Smart Nanoparticles in Drug/Gene Delivery

New achievements in the realm of nanoscience and innovative advances in nanomedicine have allowed micro/nanoparticles (MNPs) to progress to the point of becoming useful for drug and gene delivery applications. The various differences between the extracellular and intracellular environments of cancerous and normal cells, and the particular characteristics of tumors such as physicochemical properties, neovasculature, elasticity, surface electrical charge, and pH have all motivated the design and fabrication of innovative “smart” MNPs for stimulus-responsive and controlled drug release. These novel MNPs can be tailored to be responsive to variations in pH, redox potential, enzymatic activation, thermal gradients, magnetic fields, light, and ultrasound (US), or can even be responsive to dual or multi-combinations of different stimuli. This unparalleled capability has increased their importance as site-specific controlled drug delivery systems (DDSs) and has encouraged their rapid development in recent years. A deeper understanding of the underlying mechanisms of these DDS approaches is expected to further contribute to this groundbreaking field of nanomedicine. Smart nanocarriers in the form of MNPs that can be triggered by internal or external stimulus are summarized in the present chapter, including pH-sensitive peptides and polymers, redox-responsive micelles and nanogels, thermo- or magnetic-responsive nanoparticles (NPs), mechanical- or electrical-responsive MNPs, and light- or ultrasound-sensitive particles. This chapter highlights some recent advances in smart MNPs according to their activation stimulus (physical, chemical, or biological) and looks forward to future pharmaceutical applications.