Chitosan Schiff-Base Hydrogels-A Critical Perspective Review

Injectable and self-healing carboxymethyl chitosan/carboxymethyl cellulose/marine snail peptide hydrogel for infected wound healing

Treatment of bacterial infected full-thickness wounds remains a great challenge in clinic. Herein, a HYP hydrogel was prepared using carboxymethyl chitosan, dialdehyde carboxymethyl cellulose, and marine snail peptide (Tyr-Ile-Ala-Glu-Asp-Ala-Glu-Arg) as starting materials. The marine snail peptide with good antioxidant activity could remove the reactive oxygen species in wound sites, thereby alleviating the excessive inflammatory response. The dynamic Schiff-base bonds endowed HYP with good injectable and self-healing abilities. HYP exhibited suitable gelation time, good rheological properties, and unique porosity structure, which were conducive to wound healing. In vitro biological studies indicated that HYP showed good biocompatibility, low hemolysis ratio, and improved antibacterial and antioxidant activities. In vivo study revealed that HYP could promote wound healing in a bacterial infected full-thickness skin defect rat model. The wound tissues showed reduced number of inflammatory cells, newly formed hair follicles, and obvious collagen deposition. The expression of inflammatory and angiogenesis related biomarkers (IL-6, IL-10, CD31, and α-SMA) significantly improved. Therefore, HYP hydrogel showed great application prospect as a wound dressing for bacterial infected wound.

6-Aminocoumarin-derived Schiff base gelators: aggregation and sensing of CN-, Fe3+, Cu2+ and CO2 under different conditions

Herein, we report the synthesis, characterization, supramolecular gelation and multiple applications of 6-aminocoumarin-derived Schiff bases 1 and 2. Both Schiff bases underwent gelation in DMF-H2O (2 : 1, v/v), DMSO-H2O (2 : 1, v/v) and dioxane-H2O (2 : 1, v/v) involving weak forces. Furthermore, the gels were stable and exhibited good viscoelastic properties. The storage modulus (G') of each gel was considerably higher than its loss modulus (G''). The higher value of the crossover point and lower value of tan δ for the gel of Schiff base 2 compared to the gel of Schiff base 1 demonstrated the better gelation behaviour of 2 than that of 1 in DMF-H2O (2 : 1, v/v). Further, iodo-analogue 2 exhibited cross-linked helical morphology, whereas non-iodo analogue 1 exhibited long chain fibrous morphology, as observed via FESEM. These differences in morphology and viscoelastic behaviors were attributed to the iodo group present in 2, which influenced its aggregation involving halogen bonding. To demonstrate their application, the DMF-H2O (2 : 1, v/v) gels of both 1 and 2 recognized CN- over a series of other anions by exhibiting a gel-to-sol phase change. Besides anion sensing, gels 1 and 2 selectively detected Fe3+ and Cu2+ ions over other metal ions via a gel-to-gel colour change. Finally, CN--treated solutions of 1 and 2 allowed the successful detection of CO2 by the naked eye. Moreover, the detection was possible using a test-kit method.

Natural Regenerative Hydrogels for Wound Healing

Regenerative hydrogels from natural polymers have come forth as auspicious materials for use in regenerative medicine, with interest attributed to their intrinsic biodegradability, biocompatibility, and ability to reassemble the extracellular matrix. This review covers the latest advances in regenerative hydrogels used for wound healing, focusing on their chemical composition, cross-linking mechanisms, and functional properties. Key carbohydrate polymers, including alginate, chitosan, hyaluronic acid, and polysaccharide gums, including agarose, carrageenan, and xanthan gum, are discussed in terms of their sources, chemical structures and specific properties suitable for regenerative applications. The review further explores the categorization of hydrogels based on ionic charge, response to physiological stimuli (i.e., pH, temperature) and particularized roles in wound tissue self-healing. Various methods of cross-linking used to enhance the mechanical and biological performance of these hydrogels are also examined. By highlighting recent innovations and ongoing challenges, this article intends to give a detailed understanding of natural hydrogels and their potential to revolutionize regenerative medicine and improve patient healing outcomes.

Chitosan-Alginate Gels for Sorption of Hazardous Materials: The Effect of Chemical Composition and Physical State

Chitosan, alginate, and chitosan-alginate (50:50) mixed hydrogels were prepared by freeze casting, freeze-drying, and subsequent physical cross-linking. Chitosan was cross-linked with citrate and alginate with calcium ions, while the mixed gels were cross-linked with both cross-linking agents. Both cryogels and xerogels were obtained by lyophilization and drying of the hydrogels. We investigated the effect of the chemical composition and the physical state of gels on the gel structure and sorption of model dyes. Alginate and mixed gels cross-linked with Ca2+ ions sorbed 80-95% of cationic dye from the solutions. The chitosan gels are primarily capable of adsorbing anionic dyes, but at near-neutral pH, their capacity is lower than that of alginate gels, showing 50-60% dye sorption. In the case of alginate gels, the dye sorption capacity of xerogels, cryogels, and hydrogels was the same, but for chitosan gels, the hydrogels adsorbed slightly less dye than the dried gels.

