueous solutions uniquely combining theoretical modeling and experimental results. The emphasis is on physicochemical aspects which were sparsely considered in previous reviews. Accordingly, in the first part, the explicit solvent molecular dynamics (MD) modeling results characterizing the conformations of chitosan molecule, the contour length, the chain diameter and the density are discussed. These MD data are used to calculate several parameters for larger chitosan molecules using a hybrid approach based on continuous hydrodynamics. The dependencies of hydrodynamic diameter, frictional ratio, radius of gyration, and intrinsic viscosity on the molar mass of molecules are presented and discussed. These theoretical predictions, comprising useful analytical solutions, are used to interpret and rationalize the extensive experimental data acquired by advanced experimental techniques. In the final part, the molecule charge, acid-base, and electrokinetic properties, comprising the electrophoretic mobility and the zeta potential, are reviewed. Future research directions are defined and discussed.

Synthesis of Schiff bases based on Chitosan, thermal stability and evaluation of antimicrobial and antitumor activities

A Schiff base of Chitosan was prepared by condensing of the Chitosan (CS) with six aromatic aldehydes and confirmed by FT-IR, NMR, XRD, TGA, and DSC. XRD results showed the disappeared of peaks at 2θ = 10° for CS and appeared one peaks at around 2θ of 23° for Schiff bases, while TGA was demonstrated that the thermal stability of CS has improved after the modification with the corresponding aldehyde. Also, DSC shows endothermal peak of CS at 100 °C due to the loss of water and second thermal event related to the decomposition of amine units with an exothermic peak at 295 °C, while Schiff bases shows endothermal peak around 70-95 °C which is related to the loss of water for all samples and the second exothermic peak around 260-280 °C is related to the decomposition of the amine group in the polymer units. The antimicrobial activities of Schiff bases were tested against + ve/ - ve Gram bacteria, and fungi, while antitumor activities were evaluated against cell lines, MCF-7, HCT-116, and HepG-2. The result shows that Schiff bases exhibited higher antimicrobial activity than Amoxycillin and Tetracycline, while Schiff bases indicated the absence of cytotoxic activity when compared to the Colchicine.

5-Fluorouracil-loaded chitosan nanoparticles conjugated with methotrexate for targeted therapy of colorectal cancer

The poor prognosis of colorectal cancer (CRC) is mainly associated with the highly invasive nature, delayed diagnosis, multidrug-resistant cells, tumor recurrence, and metastasis. Targeted therapies offer a promising means to enhance drug accumulation at the tumor site with the aid of cell-targeting ligands. Herein, chitosan-based multifunctional nanoparticles, conjugated with methotrexate (MTX) by covalent bonds, were designed for targeted delivery of 5-fluorouracil (5-FU) to improve CRC therapy. The synthesis of MTX-conjugated CS was confirmed by Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance spectroscopy (1H NMR) which showed the different degrees of CS-MTX conjugation (CS-MTX-1, CS-MTX-2 and CS-MTX-3), presenting a MTX content of 16.9, 27.5 and 30.8 %, respectively. MTX-conjugated nanoparticles containing 5-FU exhibited particle size ranged from 376.4 to 407.8 nm, high positive zeta potential and 5-FU encapsulation efficiency above 15 %. In vitro mucoadhesion assay demonstrated the mucoadhesive capacity of CS nanoparticles mainly at intestinal pH, and the conjugation of MTX to the nanoparticles reduced the mucoadhesiveness of the system, which in turn may interact specifically with tumor cells. Unconjugated and MTX-conjugated 5-FU loaded nanoparticles induced higher cytotoxic activity in HCT-116 cancer cells compared to free drugs at 24 h, with IC50 values below 27.44 μg/mL-1. Therefore, the developed systems are promising candidates as a targeted therapeutic approach for CRC treatment.

Crocin-1 laden thermosensitive chitosan-based hydrogel with smart anti-inflammatory performance for severe full-thickness burn wound therapeutics

Burns are the fourth most common type of civilian trauma worldwide, and the management of severe irregular scald wounds remains a significant challenge. Herein, crocin-1 laden hydroxybutyl chitosan (CRO-HBC) thermosensitive hydrogel with smart anti-inflammatory performance was developed for accelerating full-thickness burn healing. The injectable and shape adaptability of the CRO-HBC gel make it a promising candidate for effectively filling scald wounds with irregular shapes, while simultaneously providing protection against external pathogens. The CRO-HBC gel network formed by hydrophobic interactions exhibited an initial burst release of crocin-1, followed by a gradual and sustained release over time. The excessive release of ROS and pro-inflammatory cytokines should be effectively regulated in the early stage of wound healing. The controlled release of crocin-1 from the CRO-HBC gel adequately addresses this requirement for wound healing. The CRO-HBC hydrogel also exhibited an excellent biocompatibility, an appropriate biodegradability, keratinocyte migration facilitation properties, and a reactive oxygen species scavenging capability. The composite CRO-HBC hydrogel intelligently mitigated inflammatory responses, promoted angiogenesis, and exhibited a commendable efficacy for tissue regeneration in a full-thickness scalding model. Overall, this innovative temperature-sensitive CRO-HBC injectable hydrogel dressing with smart anti-inflammatory performance has enormous potential for managing severe scald wounds.

