Entry of nanoparticles into cells and tissues: status and challenges

In this article we discuss how nanoparticles (NPs) of different compositions may interact with and be internalized by cells, and the consequences of that for cellular functions. A large number of NPs are made with the intention to improve cancer treatment, the goal being to increase the fraction of injected drug delivered to the tumor and thereby improve the therapeutic effect and decrease side effects. Thus, we discuss how NPs are delivered to tumors and some challenges related to investigations of biodistribution, pharmacokinetics, and excretion. Finally, we discuss requirements for bringing NPs into clinical use and aspects when it comes to usage of complex and slowly degraded or nondegradable NPs.