The green and stable dissolving system based on KOH/urea for homogeneous chemical modification of chitosan

Sequential deacetylation/self-gelling chitin hydrogels and scaffolds functionalized with fucoidan for enhanced BMP-2 loading and sustained release

Bone morphogenetic protein 2 (BMP-2) is a potent osteoinductive factor that promotes bone formation. A major obstacle to the clinical application of BMP-2 is its inherent instability and complications caused by its rapid release from implants. Chitin based materials have excellent biocompatibility and mechanical properties, making them ideal for bone tissue engineering applications. In this study, a simple and easy method was developed to spontaneously form deacetylated β-chitin (DAC-β-chitin) gels at room temperature through a sequential deacetylation/self-gelation process. The structural transformation of β-chitin to DAC-β-chitin leads to the formation of self-gelling DAC-β-chitin, from which hydrogels and scaffolds were prepared. Gelatin (GLT) accelerated the self-gelation of DAC-β-chitin and increased the pore size and porosity of the DAC-β-chitin scaffold. The DAC-β-chitin scaffolds were then functionalized with a BMP-2-binding sulfate polysaccharide, fucoidan (FD). Compared with β-chitin scaffolds, FD-functionalized DAC-β-chitin scaffolds showed higher BMP-2 loading capacity and more sustainable release of BMP-2, and thus had better osteogenic activity for bone regeneration.

The role of urea on the dissolution of starch in NaOH-urea aqueous solutions

Potato starch can be dissolved in NaOH-urea aqueous solutions to form a stable and homogeneous mixture to initiate further modification. The mechanism for the formation of such a solution was investigated by examining the interactions between urea and starch, using rheological tests, ¹³C NMR, FTIR, and a novel Kamlet-Taft solvation parameter analysis. It was found that the optimized dissolution condition was in aqueous 10% w/w NaOH-14% w/w urea, under which 97.4% light transmission was achieved. This was due to dispersive forces between urea and starch without the presence of strong hydrogen bond based interactions. DSC results further showed that the subtle dissolving facilitation of urea might be attributed to the heat released during urea hydrate formation. Compared with conventional hydrothermal gelatinized starch, the starch-NaOH-urea aqueous dispersion exhibited better stability. This highlighted the role of urea in forming a 'bridge' to combine starch with water molecules. This reduces the tendency for starch aggregation via its hydrophobic components. Intrinsic viscosity and GPC analysis indicated that the degradation of starch molecules was significantly reduced. This work provides new insights into the role of urea in starch-NaOH-urea aqueous dispersion. This type of starch solvent formulation will have significant potential for further preparation of starch-based materials for various applications.

Stimuli-Responsive Polysaccharide Hydrogels and Their Composites for Wound Healing Applications

There is a growing concern about wound care, since traditional dressings such as bandages and sutures can no longer meet existing needs. To address the demanding requirements, naturally occurring polymers have been extensively exploited for use in modern wound management. Polysaccharides, being the most abundant biopolymers, have some distinct characteristics, including biocompatibility and biodegradability, which render them ideal candidates for wound healing applications. Combining them with inorganic and organic moieties can produce effective multifunctional composites with the desired mechanical properties, high wound healing efficiencies and excellent antibacterial behavior. Recent research endeavors focus on the development of stimuli-responsive polysaccharide composites for biomedical applications. Polysaccharide composites, being sensitive to the local environment, such as changes of the solution temperature, pH, etc., can sense and react to the wound conditions, thus promoting an effective interaction with the wound. This review highlights the recent advances in stimuli-responsive polysaccharide hydrogels and their composites for use in wound healing applications. The synthetic approaches, physical, chemical, and biochemical properties as well as their function in wound healing will be discussed.

