Self-healing, injectable chitosan-based hydrogels: structure, properties and biological applications

Conventional biomaterials suffer from mechanical stresses and biochemical degradation, compromising performance and structural integrity. Hydrogels are three-dimensional networks that hold a huge quantity of water but can retain their internal structure due to chemical and physical crosslinking. Unlike self-healing injectable hydrogels, they lack the capacity to repair their inherent structure after damage due to the absence of reversible bonds, but these self-healing injectable hydrogels can withstand and reverse damage accumulation. The recoverability of self-healing injectable hydrogels stems from the presence of reversible chemical bonds within their structure. Schiff base linking involves reversible imine or hydrazone bond formation through reactions between aldehydes or ketones, commonly used in chitosan-based hydrogels. Rheological and morphological characterization help determine the precise structure, mechanical strength and bond types. Moreover, the capacity to hold water in hydrogels can closely mimic the extracellular matrix (ECM). Incorporating various polymers and crosslinkers enhances mechanical strength and biocompatibility. Their porous and hydrophilic nature allows for versatile applications, such as loading living cells, drugs, growth factors, and miRNA, promoting cell proliferation and adhesion. The injectability of these hydrogels facilitates precise administration through narrow syringes, enabling rapid local confinement and reducing off-target side effects. Through 3D bioprinting, the injectability can be proven and through experimental studies conducted in vitro using dissolution tests or in vivo on rodents, the sustained drug release capabilities of these hydrogels can be determined. Chitosan-based self-healing injectable hydrogels possess remarkable properties that find applications in tissue-engineered scaffolds, drug delivery, wound dressings, and cancer treatment.