Applications of Ionic Liquids, Poly(Ionic Liquids), Ionic Liquid–Biopolymer Systems, and Their Composites

Dear Colleagues,

Ionic liquids (ILs) are versatile materials with outstanding applications due to their excellent properties, such as low volatility, thermal stability, and chemical durability. They are extremely important in synthesis and catalysis, serving as solvents and catalysts in chemical reactions (organic synthesis, biocatalysis, and polymerizations) owing to their ability to solubilize a wide range of materials, including water-insoluble biopolymers. ILs are also used as electrolytes and antimicrobial agents. They have demonstrated the potential to replace conventional antibiotics in some applications. However, when used improperly, most ILs are toxic to humans and the environment. Therefore, they can lead to significant environmental pollution and various adverse health effects. To address this issue, ILs can be polymerized to produce poly(ionic liquid)s (PILs) or become physically associated with polymeric systems, resulting in composite materials. Polymerization and physical association with biopolymers can significantly reduce the cytotoxicity of ILs, expanding the range of applications for these materials. The reduction in the cytotoxicity of polymerized ILs is due to a decrease in their ionic mobility, an increase in their stability, a molecular structure change, and mainly a decrease in the poly(ionic liquid)’s (PIL) solubility in water, limiting the capacity of PILs to interact with biological systems. PILs are a class of hybrid materials offering a wide range of applications due to their unique properties and versatility. Applications include their use as selective membranes, as raw materials for sensor development, in catalysis, within optoelectronic devices, as biomaterials for controlled drug release, within the tissue engineering of biomaterials, and in thin antimicrobial films.

The physical association of ILs with biopolymers has resulted in cytocompatible, stable, and antimicrobial materials. Biopolymers interact with ILs, reducing their capacity to interact with biological systems. Polysaccharide-based surface coatings containing ILs as additives have shown virucidal activity within 24 hours while maintaining cytocompatibility for fibroblast cells. To achieve antimicrobial and cytocompatibility, the IL concentration in the surface coatings must be modulated, and the polymeric system needs to interact with the IL, especially with the hydrophilic head of the IL, leaving the hydrophobic tail available on the coating surface to interact with the microbial envelope. The interactions between ILs and biopolymers can stabilize the ILs, preventing their leaching into surrounding environments and imparting stability and cytocompatibility. The ILs impart strong biocide action to the resulting composite materials, amplifying the scope of their applications. Furthermore, physical associations between ILs and biopolymers have yielded cytocompatible thin films with outstanding antimicrobial activity against bacteria and viruses. This Special Issue focuses on developing and applying PILs and IL-based systems associated with biopolymers to real-world applications.

Dr. Alessandro Francisco Martins
Guest Editor

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• synthesis
• polymerization
• materials
• hydrogels
• drug delivery systems
• antimicrobial activity
• surface coatings
• films, membranes
• hydrogels
• composites
• technological applications