Stimulus-responsive polymeric nanogels as smart drug delivery systems.

Nanogels are three-dimensional nanoscale networks formed by physically or chemically cross-linking polymers. Nanogels have been explored as drug delivery systems due to their advantageous properties, such as biocompatibility, high stability, tunable particle size, drug loading capacity, and possible modification of the surface for active targeting by attaching ligands that recognize cognate receptors on the target cells or tissues. Nanogels can be designed to be stimulus responsive, and react to internal or external stimuli such as pH, temperature, light and redox, thus resulting in the controlled release of loaded drugs. This "smart" targeting ability prevents drug accumulation in non-target tissues and minimizes the side effects of the drug. This review aims to provide an introduction to nanogels, their preparation methods, and to discuss the design of various stimulus-responsive nanogels that are able to provide controlled drug release in response to particular stimuli. STATEMENT OF SIGNIFICANCE: Smart and stimulus-responsive drug delivery is a rapidly growing area of biomaterial research. The explosive rise in nanotechnology and nanomedicine, has provided a host of nanoparticles and nanovehicles which may bewilder the uninitiated reader. This review will lay out the evidence that polymeric nanogels have an important role to play in the design of innovative drug delivery vehicles that respond to internal and external stimuli such as temperature, pH, redox, and light.