"Smart" Polymer Nanogels as Pharmaceutical Carriers: A Versatile Platform for Programmed Delivery and Diagnostics.

"Smart" polymeric nanoformulations are evolving as a promising therapeutic, diagnostic paradigm. The polymeric nanovehicles demonstrated excellent capability to encapsulate theranostic cargos and their successful delivery in physiological conditions and even to monitor the therapeutic response. Currently, polymer nanogels (NGs) are established as capable carriers toward triggered delivery of diverse therapeutic and diagnostic agents. Notably, biodegradable and "intelligent" NGs constructed from intelligent polymers are highly beneficial because of their responsiveness toward endogenous as well as exogenous stimuli like pH gradients, bioresponsiveness, photoresponsiveness, temperature, and so on. In the past decade, plenty of multifunctional NGs with excellent targetability and sensitivity were reported for a wide range of theragnostic applications. This mini-review briefly propounds the synthesis strategies of "smart" NGs and summarizes the notable applications like delivery of genetic materials, anticancer agents, photodynamic/photothermal therapies, imaging, and biosensing. Herein, we have also addressed the current clinical status of NGs and the major challenges that are essential to overcome for the further advancement of NGs for specific applications.