Surface modification of functional nanoparticles for controlled drug delivery

Surface-modified nanoparticles have received much attention as drug carriers. Natural and synthetic polymers are used as the materials to prepare nanoparticles and the properties of these nanoparticles originate with these polymeric materials. In particular, these nanoparticles are modified for specific objectives. The surface characteristics of (shell) nanoparticles are more important than those of the core, because the shell layer directly contacts body fluids and organs. Generally, the nanoparticles are coated with hydrophilic polymer to give long circulation and/or are conjugated with functional ligands or proteins for site-specific delivery. In this review, the preparative methods and the applications of surface modification of polymeric functionalized nanoparticles for long-circulation, site-specific delivery, and oral delivery are discussed.