Measurement of the degree of deacetylation in chitosan films by FTIR, 1H NMR and UV spectrophotometry

The chitosan films were prepared from shrimp, squid, and crab to corroborate that regardless of the source of the chitosan, it was possible to measure the degree of deacetylation. In this work, the degree of deacetylation of chitosan was evaluated via UV, FTIR and 1H NMR spectrophotometry methodologies. Values in a range of 74 to 99% degree of deacetylation (DD) were obtained and varied depending on the method used and the source of chitosan. The spectrophotometric method is one of the most commonly used for this determination; however, it has the limitation that D-glucosamine and N-acetylglucosamine share similar wavelengths. All three methods were simple and provided rapid analysis; however, NMR, in particular, was expensive due to its equipment specifications. For this reason, its important to select the simplest method than can be routinely used.•The simplest used technique to determine the degree of deacetylation is infrared spectroscopy.•The degree of acetylation of chitosan is related to its physicochemical properties; its determination is an important parameter due to its association with chitosan applications in different industrial areas.•The 1H NMR method is very precise and requires expensive equipment and trained personal. Thus, it cannot be used routinely to determine the degree of deacetylation.

Multifunctional chitosan-based gel sponge with efficient antibacterial, hemostasis and strong adhesion

Developing wound dressings with solid adhesive properties that enable efficient, painless hemostasis and prevent wound infection remain a huge challenge. Herein, the tris(hydroxymethyl) methyl glycine-modified chitosan derivative (CTMG) was prepared and freeze-dried after simply adjusting the concentration of CTMG to obtain the chitosan-based gel sponge with desired multi-hollow structure, special antibacterial and biocompatibility. The adhesion strength on porcine skin was impressive up to 113 KPa, much higher than fibrin glue. It can withstand the pressure that far exceeds blood pressure. CTMG exhibits bacteriostatic abilities as demonstrated in a bacteriostatic assay, and alongside biocompatibility, as shown in cytotoxicity and hemolytic assays. Moreover, CTMG gel sponge showed hemostatic properties in both in vivo and in vitro hemostasis experiments. During an experiment on liver hemorrhage in rats, CTMG gel sponge proved to be more effective in controlling bleeding than other hemostatic sponges available on the market, indicating its promising hemostatic properties. CTMG gel sponge possesses the potential to function as a wound dressing and hemostatic material, making it suitable for various clinical applications.

Chitosan derivatives as dynamic coatings for transferrin glycoform separation in capillary electrophoresis

Chitosan and its derivatives are interesting biopolymers for different field of analytical chemistry, especially in separation techniques. The present study was aimed at testing chitosan water soluble derivatives as dynamic coating agents for application to capillary electrophoresis. In particular, chitosan was modified following three different chemical reactions (nucleophilic substitution, reductive amination, and condensation) to introduce differences in charge and steric hindrance, and to assess the effect of these physico-chemical properties in capillary electrophoresis. The effects were tested on the capillary electrophoretic separation of the glycoforms of human transferrin, an important iron-transporting serum protein, one of which, namely disialo-transferrin (CDT), is a biomarker of alcohol abuse. Chitosan derivatives were characterized by using NMR and 1H NMR, HP-SEC-TDA, DLS, and rheology. The use of these compounds as dynamic coatings in the electrolyte running buffer in capillary electrophoresis was tested assessing the peak resolution of the main glycoforms of human transferrin and particularly of disialo-transferrin. The results showed distinct changes of the peak resolution produced by the different derivatives. The best results in terms of peak resolution were achieved using polyethylene glycol (PEG)-modified chitosan, which, in comparison to a reference analytical approach, provided an almost baseline resolution of disialo-transferrin from the adjacent peaks.

Chitosan Scaffolds as Microcarriers for Dynamic Culture of Human Neural Stem Cells

Human neural stem cells (hNSCs) possess remarkable potential for regenerative medicine in the treatment of presently incurable diseases. However, a key challenge lies in producing sufficient quantities of hNSCs, which is necessary for effective treatment. Dynamic culture systems are recognized as a powerful approach to producing large quantities of hNSCs required, where microcarriers play a critical role in supporting cell expansion. Nevertheless, the currently available microcarriers have limitations, including a lack of appropriate surface chemistry to promote cell adhesion, inadequate mechanical properties to protect cells from dynamic forces, and poor suitability for mass production. Here, we present the development of three-dimensional (3D) chitosan scaffolds as microcarriers for hNSC expansion under defined conditions in bioreactors. We demonstrate that chitosan scaffolds with a concentration of 4 wt% (4CS scaffolds) exhibit desirable microstructural characteristics and mechanical properties suited for hNSC expansion. Furthermore, they could also withstand degradation in dynamic conditions. The 4CS scaffold condition yields optimal metabolic activity, cell adhesion, and protein expression, enabling sustained hNSC expansion for up to three weeks in a dynamic culture. Our study introduces an effective microcarrier approach for prolonged expansion of hNSCs, which has the potential for mass production in a three-dimensional setting.