Diabetes immunity-modulated multifunctional hydrogel with cascade enzyme catalytic activity for bacterial wound treatment

Diabetes immunity-modulated wound treatment in response to the varied microenvironments at different stages remains an urgent challenge. Herein, glucose oxidase (GOx) and quasi-amorphous Fe₂O₃ are co-incorporated into Zn-MOF nanoparticle (F-GZ) for cascade enzyme catalytic activities, where not only the high blood glucose in the wound is consumed via the GOx catalysis, but also the effective anti-bacteria is achieved via the degradedly released Zn²⁺ synergistically with the catalytically produced ·OH during the bacterial infection period with the low pH microenvironment. Simultaneously, the reactive oxygen species scavenging and hypoxia relief is realized via catalyzing H₂O₂ to produce O₂ at the relatively elevated pH environment during the wound recovery period. Subsequently, a multifunctional hydrogel with injectable, self-healing and hemostasis abilities, as well as uniformed F-GZ loading is prepared via the copolymerization reaction. This hydrogel behaves as F-GZ but reduces the toxic effects, which thus accelerates the diabetic wound healing. More importantly, this hydrogel is found to modulate the diabetes immunity possibly mediated via the released Zn²⁺, which thus contributes to the recovered pancreatic islet functions with improved glucose tolerance and increased insulin secretion for enhanced diabetic wound treatments. This work initiates a new strategy for simultaneous diabetic wound management and also suggests a potential way for diabetic immunity modulation.

Nature-Derived Okra Gel as Strong Hemostatic Bioadhesive in Human Blood, Liver, and Heart Trauma of Rabbits and Dogs

Bioadhesive performance can be compromised due to bleeding. Bleeding increases mortality. Adhesives with hemostatic function are of great significance. A sustainable and robust hemostatic bioadhesive from okra is reported. The adhesive strength reaches around three and six-fold higher than commercial fibrin on pigskin and glass, respectively. The okra gel presents high-pressure resistance and great underwater adhesive strength. In human blood experiments, the okra gel can activate platelets, enhance the adhesion of activated platelets, and release coagulation factors XI and XII. By forming a fast gel layer and closely adhering to the wound, it can quickly stop bleeding in the liver and heart of rabbits and dogs. Meanwhile, okra gel can cause platelet activation at the wound site and further strengthen its hemostatic performance. It is biocompatible, biodegradable, and can promote wound healing and shows potential as a sustainable bioadhesive, especially in the scenario of significant hemorrhage.

A 4arm-PEG macromolecule crosslinked chitosan hydrogels as antibacterial wound dressing

In order to develop better wound dressings, a novel chitosan hydrogel (Cn-Nm gel) was designed and fabricated by using aldehyde-4-arm polyethylene glycol (4r-PEG-CHO) to crosslink the chitosan dissolved in alkaline solution, amino-4-arm polyethylene glycol (4r-PEG-NH₂) was chosen as the additive simultaneously. The special dissolution technique and macromolecular crosslinking structure endows the Cn-Nm gels with better performance than that of gels prepared by acid dissolving method with micromolecule crosslinker. First, Cn-Nm gels own strong toughness with 500 kPa tensile strength and 1000% elongation, about 400% swelling ratio and fast water absorption rate. Second, about 300 kPa adhesive strength and strippability between the gels and skin is achieved. More importantly, Cn-Nm gels show nearly 100% antibacterial rate towards Escherichia coli and Staphylococcus aureus. Excellent biocompatibility is also proved by the mouse fibroblasts tests. All of the performance makes this developed chitosan-based gel be the potential candidate as a wound dressing.

Homogeneous deacetylation and degradation of chitin in NaOH/urea dissolution system

Since being discovered, alkali/urea has been widely used in the dissolution of natural polysaccharides and the preparation of functional materials such as hydrogels, fibers, films and nanoparticles. This work will focus on verifying the structural stability, homogeneous degradation and deacetylation of chitin in alkali-soluble systems. The chitin was dissolved in NaOH/urea solution and stored at different temperature. At the specific time, the structure, viscosity, acetylation degree (DA) and biocompatibility of chitin and prepared chitosan were determined. The results indicated that dissolution process did not affect the structure and bioactivity of chitin. However, with the increase of storage time and temperature, chitin undergone significant homogeneous deacetylation (DA from 99.5% to 33.2%) and degradation (viscosity from 9284 cP to 1538 cP), accompanying by changes in crystalline structure and thermal stability. Moreover, the processed chitins were no-toxic for the biomedicine applications. This work will provide new ideas for the application of alkali-soluble systems.

