Liposomes and inorganic nanoparticles for drug delivery and cancer imaging

Recently, there have been several advancements in material sciences and nanosciences. At the moment these new techniques are slowly entering into clinical settings in drug delivery and imaging. In this review, we will look more closely at the applications that are at the forefront of this translation and examine critical aspects that are involved in the process. Nanoparticles have been increasingly used in clinical settings for drug delivery over the past two decades. Lipid-based nanoparticles are front-runners, but other innovative strategies, such as small inorganic nanoparticles, are entering into the field, particularly for imaging applications. Lipid-based nanoparticles can be metabolized and consumed by the body and are regarded as safe for clinical use. They are usually large with hydrodynamic diameters of approximately 100-200 nm; however, phospholipid-containing particles such as microbubbles with diameters as low as 10 microm in size and micelles with diameters of 10-40 nm can also be used. Hollow liposomes with a large aqueous inner cavity can carry high payloads of drugs and imaging moieties, but are easily trapped by liver kupffer cells and can result in lower tissue penetration rates. New classes of particles with hydrodynamic diameters of < 10 nm, which are cleared by the kidneys, have recently been developed. These particles have been used primarily for imaging applications since they offer only small loading capacities for drugs. However, new strategies such as surface-coupled prodrugs have been developed to facilitate drug delivery in small nanoparticles. We describe different strategies for targeted delivery, imaging and controlled release, and discuss the ability of small inorganic particles as well as larger nanoparticles to be used broadly in human diagnostics and drug delivery.