Physicochemical and in vitro biological evaluation of an injectable self-healing quaternized chitosan/oxidized pectin hydrogel for potential use as a wound dressing material

Injectable self-healing hydrogels are attractive materials for use as wound dressings. To prepare such hydrogels, the current study used quaternized chitosan (QCS) to improve the solubility and antibacterial activity and oxidized pectin (OPEC) to introduce aldehyde groups for Schiff's base reaction with the amine groups from QCS. Self-healing hydrogels were made by co-injection of polymer solutions at specific polymer concentrations and reagent ratios that optimized both Schiff's base reactions and ionic interactions. The optimal hydrogel displayed self-healing 30 min after cutting and continuous self-healing during continuous step strain analysis, rapid gelation (< 1 min), a storage modulus of 394 Pa, and hardness of 700 mN, and compressibility of 162 mN s. The adhesiveness of this hydrogel (133 Pa) was within a suitable range for application as a wound dressing. The extraction media from the hydrogel displayed no cytotoxicity to NCTC clone 929 cells and higher cell migration than the control. While the extraction media from the hydrogel was found not to have antibacterial properties, QCS was verified as having MIC50 of 0.04 mg/mL against both E. coli and S. aureus. Therefore, this injectable self-healing QCS/OPEC hydrogel has the potential use as a biocompatible hydrogel material for wound management.

Structural and conformational changes on chitosan after green heterogeneous synthesis of phenyl derivatives

Four aromatic acid compounds: benzoic acid (Bz), 4-hydroxyphenylpropionic acid (HPPA), gallic acid (GA) and 4-aminobenzoic acid (PABA) were covalently bonded to chitosan in order to improve water solubility at neutral pH. The synthesis was performed via a radical redox reaction in heterogeneous phase by employing ascorbic acid and hydrogen peroxide (AA/H₂O₂) as radical initiators in ethanol. The analysis of chemical structure and conformational changes on acetylated chitosan was also the focus of this research. Grafted samples exhibited as high as 0.46 M degree of substitution (MS) and excellent solubility in water at neutral pH. Results showed a correlation between the disruption of C3-C5 (O3…O5) hydrogen bonds with increasing solubility in grafted samples. Spectroscopic techniques such as FT-IR and ¹H and ¹³C NMR showed modifications in both glucosamine and N-Acetyl-glucosamine units by ester and amide linkage at C2, C3 and C6 position, respectively. Finally, loss of crystalline structure of 2-helical conformation of chitosan after grafting was observed by XRD and correlated with ¹³C CP-MAS-NMR analyses.

Contribution of non-ionic interactions on bile salt sequestration by chitooligosaccharides: Potential hypocholesterolemic activity

Chitooligosaccharides have been suggested as cholesterol reducing ingredients mostly due to their ability to sequestrate bile salts. The nature of the chitooligosaccharides-bile salts binding is usually linked with the ionic interaction. However, at physiological intestinal pH range (6.4 to 7.4) and considering chitooligosaccharides pKa, they should be mostly uncharged. This highlights that other type of interaction might be of relevance. In this work, aqueous solutions of chitooligosaccharides with an average degree of polymerization of 10 and 90 % deacetylated, were characterized regarding their effect on bile salt sequestration and cholesterol accessibility. Chitooligosaccharides were shown to bind bile salts to a similar extent as the cationic resin colestipol, both decreasing cholesterol accessibility as measured by NMR at pH 7.4. A decrease in the ionic strength leads to an increase in the binding capacity of chitooligosaccharides, in agreement with the involvement of ionic interactions. However, when the pH is decreased to 6.4, the increase in charge of chitooligosaccharides is not followed by a significant increase in bile salt sequestration. This corroborates the involvement of non-ionic interactions, which was further supported by NMR chemical shift analysis and by the negative electrophoretic mobility attained for the bile salt-chitooligosaccharide aggregates at high bile salt concentrations. These results highlight that chitooligosaccharides non-ionic character is a relevant structural feature to aid in the development of hypocholesterolemic ingredients.

The novel chitosan-amphoteric starch dual flocculants for enhanced removal of Microcystis aeruginosa and algal organic matter

A novel flocculation strategy for simultaneously removing Microcystis aeruginosa and algal organic matter (AOM) was proposed using chitosan-amphoteric starch (C-A) dual flocculants in an efficient, cost-effective and ecologically friendly way, providing new insights for harmful algal blooms (HABs) control. A dual-functional starch-based flocculant, amphoteric starch (AS) with high anion degree of substitution (DS_A) and cation degree of substitution (DS_C), was prepared using a cationic moiety of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CTA) coupled with an anion moiety of chloroacetic acid onto the backbone of starch simultaneously. In combination of the results of FTIR, XPS, ¹H NMR, ¹³C NMR, GPC, EA, TGA and SEM, it was evidenced that the successfully synthesized AS with excellent structural characteristics contributed to the enhanced flocculation of M. aeruginosa. Furthermore, the novel C-A dual flocculants could achieve not only the removal of >99.3 % of M. aeruginosa, but also the efficacious flocculation of algal organic matter (AOM) at optimal concentration of (0.8:24) mg/L, within a wide pH range of 3-11. The analysis of zeta potential and cellular morphology revealed that the dual effects of both enhanced charge neutralization and notable netting-bridging played a vital role in efficient M. aeruginosa removal.

