Self-coacervation of carboxymethyl chitosan as a pH-responsive encapsulation and delivery strategy

Preparation, characterization and drug release properties of pH sensitive Zingiber officinale polysaccharide hydrogel beads

The aim of this study was to prepare a drug carrier that could deliver oral insulin to the intestine. A hydrogel beads composed of sodium carboxymethyl cellulose (CMC), Zingiber offtcinale polysaccharide (ZOP) and chitosan (CS) were prepared by ionic gel method as insulin carrier. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and thermogravimetric (TGA) showed that the hydrogel was formed by metal ion coordination between ZOP and CMC and Fe3+, and CS was coated on the surface of the hydrogel ball in the form of non covalent bond. The results showed that the swelling process of hydrogel spheres has significant pH sensitivity. In addition, the hydrogel beads successfully coated insulin, and the drug loading rate (DL) of (ZOP/CMC-Fe3+)@CS could reach 69.43 ± 7.32 mg/g, and the entrapment efficiency (EE) could reach 66.94 ± 7.43 %. In vitro release experiments, the release rate of (CMC/ZOP-Fe3+)@CS in simulated gastric fluid (SGF) for 2 h was <20 %, and the cumulative release rate of insulin after 9 h in simulated intestinal fluid (SIF) reached over 90 %. The results showed that the hydrogel beads prepared in this work could be used as a potential carrier for delivering oral insulin.

An injectable carboxymethyl chitosan hydrogel scaffold formed via coordination bond for antibacterial and osteogenesis in osteomyelitis

The intricate, hostile, and diverse nature of osteomyelitis (OM) poses a challenge for complete bacterial eradication and osteogenesis promotion via conventional treatment. Recently, functional hydrogels exhibiting antibacterial and osteogenic properties emerge as a promising avenue for OM wound healing in clinical practice. However, the preparation procedures and associated costs on cytokine and cell therapies for certain functional hydrogels can be complex and prohibitively expensive. In our research, a hybrid hydrogel dressing has been formulated utilizing carboxymethyl chitosan (CMCS) as the base material, and designed with inherent antibacterial, adhesion, proliferation, and differentiation characteristics, showing promise as a candidate for eradicating infection and promoting bone regeneration. The hybrid hydrogel is composed of interconnected networks of Fe3+-induced self-assembled CMCS and the antibacterial drug ciprofloxacin (CIP), resulting in excellent injectability and moldability. Notably, the CMCS/Fe3+/CIP hybrid hydrogel is capable of regulating antibacterial responses and stimulating osteogenesis in infected microenvironments without additional additives. This injectable antibacterial and osteogenic-promoting hydrogel establish a high-potential platform for low-cost, safe and effective treatment of OM by expediting the initial stages of infected bone wound repair.

Solvent-less carboxymethylation-induced electrostatic crosslinking of chitosan

The successful N-carboxymethylation and concomitant crosslinking of solid chitosan upon heating its mixture with solid monochloroacetic acid, without the use of solvents or catalysts, is reported. The N-carboxymethylation was confirmed through the analysis of the partially depolymerized product using NMR spectroscopy, as well as a control reaction with lysine. This transformation was facilitated by the nucleophilic nature of the free amine group in the repeating unit of chitosan, which possesses lone pair of electrons capable of attacking the carbon center bearing the leaving group and displacing the leaving group in a concerted manner. The crosslinking, on the other hand, was established by the observed insolubility in aqueous acidic solutions, even when subjected to prolonged heating at 60 °C. This crosslinking occurs due to the electrostatic interactions between the carboxylate groups and the adjacent ammonium groups, as supported by evidence from FTIR spectroscopy and a control reaction involving ethyl chloroacetate. The resulting crosslinked carboxymethyl chitosan demonstrated its usefulness in the adsorption of methyl orange and fluorescein, as well as functioning as an organic catalyst for aza-Michael addition, Hantzsch reaction, and substituted perimidine synthesis.

