Sizing up the Next Generation of Nanomedicines

During the past two decades the nanomedicine field has experienced significant progress. To date, over sixty nanoparticle (NP) formulations have been approved in the US and EU while many others are in clinical or preclinical development, indicating a concerted effort to translate promising bench research to commercially viable pharmaceutical products. The use of NPs as novel drug delivery systems, for example, can improve drug safety and efficacy profiles and enable access to intracellular domains of diseased cells, thus paving the way to previously intractable biological targets. However, the measurement of their physicochemical properties presents substantial challenges relative to conventional injectable formulations. In this perspective, we focus exclusively on particle size, a core property and critical quality attribute of nanomedicines. We present an overview of relevant state-of-the-art technologies for particle sizing, highlighting the main parameters that can influence the selection of techniques suitable for a specific size range or material. We consider the increasing need, and associated challenge, to measure size in physiologically relevant media. We detail the importance of standards, key to validate any measurement, and the need for suitable reference materials for processes used to characterize novel and complex NPs. This perspective highlights issues critical to achieve compliance with regulatory guidelines and to support research and manufacturing quality control.