Chitosan electrospun nanofibers derived from Periplaneta americana residue for promoting infected wound healing

Periplaneta americana has been used medicinally for years to treat a wide variety of skin lesions or ulcers. However, a sizable portion of the drug residues that are retained after extraction are routinely thrown away, thus posing a hazard to the environment and depleting resources. In this study, low molecular weight Periplaneta americana chitosan (LPCS) and high molecular weight Periplaneta americana chitosan (HPCS) were extracted from Periplaneta americana residue (PAR) based on the conventional acid-base method and two deacetylation methods. Moreover, the physicochemical properties and structural differences between the above two chitosan and commercial chitosan (CS) were compared using different methods. Next, two nanofibers comprising different ratios of Periplaneta americana chitosan (LPCS or HPCS), polyvinyl alcohol (PVA), and polyethylene oxide (PEO) were prepared and optimized. The above nanofibers exhibited excellent mechanical properties, antibacterial properties, and biocompatibility while facilitating wound healing in an infected rat whole-layer wound model by promoting wound closure, epithelialization, collagen deposition, and inflammation reduction. In brief, this study produced an effective and affordable wound dressing and offered a suggestion for the comprehensive utilization of Periplaneta americana residue.

Conjugates of Chitosan with β-Cyclodextrins as Promising Carriers for the Delivery of Levofloxacin: Spectral and Microbiological Studies

In this work, we synthesized chitosan 5 kDa conjugates with β-cyclodextrins with various substituents as promising mucoadhesive carriers for the delivery of fluoroquinolones using the example of levofloxacin. The obtained conjugates were comprehensively characterized by spectral methods (UV-Vis, ATR-FTIR, 1H NMR, SEM). The physico-chemical properties of the complex formations were studied by IR, UV, and fluorescence spectroscopy. The dissociation constants of complexes with levofloxacin were determined. Complexation with conjugates provided four times slower drug release in comparison with plain CD and more than 20 times in comparison with the free drug. The antibacterial activity of the complexes was tested on model microorganisms Gram-negative bacteria Escherichia coli ATCC 25922 and Gram-positive Bacillus subtilis ATCC 6633. The complex with the conjugate demonstrated the same initial levofloxacin antibacterial activity but provided significant benefits, e.g., prolonged release.

Effect of Degree of Deacetylation of Chitosan/Chitin on Human Neural Stem Cell Culture

Stem cell therapy and research for neural diseases depends on reliable reproduction of neural stem cells. Chitosan-based materials have been proposed as a substrate for culturing human neural stem cells (hNSCs) in the pursuit of clinically compatible culture conditions that are chemically defined and compliant with good manufacturing practices. The physical and biochemical properties of chitosan and chitin are strongly regulated by the degree of deacetylation (DD). However, the effect of DD on hNSC behavior has not been systematically investigated. In this study, films with DD ranging from 93% to 14% are fabricated with chitosan and chitin. Under xeno-free conditions, hNSCs proliferate preferentially on films with a higher DD, exhibiting adherent morphology and retaining multipotency. Lowering the DD leads to formation of neural stem cell spheroids due to unsteady adhesion. The neural spheroids present NSC multipotency protein expression reduction and cytoplasmic translocation. This study provides an insight into the influence of the DD on hNSCs behavior and may serve as a guideline for hNSC research using chitosan-based biomaterials. It demonstrates the capability of controlling hNSC fate by simply tailoring the DD of chitosan.

Characterisation of products from EDC-mediated PEG substitution of chitosan allows optimisation of reaction conditions

PEGylation is a common method use to modify the physiochemical properties and increase the solubility of chitosan (CHI). Knowledge of optimal reaction conditions for PEGylation of CHI underpins its ongoing use in nanomedicine. This study synthesised methoxy polyethylene glycol grafted CHI (mPEG-CHI) using carbodiimide-mediated coupling. The effect of reagent concentrations and pH on the degree of substitution (DS) and the PEGylation yield (conversion of free PEG to conjugated PEG) was evaluated through detailed chemical characterisation. Within the parameter space investigated, optimised reaction conditions (NH₂: COOH:NHS:EDC of 3.5:1:1:10, pH = 5) resulted in a DS of 24 % and a PEGylation yield of 84 %. An EDC-derived adduct formed at pH ≥ 5.5 and a at 15-fold excess of EDC relative to COOH. The adduct was evaluated to be a guanidine derivative formed by the reaction of the amine group of CHI directly with EDC. DS ≥ 12 imparted water solubility to CHI at physiological pH and mPEG-CHI (0.2-1.0 mg/mL) was not cytotoxic against the breast cancer cell lines MCF-7 and MDA-MB-231, indicating its suitability for medical applications.

Formation, structure, properties of chitosan aspartate and metastable state of its solutions for obtaining nanoparticles

Chitosan (200 kDa) dissolution in an aqueous solution of L-aspartic acid, physicochemical properties and features of the resulting chitosan salt were studied by conductometry, potentiometry, viscometry, turbidimetry, IR and NMR spectroscopy, and X-ray diffractometry. Chitosan aspartate is a water-soluble hydrated polymorph exhibiting properties of a cationic polyelectrolyte with an effective macromolecular coil radius 60-75 nm. The specific conductivity, dielectric constant, viscosity and pH of the chitosan - L-aspartic acid - water system change over time after preparation due to counterion-polycation association to form ion pairs, multiplet structures, and their subsequent aggregation. As a result, nanoparticles (40-90 nm) are formed after ~24 h, microparticles (0.6-1.4 μm) are after ~48 h, and precipitation occurs after 72-96 h. The precipitated phase is a water-insoluble chitosan salt with a developed system of H-bonds and high crystallinity degree. Chitosan nanoparticles have high biocompatibility and the ability to accelerate the proliferative activity of epithelial cells. HYPOTHESIS: Ion pairs and multiplets are formed in the chitosan - L-aspartic acid - water system due to counterion association, which leads to phase segregation of the polymer substance at the level of nanoparticles and microparticles.