Stimuli-responsive electrospun nanofibers for drug delivery, cancer therapy, wound dressing, and tissue engineering

The stimuli-responsive nanofibers prepared by electrospinning have become an ideal stimuli-responsive material due to their large specific surface area and porosity, which can respond extremely quickly to external environmental incitement. As an intelligent drug delivery platform, stimuli-responsive nanofibers can efficiently load drugs and then be stimulated by specific conditions (light, temperature, magnetic field, ultrasound, pH or ROS, etc.) to achieve slow, on-demand or targeted release, showing great potential in areas such as drug delivery, tumor therapy, wound dressing, and tissue engineering. Therefore, this paper reviews the recent trends of stimuli-responsive electrospun nanofibers as intelligent drug delivery platforms in the field of biomedicine.

Heterogeneity Regulation of Bilayer Polysaccharide Hydrogels for Integrating pH- and Humidity-Responsive Actuators and Sensors

Bilayer hydrogel-based actuators have attracted much interest because inhomogeneous structures are easily constructed in hydrogels. We used three kinds of polysaccharides, including anionic carboxymethyl cellulose (CMC), cationic chitosan (CS), and amphoteric carboxymethyl chitosan (CMCS), as both structure-constructing units and actuation-controlling units in this work to fabricate physically crosslinked poly(vinyl alcohol) bilayer hydrogels. The spatial heterogeneity was tuned by changing the types and concentrations of polysaccharides in different layers, to regulate pH- and humidity-driven actions of bilayer hydrogels. Based on the distortion of the ionic channel during the humidity-motivated deformation of bilayer hydrogels, a two-in-one flexible device integrating a humidity-driven actuator and humidity-responsive sensor was then developed, which could detect the alterations of environmental humidity in real time. Moreover, good tensile toughness and interfacial bonding as well as the strain-resistance effect endowed the bilayer hydrogels with the capability of identifying human motion as a strain sensor, unlocking more application scenarios. This work provides an overall insight into the heterogeneity regulation of bilayer hydrogels using polysaccharides as stimulus-responsive units and also proposes an interesting strategy of manufacturing hydrogel-based flexible devices with both actuating and sensing capabilities.

Structural characterization, stability, and cytocompatibility study of chitosan BaTiO3@ZnO:Er heterostructures

New imaging agents are required in cancer diagnosis to enhance the diagnostic accuracy, classification, and therapeutic management of tumors. Nanomaterials have emerged as a promising alternative to developing new nanostructures with imaging applications. In this study, a heterostructure based on barium titanate (BT), zinc oxide (ZnO), and erbium (Er) was prepared and coated with Chitosan (CS) to investigate their stability and compatibility with biological systems. The structure, particle morphology, luminescence properties, stability, and cytotoxicity of different nanoparticles (NPs) were assessed. The results demonstrated the formation of a [BT@ZnO:Er]-CS heterostructure, which is consistent with the relative intensities and positions of peaks in the X-ray diffraction (XRD) with an average crystallite size of ~76 nm. The electrokinetic measurement results indicate that the coated NPs are the most stable and have an average size close to 200 nm when the pH is between 3 and 5. Finally, we presented a cytotoxicity study of naked and CS-coated NPs. The results indicate that naked NPs exhibit varying cellular toxicity, as indicated by decreased cell viability, morphological changes, and an increase in an apoptotic marker. The CS-coated NPs prevented the cytotoxic effect of the naked NPs, demonstrating the significance of CS as a stabilizing agent.