Current trend on preparation, characterization and biomedical applications of natural polysaccharide-based nanomaterial reinforcement hydrogels: A review

The tunable properties of hydrogels have led to their widespread use in various biomedical applications such as wound treatment, drug delivery, contact lenses, tissue engineering and 3D bioprinting. Among these applications, natural polysaccharide-based hydrogels, which are fabricated from materials like agarose, alginate, chitosan, hyaluronic acid, cellulose, pectin and chondroitin sulfate, stand out as preferred choices due to their biocompatibility and advantageous fabrication characteristics. Despite the inherent biocompatibility, polysaccharide-based hydrogels on their own tend to be weak in physiochemical and mechanical properties. Therefore, further reinforcement in the hydrogel is necessary to enhance its suitability for specific applications, ensuring optimal performance in diverse settings. Integrating nanomaterials into hydrogels has proven effective in improving the overall network and performance of the hydrogel. This approach also addresses the limitations associated with pure hydrogels. Next, an overview of recent trends in the fabrication and applications of hydrogels was presented. The characterization of hydrogels was further discussed, focusing specifically on the reinforcement achieved with various hydrogel materials used so far. Finally, a few challenges associated with hydrogels by using polysaccharide-based nanomaterial were also presented.

Sustainable food packaging: Harnessing biowaste of Terminalia catappa L. for chitosan-based biodegradable active films for shrimp storage

Shrimp, a globally consumed perishable food, faces rapid deterioration during storage and marketing, causing nutritional and economic losses. With a rising environmental consciousness regarding conventional plastic packaging, consumers seek sustainable options. Utilizing natural waste resources for packaging films strengthens the food industry. In this context, we aim to create chitosan-based active films by incorporating Terminalia catappa L. leaves extract (TCE) to enhance barrier properties and extend shrimp shelf life under refrigeration. Incorporation of TCE improves mechanical, microstructural, UV, and moisture barrier properties of the chitosan film due to cross-linking interactions, resulting in robust, foldable packaging film. Active TCE film exhibits high antioxidant property due to polyphenols. These films also exhibited low wettability and showed hydrophobicity than neat CH films which is essential for meat packaging. These biodegradable films offer an eco-friendly end-of-life option when buried in soil. TCE-loaded films effectively control spoilage organisms, prevent biochemical spoilage, and maintain shrimp freshness compared to neat CH films during refrigerated condition. The active TCE film retains sensory attributes better than neat chitosan, aligning with consumer preference. The developed edible and active film from waste sources might offer sustainable, alternative packaging material with a lower carbon footprint than petroleum-based sources.

Chitosan-Oxidized Pullulan Hydrogels Loaded with Essential Clove Oil: Synthesis, Characterization, Antioxidant and Antimicrobial Properties

Emulsion hydrogels are promising materials for encapsulating and stabilizing high amounts of hydrophobic essential oils in hydrophilic matrices. In this work, clove oil-loaded hydrogels (CS/OP-C) are synthesized by combining covalent and physical cross-linking approaches. First, clove oil (CO) was emulsified and stabilized in a chitosan (CS) solution, which was further hardened by Schiff base covalent cross-linking with oxidized pullulan (OP). Second, the hydrogels were subjected to freeze-thaw cycles and, as a result, the clove oil was stabilized in physically cross-linked polymeric walls. Moreover, due to cryogelation, the obtained hydrogels exhibited sponge-like porous interconnected morphology (160-250 µm). By varying the clove oil content in the starting emulsion and the degree of cross-linking, the hydrogels displayed a high water retention capacity (swelling ratios between 1300 and 2000%), excellent elastic properties with fast shape recovery (20 s) after 70% compression, and controlled in vitro clove oil release in simulated skin conditions for 360 h. Furthermore, the prepared clove oil-loaded hydrogels had a strong scavenging activity of 83% and antibacterial and antifungal properties, showing a bacteriostatic effect after 48 and 72 h against S. aureus and E. coli. Our results recommend the new clove oil-embedded emulsion hydrogels as promising future materials for application as wound dressings.