Unveiling an NMR-Invisible Fraction of Polymers in Solution by Saturation Transfer Difference

The observation of signals in solution NMR requires nuclei with sufficiently large transverse relaxation times (T₂). Otherwise, broad signals embedded in the baseline afford an invisible fraction of nuclei (IF). Based on the STD (saturation transfer difference) sequence, IF-STD is presented as a quick tool to unveil IF in the ¹H NMR spectra of polymers. The saturation of a polymer in a region of the NMR spectrum with IF (very short ¹H T₂) results in an efficient propagation of the magnetization by spin diffusion through the network of protons to a visible–invisible interphase with larger ¹H T₂ (STD_on). Subtracting this spectrum from one recorded without saturation (STD_off) produces a difference spectrum (STD_off-on), with the nuclei at the visible–invisible interphase, that confirms the presence of an IF. Analysis of a wide collection of polymers by IF-STD reveals IF more common than previously thought, with relevant IF figures when STD > 0.4% at 750 MHz. A fundamental property of the IF-STD experiment is that the signal is generated within a single state comprising polymer domains with different dynamics, as opposed to several states in exchange with different degrees of aggregation. Contrary to a reductionist visible–invisible dichotomy, our results confirm a continuous distribution of nuclei with diverse dynamics. Since nuclei observed (edited) by IF-STD at the visible–invisible interphase are in close spatial proximity to the IF (tunable with the saturation time), they emerge as a privileged platform from which gaining an insight into the IF itself.

Therapeutic effect and immune mechanism of chitosan-gentamicin conjugate on Pacific white shrimp (Litopenaeus vannamei) infected with Vibrio parahaemolyticus

To explore the disease resistance mechanism of chitosan conjugates, chitosan-gentamicin conjugate (CS-GT) was synthesized and systematically characterized, the immune mechanism of CS-GT on Litopenaeus vannamei infected with Vibrio parahaemolyticus was further explored. The results showed that imine groups in CS-GT were effectively reduced. Dietary supplementation of CS-GT can significantly increase the survival rate, total hemocyte counts, the antioxidant and immune related enzyme activity levels of shrimps (P < 0.05), which are all dose-dependent under the experimental conditions. In addition, CS-GT can protect the hepatopancreas from invading bacteria and alleviate inflammation. Particularly, CS-GT promotes the expressions of legumain (LGMN), lysosomal acid lipase (LIPA) and Niemann-Pick type C2 (NPC2) up-regulated. It is speculated that CS-GT may stimulate the lysosome to phagocytose pathogens more effectively. In conclusions, shrimps fed with CS-GT can produce immune response via lysosome and greatly improve the disease resistance to Vibrio parahaemolyticus.

Development of Chitosan-Based Surfaces to Prevent Single- and Dual-Species Biofilms of Staphylococcus aureus and Pseudomonas aeruginosa

Implantable medical devices (IMDs) are susceptible to microbial adhesion and biofilm formation, which lead to several clinical complications, including the occurrence of implant-associated infections. Polylactic acid (PLA) and its composites are currently used for the construction of IMDs. In addition, chitosan (CS) is a natural polymer that has been widely used in the medical field due to its antimicrobial and antibiofilm properties, which can be dependent on molecular weight (Mw). The present study aims to evaluate the performance of CS-based surfaces of different Mw to inhibit bacterial biofilm formation. For this purpose, CS-based surfaces were produced by dip-coating and the presence of CS and its derivatives onto PLA films, as well surface homogeneity were confirmed by contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The antimicrobial activity of the functionalized surfaces was evaluated against single- and dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa. Chitosan-based surfaces were able to inhibit the development of single- and dual-species biofilms by reducing the number of total, viable, culturable, and viable but nonculturable cells up to 79%, 90%, 81%, and 96%, respectively, being their activity dependent on chitosan Mw. The effect of CS-based surfaces on the inhibition of biofilm formation was corroborated by biofilm structure analysis using confocal laser scanning microscopy (CLSM), which revealed a decrease in the biovolume and thickness of the biofilm formed on CS-based surfaces compared to PLA. Overall, these results support the potential of low Mw CS for coating polymeric devices such as IMDs where the two bacteria tested are common colonizers and reduce their biofilm formation.