Microencapsulation of Capsaicin in Chitosan Microcapsules: Characterization, Release Behavior, and Pesticidal Properties against Tribolium castaneum (Herbst)

Capsaicin is a capsaicinoid in hot chili peppers, with excellent antibacterial and antimicrobial activities and a good safety profile, but its poor solubility and instability restrict its effectiveness. This limitation may be mitigated by encapsulation. Herein, capsaicin microcapsules (CCMs) were prepared through layer-by-layer self-assembly, using chitosan and carboxymethyl chitosan as shell materials. The chemical and microstructure structural characterization was evaluated by the methods of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The SEM indicated the microcapsules were irregular in shape with an average size of about 100 μm. The encapsulation had a high loading efficiency of 64.31%. FTIR and XRD revealed the absence of the interaction between the core and shell materials and the amorphous nature of the CCMs. The analysis results of the microcapsules' release behavior showed the burst release of capsaicin in 7 days and a slow progression afterward in three solutions, with the highest release properties in a basic solution, followed by acidic and neutral salt solutions. The entomotoxicity of CCMs was conducted against Tribolium castaneum (Herbst), and its efficacy was compared with pure capsaicin. The CCMs were found to be highly effective against this pest. The LC₅₀ value for capsaicin and its microcapsules was 31.37 and 29.75 mg/kg on adults, respectively. According to these values, T. castaneum's development and reproduction were significantly inhibited compared with the control group. The excellent physicochemical characteristics and insecticidal performance show a high application value for integrated pest control.

An Overview of Coacervates: The Special Disperse State of Amphiphilic and Polymeric Materials in Solution

Individual amphiphiles, polymers, and colloidal dispersions influenced by temperature, pH, and environmental conditions or interactions between their oppositely charged pairs in solvent medium often produce solvent-rich and solvent-poor phases in the system. The solvent-poor denser phase found either on the top or the bottom of the system is called coacervate. Coacervates have immense applications in various technological fields. This review comprises a concise introduction, focusing on the types of coacervates, and the influence of different factors in their formation, structures, and stability. In addition, their physicochemical properties, thermodynamics of formation, and uses and multifarious applications are also concisely presented and discussed.

Coacervates: recent developments as nanostructure delivery platforms for therapeutic biomolecules

Coacervation is a liquid-liquid phase separation that can occur in solutions of macromolecules through self-assembly or electrostatic interactions. Recently, coacervates composed of biocompatible macromolecules have been actively investigated as nanostructure platforms to encapsulate and deliver biomolecules such as proteins, RNAs, and DNAs. One particular advantage of coacervates is that they are derived from aqueous solutions, unlike other nanoparticle delivery systems that often require organic solvents. In addition, coacervates achieve high loading while maintaining the viability of the cargo material. Here, we review recent developments in the applications of coacervates and their limitations in the delivery of therapeutic biomolecules. Important factors for coacervation include molecular structures of the polyelectrolytes, mixing ratio, the concentration of polyelectrolytes, and reaction conditions such as ionic strength, pH, and temperature. Various compositions of coacervates have been shown to deliver biomolecules in vitro and in vivo with encouraging activities. However, major hurdles remain for the systemic route of administration other than topical or local delivery. The scale-up of manufacturing methods suitable for preclinical and clinical evaluations remains to be addressed. We conclude with a few research directions to overcome current challenges, which may lead to successful translation into the clinic.

Facile synthesis of pH-responsive sodium alginate/carboxymethyl chitosan hydrogel beads promoted by hydrogen bond

In this work, a novel synthesis strategy of sodium alginate/carboxymethyl chitosan hydrogel beads promoted by hydrogen bond was described. The beads were prepared by dropping the blends of two polymers into the citric acid solution. Besides hydrogen bonding, electrostatic interactions were also involved in the formation of the hydrogel beads. The thermal stability experiments revealed that the more the content of carboxymethyl chitosan, the better the thermal stability of the beads. The beads exhibited excellent pH sensitivity, pH reversibility, and lactoferrin loading capacity. The swelling ratio of the bead and its protein releasing profile was pH-dependent, which could prevent premature protein release in the gastric environment. Also, the circular dichroism results demonstrated that lactoferrin could maintain its structure during the loading and releasing process. The obtained results revealed that the hydrogel beads prepared in this work could be used as a potential protein carrier for oral delivery.