Advances in Hydrogels for Meniscus Tissue Engineering: A Focus on Biomaterials, Crosslinking, Therapeutic Additives

Meniscus tissue engineering (MTE) has emerged as a promising strategy for meniscus repair and regeneration. As versatile platforms, hydrogels have gained significant attention in this field, as they possess tunable properties that allow them to mimic native extracellular matrices and provide a suitable microenvironment. Additionally, hydrogels can be minimally invasively injected and can be adjusted to match the shape of the implant site. They can conveniently and effectively deliver bioactive additives and demonstrate good compatibility with other functional materials. These inherent qualities have made hydrogel a promising candidate for therapeutic approaches in meniscus repair and regeneration. This article provides a comprehensive review of the advancements made in the research on hydrogel application for meniscus tissue engineering. Firstly, the biomaterials and crosslinking strategies used in the formation of hydrogels are summarized and analyzed. Subsequently, the role of therapeutic additives, including cells, growth factors, and other active products, in facilitating meniscus repair and regeneration is thoroughly discussed. Furthermore, we summarize the key issues for designing hydrogels used in MTE. Finally, we conclude with the current challenges encountered by hydrogel applications and suggest potential solutions for addressing these challenges in the field of MTE. We hope this review provides a resource for researchers and practitioners interested in this field, thereby facilitating the exploration of new design possibilities.

Tri-Component Hydrogel as Template for Nanocrystalline Hydroxyapatite Deposition Using Alternate Soaking Method for Bone Tissue Engineering Applications

Composite hydrogels containing apatite-like particles can act as scaffolds for osteoblast proliferation, with applications in bone tissue engineering. In this respect, porous biocompatible hydrogels were obtained from chitosan, oxidized pullulan, and PVA in different ratios. The stability of the hydrogels was ensured both by covalent bonds between aldehyde groups of oxidized pullulan and free amino groups of chitosan, and by physical bonds formed during freeze-thaw cycles and lyophilization. The deposition of calcium phosphates was performed by alternate soaking of the porous hydrogels into solutions with calcium and phosphate ions, assuring a basic pH required for hydroxyapatite formation. The mineralized hydrogels were characterized using FTIR spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis, showing that inorganic particles containing between 80 and 92% hydroxyapatite were deposited in a high amount on the pore walls of the polymeric matrix. The composition of the organic matrix influenced the crystallization of calcium phosphates and the mechanical properties of the composite hydrogels. In vitro biological tests showed that mineralized hydrogels support the proliferation of MG-63 osteoblast-like cells to a greater extent compared to pristine hydrogels.

Biomass-based single- and double-network hydrogels derived from cellulose microfiber and chitosan for potential application as plant growing substrate

A series of hydrogels were synthesized from renewable and low-cost micro-sized cellulose fiber. The single-network hydrogel was composed of cellulose fiber and a small amount of another polysaccharide, chitosan, which 'glued' individual cellulose fiber pieces together through Schiff-base bonding. The double-network hydrogel was constructed by adding a secondary network, the covalently crosslinked polyacrylamide, into the single-network hydrogel, which was synthesized by conducting Schiff-base reaction and free radical polymerization at the same time in a facile one-pot process. In both single- and double-network hydrogels, cellulose fiber constituted the dominant component. Both types of hydrogels exhibited good swelling properties. The double-network hydrogel showed much improved stability against soaking in water and higher salt tolerance. Germination experiment with choy sum seeds sowed on hydrogel surface showed that the seeds were able to germinate and further develop roots, shoots, and true leaves, demonstrating the potential of the biomass-derived hydrogels for soilless plant growing applications.

Chitosan Sponges with Instantaneous Shape Recovery and Multistrain Antibacterial Activity for Controlled Release of Plant-Derived Polyphenols

Biomass-derived materials with multiple features are seldom reported so far. Herein, new chitosan (CS) sponges with complementary functions for point-of-use healthcare applications were prepared by glutaraldehyde (GA) cross-linking and tested for antibacterial activity, antioxidant properties, and controlled delivery of plant-derived polyphenols. Their structural, morphological, and mechanical properties were thoroughly assessed by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and uniaxial compression measurements, respectively. The main features of sponges were modulated by varying the CS concentration, cross-linking ratio, and gelation conditions (either cryogelation or room-temperature gelation). They exhibited complete water-triggered shape recovery after compression, remarkable antibacterial properties against Gram-positive (Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes)) and Gram-negative (Escherichia coli (E. coli), Salmonella typhimurium (S. typhimurium)) strains, as well as good radical scavenging activity. The release profile of a plant-derived polyphenol, namely curcumin (CCM), was investigated at 37 °C in simulated gastrointestinal media. It was found that CCM release was dependent on the composition and the preparation strategy of sponges. By linearly fitting the CCM kinetic release data from the CS sponges with the Korsmeyer-Peppas kinetic models, a pseudo-Fickian diffusion release mechanism was predicted.