A composite sponge based on alkylated chitosan and diatom-biosilica for rapid hemostasis

Rapid control of bleeding is of great significance in military trauma and traffic accidents. In this study, alkylated chitosan (AC) and diatom biosilica (DB) were combined to develop a safe and effective hemostatic composite sponge (AC-DB sponge) for hemorrhage control. Due to the procoagulant chemical structure of AC-DB sponge, it exhibited rapid hemostatic ability in vitro (clotting time was shortened by 78% than that of control group), with favorable biocompatibility (hemolysis ratio < 5%, no cytotoxicity). The strong interface effect between AC-DB sponge and blood induced the erythrocyte and platelets activation, deformation and aggregation, intrinsic coagulation pathway activation, resulting in significant coagulation acceleration. AC-DB sponge had excellent performance in in vivo assessments with shortest clotting time (106.2 s) and minimal blood loss (328.5 mg). All above results proved that AC-DB sponge had great potential to be a safe and rapid hemostatic material.

Green Fabrication of Chitin/Chitosan Composite Hydrogels and Their Potential Applications

Chitin is the second most abundant natural polysaccharide with biocompatibility and bioactivity. Aqueous KOH/urea solution is reported for rapid dissolution of chitin, therefore providing a greener and more efficient avenue to fabricate chitin-based functional materials. Chitosan is the most important derivative of chitin with the acetylation degree lower than 60%. Herein, novel chitin/chitosan composite hydrogels are fabricated from the green and highly efficient KOH/urea aqueous system for the first time. Both chitin and chitosan are dissolved in aqueous KOH/urea solutions, then cross-linked by epichlorohydrin to form bulk chitin/chitosan composite hydrogels (CCGEL). The structural, thermal, mechanical, and swelling properties of CCGEL are thoroughly studied. The cell studies show that NIH-3T3 cells self-assemble to form regular 3D multicellular spheroids on the CCGEL samples with high viability. L929 cells proliferate and intend to form cell aggregates, and the size of the cell aggregates becomes greater with the increase of chitosan loading. Additionally, the CCGEL samples exhibit antibacterial activities. Thus, this pioneering work has provided crucial information for novel chitin/chitosan composite materials constructed via the direct dissolution of chitin and chitosan in aqueous KOH/urea solutions, and presented their potential applications in the cell culture and antibacterial fields.

Marine waste to a functional biomaterial: Green facile synthesis of modified-β-chitin from Uroteuthis duvauceli pens (gladius)

Chitin is the second most abundant biomass on earth but exploited the least. In this study, wastes from Uroteuthis duvauceli was utilized to extract 38.79 ± 1.38% dry weight of β-chitin using a new combination of decolorization, demineralization, and deproteinization processes. β-chitin was then derivatized with acrylamide in an efficient and green aqueous 8 wt% NaOH/4 wt% urea solvent via one-pot etherification. The success of carbamoylethyl ether of chitin and carboxyethyl chitin synthesis was confirmed by FTIR, ¹H NMR, ¹³C NMR, XRD, SEM, TGA, and DSC. The synthesized acrylamide-modified β-chitin derivatives were shown to exhibit water solubility and lower decomposition temperatures, which are primarily due to the disruption of the crystalline structure of β-chitin upon its dissolution and modification. In this era of climate change, this desirable strategy of harnessing β-chitin from wastes and converting it to value-added products is highly sought to mitigate the continuing ecological and economical imbalance brought about by marine-food wastes. To the best of our knowledge, this novel contribution is the first to report biorefinery of squid pens from this particular species and functionalizing it with acrylamide in a facile manner, thus, offering greater potential for future development to biocompatible chitin-based biomaterials intended for industrial, pharmaceutical and biomedical applications.