drug delivery system 73 Article 47 human 39 controlled study 37 Drug Delivery Systems 34 chemistry 32 Humans 28 nonhuman 28 Animals 23 Nanoparticles 23 animal 22 particle size 21 drug release 20 nanoparticle 20 drug formulation 19 procedures 18 in vitro study 17 Targeted drug delivery 15 animal experiment 15 unclassified drug 15 Controlled drug delivery 14 mouse 14 priority journal 14 metabolism 13 pH 13 chitosan 12 drug effect 12 nanocarrier 12 Particle Size 11 drug carrier 11