Smart nanogels as promising platform for delivery of drug, gene, and vaccine; therapeutic applications and active targeting mechanism

Nanohydrogels, known as nanogels, are three-dimensional networks of cross-linked hydrophilic, natural, or synthetic polymers. The high water content of swollen nanohydrogels, their highly porous structure, and the similarity of their physical and chemical properties to the extracellular matrix give them excellent biocompatibility. Nanogels can be highly advantageous when used as "smart" materials that can detect changes in their environment. As demonstrated by the broad range of research, responsive hydrogels are revolutionizing drug delivery systems and uncovering new advantages capabilities in clinical applications. The physical properties of nanogels are adjusted easily in response to various stimuli such as pH, temperature, light, and ionic strength. By this means, smart hydrogels have found wide applications for therapeutic purposes. Advanced drug and gene delivery systems have been developed to control the time and place of cargo transfer to the target site with minimal side effects. In addition, nanogels play a prominent role in regenerative medicine and tissue engineering, while finding notable applications in spinal cord injury recovery. In this review, the structure of nanogels is briefly discussed and then different factors governing the release rate and targeting mechanism have been discussed. Possible therapeutic applications of different nanogels in cancer, wound healing, and neurological disorders are reviewed and toxicological concerns of nanogels are overlooked.