The Effect of Molecular Weight on the Antimicrobial Activity of Chitosan from Loligo opalescens for Food Packaging Applications

The growing requirement for sustainable processes has boosted the development of biodegradable plastic-based materials incorporating bioactive compounds obtained from waste, adding value to these products. Chitosan (Ch) is a biopolymer that can be obtained by deacetylation of chitin (found abundantly in waste from the fishery industry) and has valuable properties such as biocompatibility, biodegradability, antimicrobial activity, and easy film-forming ability. This study aimed to produce and characterize poly(lactic acid) (PLA) surfaces coated with β-chitosan and β-chitooligosaccharides from a Loligo opalescens pen with different molecular weights for application in the food industry. The PLA films with native and depolymerized Ch were functionalized through plasma oxygen treatment followed by dip-coating, and their physicochemical properties were assessed by Fourier-transform infrared spectroscopy, X-ray diffraction, water contact angle, and scanning electron microscopy. Their antimicrobial properties were assessed against Escherichia coli and Pseudomonas putida, where Ch-based surfaces reduced the number of biofilm viable, viable but nonculturable, and culturable cells by up to 73%, 74%, and 87%, respectively, compared to PLA. Biofilm growth inhibition was confirmed by confocal laser scanning microscopy. Results suggest that Ch films of higher molecular weight had higher antibiofilm activity under the food storage conditions mimicked in this work, contributing simultaneously to the reuse of marine waste.

Docetaxel in chitosan-based nanocapsules conjugated with an anti-Tn antigen mouse/human chimeric antibody as a promising targeting strategy of lung tumors

The aim of this work was to evaluate the physicochemical and biological properties of docetaxel (DCX) loaded chitosan nanocapsules (CS Nc) functionalized with the monoclonal antibody Chi-Tn (CS-PEG-ChiTn mAb Nc) as a potential improvement treatment for cancer therapy. The Tn antigen is highly specific for carcinomas, and this is the first time that such structure is targeted for drug delivery. The nanocapsules (Ncs), formed as a polymeric shell around an oily core, allowed a 99.9% encapsulation efficiency of DCX with a monodispersity particle size in the range of 200 nm and a high positive surface charge that provide substantial stability to the nanosystems. Release profile of DCX from Ncs showed a sustained and pH dependent behavior with a faster release at acidic pH, which could be favorable in the intracellular drug delivery. We have designed PEGylated CS Nc modified with a monoclonal antibody which recognize Tn antigen, one of the most specific tumor associated antigen. A biotin-avidin approach achieved the successful attachment of the antibody to the nanocapsules. Uptake studies and viability assay conducted in A549 human lung cancer cell line in vitro demonstrate that ChiTn mAb enhance nanoparticles internalization and cell viability reduction. Consequently, these ChiTn functionalized nanocapsules are promising carriers for the active targeting of DCX to Tn expressing carcinomas.

Supramolecular Structuring of Hyaluronan-Lactose-Modified Chitosan Matrix: Towards High-Performance Biopolymers with Excellent Biodegradation

Non-covalent interactions in supramolecular chemistry provide useful systems to understand biological processes, and self-assembly systems are suitable assets to build-up innovative products for biomedical applications. In this field, polyelectrolyte complexes are interesting, especially when polysaccharides are involved, due to their non-toxicity and bio-absorbability. In this work, we investigated a polyelectrolyte formed by hyaluronic acid (HA), a negatively charged linear polysaccharide, with Chitlac (Ch), a positively charged lactose-modified chitosan. The aim of the study was the investigation of a novel Ch–HA polyelectrolyte complex, to understand the interaction between the two polysaccharides and the stability towards enzymatic activity. By means of gel permeation chromatography–triple detector array (GPC–TDA), nuclear magnetic resonance (NMR), dynamic viscosity, Zeta Potential and scanning electron microscopy (SEM), the polyelectrolyte complex properties were identified and compared to individual polysaccharides. The complex showed monodisperse molecular weight distribution, high viscosity, negative charge, and could be degraded by specific enzymes, such as hyaluronidase and lysozyme. The results suggest a close interaction between the two polysaccharides in the complex, which could be considered a self-assembly system.

Biosynthesis of innovative calcium phosphate/hydrogel composites: physicochemical and biological characterisation

The goal of supporting and directing tissue regeneration requires the design of new, advanced materials, with features like biocompatibility, biodegradability and adequate mechanical properties. Our work was focused on developing a new injectable biomimetic composite material, based on a peptidic hydrogel and calcium phosphates with the aim of mimicking the chemical composition of natural bone tissue. Arg-Gly-Asp-grafted chitosan was used to promote cell adhesion. The obtained composite hydrogel was characterized with differential scanning calorimetry measurements, rheological analysis, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and nuclear magnetic resonance measurements. The biological responsiveness was assessed using the MG-63 human osteoblast cell line.

Synthesis of new chitosan Schiff base and its Fe2O3 nanocomposite: Evaluation of methyl orange removal and antibacterial activity

New chitosan Schiff base (3EtO-4OH/Chit) and its 3EtO-4OH/Chit/Fe₂O₃ nanocomposite were synthesized and characterized by FTIR, ¹H NMR, XRD, TGA, DSC and SEM. The result confirmed the preparation of 3EtO-4OH/Chit and its 3EtO-4OH/Chit/Fe₂O₃ nanocomposite. The efficiency of the prepared catalysts was studied for the methyl orange (MO) removal from aqueous solution. The effect of adsorbent dose and contact time on the removal of dye has been studied. Their antibacterial activities were considered against two Gram positive (S. aureus and B. cereus) and two Gram negative (E. coli and P. aeruginosa) bacteria and the results showed that the activity of the 3EtO-4OH/Chit/Fe₂O₃ is excellent and is more than chitosan and 3EtO-4OH/Chit. Thermogravimetry studies shows that the weight loss stages and the residual value at 600 °C are different for the two compounds. DSC curve of the title compounds 3EtO-4OH/Chit and 3EtO-4OH/Chit/Fe₂O₃ is different from each other. The reason for this difference could be due to the presence of iron oxide nanoparticles in 3EtO-4OH/Chit/Fe₂O₃.

