Credit: © 2007 Elsevier

For nanomaterials to be truly useful in medicine, understanding their biodistribution — how and where the materials travel and accumulate — in living systems is essential. Analysing this property requires both careful characterization of the materials and a good animal model with appropriate sample size and robust statistical analyses, yet few studies have achieved this. Now, a group of biologists, oncologists and statisticians in the US show that gold-dendrimer nanocomposites enter different organs in mice depending on their charge and size.

Mohamed Khan and colleagues1 synthesized, characterized and injected five types of Au-dendrimer composites — with particle sizes ranging from 5 to 22 nm and either positive, negative or neural surface charges — into mice. The various organs, blood and excrements of the treatment groups were analysed for gold at various time points and compared. Size and charge of the materials affected biodistribution and excretion, with the smallest positive particles accumulating in the kidneys and larger ones going to the spleen, liver, lungs and heart.

In the absence of molecules that specifically target the particles to a particular region in the body, this selective accumulation in the organs suggests that size and charge are important considerations when designing future nanomaterials for medical applications. Moreover, the team emphasized that interactions of nanomaterials with living systems should be studied empirically and not rely on extrapolations from previous studies.