Nanoparticles (NPs) have been found to be potential targeted and controlled release drug delivery systems. Various drugs can be loaded in the NPs to achieve targeted delivery. Chitosan NPs being biodegradable, biocompatible, less toxic and easy to prepare, are an effective and potential tool for drug delivery. Chitosan is natural biopolymer which can be easily functionalized to obtain the desired targeted results and is also approved by GRAS (Generally Recognized as Safe by the United States Food and Drug Administration [US FDA]). Various methods for preparation of chitosan NPs include, ionic cross-linking, covalent cross-linking, reverse micellar method, precipitation and emulsion-droplet coalescence method. Chitosan NPs are found to have plethora of applications in drug delivery diagnosis and other biological applications. The key applications include ocular drug delivery, per-oral delivery, pulmonary drug delivery, nasal drug delivery, mucosal drug delivery, gene delivery, buccal drug delivery, vaccine delivery, vaginal drug delivery and cancer therapy. The present review describes the formation of chitosan, synthesis of chitosan NPs and their various applications in drug delivery.

Transdermal delivery over the past decade has become the field of interest for drug delivery due to its various advantages such as no first-pass metabolism, increased drug bioavailability, and easy administration. Different vesicle systems like ethosomes, liposomes, niosomes, and transferosomes along with particle systems like lipid nanoparticles, polymeric nanoparticles, carbon nanotubes, and fullerenes have been developed. These vesicles and particle systems have been developed using various easy and effective methods like cold injection method, rotary film evaporation, thin film hydration, high shear homogenization, solvent extraction method, and many more. These drug delivery systems are a very effective and feasible option for transdermal drug delivery and further developments can be made to increase their use. This article explains in detail the preparation methods and applications for these drug delivery systems.

Fungal infection remains a significant therapeutic concern owing to the scarcity of drugs, resistance development, and high levels of toxicity of many conventional antifungals. In this regard, chitosan is one such natural polymer whose biocompatibility, biodegradability, and antimicrobial nature have made it the focus of scientific interest. However, the main problem lies in the polymer’s limited aqueous solubility under physiological conditions and its poor efficacy against fungi. Thus, quaternary ammonium functionalization represents a convenient approach to solving the problem by introducing permanent positive charges into the molecular structure of chitosan, thereby improving water solubility, enabling membrane interactions, and conferring broad-spectrum antifungal activity. Such derivatives can exhibit strong interactions with the negatively charged surface of fungal cells, compromising membrane integrity and inhibiting biofilm formation. Apart from their antifungal activity, such compounds are also promising in local delivery systems, which include coatings, nanoparticles, hydrogels, and wound dressings. Considering their unique chemistry, such compounds appear quite promising for the development of novel antifungal biomaterials that can be adapted to different clinical and pharmaceutical needs. Overall, quaternary ammonium-modified chitosan could be considered a promising platform for the development of next-generation antifungal agents. This review offers a comprehensive discussion regarding the synthesis, mode of action, formulation advancements, safety profile, potential applications, and future directions of quaternary ammonium-functionalized chitosan derivatives as an antifungal agent, with an emphasis on artificial intelligence contributions to this area of research.