Design and Synthesis of Chitosan-Gelatin Hybrid Hydrogels for 3D Printable in vitro Models

The development of 3D printable hydrogels based on the crosslinking between chitosan and gelatin is proposed. Chitosan and gelatin were both functionalized with methyl furan groups. Chemical modification was performed by reductive amination with methyl furfural involving the lysine residues of gelatin and the amino groups of chitosan to generate hydrogels with tailored properties. The methyl furan residues present in both polymers were exploited for efficient crosslinking via Diels-Alder ligation with PEG-Star-maleimide under cell-compatible conditions. The obtained chitosan-gelatin hybrid was employed to formulate hydrogels and 3D printable biopolymers and its processability and biocompatibility were preliminarily investigated.

Assessment of biological activities of chitosan Schiff base tagged with medicinal plants

A chitosan Schiff base with an aromatic aldehyde was synthesized and characterized by FTIR and NMR spectroscopies. Furthermore, the degree of substitution was calculated based on the ratios of the area of the proton of the imine (A_imine ) and the area of the peak of the proton of the pyranose ring (A_H-2 ). The antimicrobial activities were determined against bacterial and fungal strains, as well as multiple drug-resistant (MDR) bacteria. The chitosan Schiff base was also tagged with medicinal plants, for example, Curcuma longa, Peganum harmala, Lepidium sativam, and cruciferous vegetables, and the biological activities determined against pathogenic bacterial and fungal strains. The chitosan Schiff base showed maximum zone of inhibition of 22 mm against Staphylococcus aureus with a minimum zone of inhibition of 15 mm against Bacillus cereus. The chitosan Schiff base was fused with C longa, isothiocyanates and a combined mixture of P harmala and L sativam that has shown activities against Escherichia coli with a zone of inhibition of 28, 24, and 30 mm, respectively. The Schiff base of chitosan fused with medicinal plants also showed significant inhibitory activities against MDR bacteria.

Allylated chitosan-poly(N-isopropylacrylamide) hydrogel based on a functionalized double network for controlled drug release

Smart hydrogels with dual network were presented since a new allylated chitosan was conceived. As a double network hydrogel, its first network consisted of poly(N-isopropylacrylamide) worked as the gel matrix, and its second network with Schiff base bond enabled itself function as a molecular switch through the formation and break of the bond. When only the intestinal fluid was used, the second network could provide efficient protection for the loaded drug, and the drug release mechanism conformed to the non-Fickian type diffusion. While pre-treated with simulated gastric fluid, the switch would be opened and the mechanism was the Fickian type, which increased the cumulative percentage of drug release by about 25% and the release time by about 300 min. Besides, the hydrogel was characterized by ¹H NMR, FT-IR and SEM. The effects of allylated chitosan, pH and crosslinker on the swelling ratio and morphology of hydrogel were also studied.

Synthesis, characterization and antifungal efficacy of chitosan derivatives with triple quaternary ammonium groups

A novel type of water soluble chitosan derivatives (TQCSPX) were synthesized including 3-aminopyridine (TQCSP1) and 3-Amino-4-methylpyridine (TQCSP2). The theoretical structures of TQCSPX were calculated by Gaussian 09 and confirmed by FT-IR, ¹H NMR, ¹³C NMR, elemental analysis and XRD. The antifungal properties of TQCSPX against Phytophthora capsici (P. capsici), Rhizoctonia solani (R. solani), Fusarium oxysporum (F. oxysporum) and Fusarium solani (F. solani) were evaluated at concentrations ranging from 0.2mg/mL to 0.8mg/mL. Antifungal results indicated that the derivatives have significantly enhanced antifungal activity after quaternized compared with the original chitosan (CS). Moreover, TQCSP1 inhibited the growth of P. capsici with inhibitory indices of 91.94% at 0.8mg/mL. The experimental results demonstrated that the increasing number of the positive charge would improve the antifungal efficiency of chitosan, which may provide a novel direction for the development of fungicides.

Synthesis of C-coordinated O-carboxymethyl chitosan metal complexes and evaluation of their antifungal activity

Based on a condensation reaction, a chitosan-derivative-bearing amino pyridine group was prepared and subsequently followed by coordination with cupric ions, zinc ions and nickel ions to synthesize chitosan metal complexes. The calculations using the density functional theory (DFT) show that the copper ions and nickel ions underwent dsp² hybridization, the zinc ions underwent sp³ hybridization, and they all formed a coordination bond with the carbon atom in the p-π conjugate group. The antifungal properties of O-CSPX-M against Phytophthora capsici (P. capsici), Verticillium alboatrum (V. alboatrum), Botrytis cinerea (B. cinerea) and Rhizoctonia solani (R. solani) were also assayed. Apparently, chitosan metal complexes showed enhanced antifungal activity against four fungi at the tested concentrations compared to that of chitosan. It was shown that Cu complexes can inhibit the growth of P. capsici 100%, and Ni complexes can inhibit the growth of B. cinerea 77.1% at a concentration of 0.4 mg/mL and 0.2 mg/mL, respectively. The pot experiment also verified the result. In addition, the phytotoxicity experiment showed that O-CSPX-M had no obvious toxicity on wheat leaves. This kind of complexes may represent as an attractive direction for chemical modifications of metal fungicides.

