Nanoparticles in drug delivery: past, present and future.

This opinion paper relates how nanoparticles were discovered in the seventies and how the development of biodegradable materials and nanoparticle surface functionalization has allowed new treatment strategies. The reasons why only very few nanoparticle-based medicines are on the market or in late clinical trials are discussed and some new approaches are identified. Future challenges in the nanoparticle field are also identified.