Chitosan Schiff-Base Hydrogels—A Critical Perspective Review

Abstract

Chitosan is quite a unique polysaccharide due to the presence of the amine groups naturally occurring in its structure. This feature renders it into a polycation which makes it appealing for preparing polyelectrolyte complexes or imine bonds gels. Therefore, the vast majority of hydrogels prepared using Schiff base chemistry have chitosan as one component. Usually, the counterpart is a low molecular weight aldehyde or a macromolecular periodate-oxidized polysaccharide, i.e., cellulose, pullulan, starch, alginate, hyaluronic acid, etc. Indisputable advantages of hydrogels include their quick gelation, no need for crosslinking agents, and self-healing and injectability properties. This gives grounds for further research, both fundamental in materials science and applicative in various domains. This article is a critical assessment of the most relevant aspects of this topic. It also provides a short review of some of the most interesting research reported in the literature supporting the main observations of this perspective.

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

“…It is well documented in the literature that hydrogels are easily formed by the reaction of CS with dialdehyde derivatives via the rapid formation of Schiff base bonds [55,56].…”

“…It is well documented in the literature that hydrogels are easily formed by the reaction of CS with dialdehyde derivatives via the rapid formation of Schiff base bonds [55,56]. Therefore, the oxidized pullulan (OP) with a degree of oxidation of 43%, which corresponds to the 5.26 mmol/g aldehyde groups' content, and a Mw of 7000 g/mol, was synthesized by using NaIO 4 as the oxidizing agent [55] and was used both as cross-linker and network polymeric component.…”

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

“…This reaction is pH-sensitive, mild, and biocompatible [46]. Due to its reversible property, it enhances the stability of hydrogel networks and provides self-healing properties, making them suitable for the injection and delivery of living cells and drugs in situ [117,118]. Chen et al developed an injectable hydrogel system based on the Schiff base reaction for meniscus repair [37].…”

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

“…However, chemical cross-linking can be used in addition to freezing for a better stability of the matrix [21,24,26]. To avoid the low molecular cross-linker agents that are usually toxic [27], polymers with functional moieties such as aldehyde groups can be used as macromolecular cross-linkers [28]. Different oxidized polysaccharides can be used for this purpose, including oxidized pullulan (OP) [28,29]; its oxidation leads to the desired aldehyde content [30] and it has been proved to interact with CS via the Schiff base reaction [29,31,32].…”

“…To avoid the low molecular cross-linker agents that are usually toxic [27], polymers with functional moieties such as aldehyde groups can be used as macromolecular cross-linkers [28]. Different oxidized polysaccharides can be used for this purpose, including oxidized pullulan (OP) [28,29]; its oxidation leads to the desired aldehyde content [30] and it has been proved to interact with CS via the Schiff base reaction [29,31,32]. In addition, pullulan is a microbial-produced biopolymer used in biomedical applications due to its non-immunogenic, non-carcinogenic, and non-mutagenic nature [33].…”