Preparation and Characterization of Biocompatible Chitosan Nanoparticles for Targeted Brain Delivery of Peptides

Here, we describe a nanocarrier system that can transfer chitosan nanoparticles loaded with either small peptides such as the caspase inhibitor Z-DEVD-FMK or a large peptide like basic fibroblast growth factor across the blood-brain barrier. The nanoparticles are selectively directed to the brain and are not measurably taken up by the liver and spleen. Intravital fluorescent microscopy provides an opportunity to study the penetration kinetics of nanoparticles loaded with fluorescent agents such as Nile red. Nanoparticles functionalized with anti-transferrin antibody and loaded with peptides efficiently provided neuroprotection when systemically administered either as a formulation bearing a single peptide or a mixture of them. Failure of brain permeation of the nanoparticles after inhibition of vesicular transcytosis by imatinib as well as when nanoparticles were not functionalized with anti-transferrin antibody indicates that this nanomedicine formulation is rapidly transported across the blood-brain barrier by receptor-mediated transcytosis.

Chitosan based nano composite adsorbent-Synthesis, characterization and application for adsorption of binary mixtures of Pb(II) and Cd(II) from water

Composite type adsorbent was prepared by integrating chitosan (Cs) with crosslinked polymethacrylic acid (PMA) and nano sized halloysite nanotube (HNT). The structure of the resulting Cs-PMA/HNT adsorbents was characterized by FTIR, NMR, XRD, TGA, SEM/EDX and rheological properties. These functional adsorbents were used for removal of Pb(II) and Cd(II) as single and binary competitive mixtures from water. There was a significant improvement in adsorption properties of crosslinked PMA in the presence of Cs and HNT. The effect of synthesis parameters such as wt.% of Cs and HNT on swelling and process parameters such as solution pH, adsorbent dosage, contact time and feed concentration on adsorption of metal ions from water were studied in batch experiments. For a feed concentration of 100mg/L of metal ion, an adsorbent dose of 0.25g/L and a solution pH of 6, the Cs-PMA/HNT composite adsorbent containing 4wt% Cs and 3wt% HNT showed an adsorption capacity (mg/g)/removal% of 357.4/89.4 and 341.6/85.4 for single Pb(II) and Cd(II), respectively which reduced to 313.7/78.4 and 303.6/77.3 for the same metal ions in their binary mixtures in water.

C-coordinated O-carboxymethyl chitosan metal complexes: Synthesis, characterization and antifungal efficacy

A novel type of O-carboxymethyl chitosan Schiff bases (O-CSPX) was synthesized via a condensation reaction. After the coordination reaction of cupric ions, zinc ions and nickel ions, metal complexes (O-CSPX-M) were achieved. The theoretical structure of O-CSPX-M calculated by Gaussian 09 reveals that the copper ions and nickel ions underwent dsp² hybridization, the zinc ions underwent sp³ hybridization, and they all coordinated by the carbon atom in the p-π conjugate group. Then, the structures were confirmed by FT-IR, ¹H NMR, CP-MAS ¹³C NMR, elemental analysis, DSC and XRD. The antifungal properties of O-CSPX-M against Phytophthora capsici (P. capsici), Gibberella zeae (G. zeae), Fusarium oxysporum (F. oxysporum) and Botrytis cinerea (B. cinerea) were evaluated at concentrations ranging from 0.05mg/mL to 0.40mg/mL. The experiments indicated that the derivatives have significantly enhanced antifungal activity after metal ions complexation compared with the original chitosan. Moreover, it was shown that 0.20mg/mL of O-CSPX-Cu can 100% inhibit the growth of P. capsici and 0.20mg/mL of O-CSPX-Ni can 87.5% inhibit the growth of B. cinerea. In addition, the phytotoxicity assay and cell viability assay were also evaluated. The experimental results may provide a novel direction for the development of metal fungicides.

Optimization of high purity chitin and chitosan production from Illex argentinus pens by a combination of enzymatic and chemical processes

The present report illustrates the optimisation of the experimental conditions for the chemical and enzymatic production of chitin and chitosan from Illex argentinus pen by-products. Optima conditions for chitin isolation were established at 0.82M NaOH/36.4°C, 57.5°C/pH=9.29, 59.6°C/pH=9.30 and 49.6°C/pH=5.91 for chemical, alcalase, esperase and neutrase deproteinization, respectively. Chitin samples were subsequently deacetylated by alkaline treatment reaching the highest degrees of deacetylation (DD>93%) at 61.0-63.7% of NaOH and 14.9-16.4h of hydrolysis depending on the type of process previously performed to the squid pens. Molecular weight (as number average molecular weight, Mn) of chitosan produced in the experimental designs ranged from 143kDa (PDI 2.37) to 339kDa (PDI 2.38).