**4. Techniques used in the Physicochemical Characterisations of NCM**

The characterization approaches for NCM are a combination of techniques used to determine crystallinity, particle size, particle size distribution, as well as intra- and intermolecular interactions. In addition, beneficial characterization of NCM with regard to chemical composition is often required. Broadly, the characterization of NCM, much like any other nanometric drug delivery systems, can be classified into in vitro and in vivo categories [66].

To understand the potential performance of NCM in vivo, physicochemical characterisations need to be carried out, followed by cell-culture studies. The physicochemical characterisations offer an understanding of how the NCM will perform prior to cell testing [67]. These are often conducted "in-glass". Cellular testing is less ethically ambiguous, is easier to control and reproduce, and is less expensive when compared to animal testing [68]. Once a proof of concept for NCM has been demonstrated in vitro, safety and therapeutic efficacy are then tested in animal models. The results of animal studies play a fundamental role in decision-making with regard to progression towards clinical trials. An animal model that reflects the pathophysiology of human disease is invaluable when predicting therapeutic outcomes in humans [66,69].

A collection of recommendations pertaining to nanomaterial characterization reviewed a consensus on a large number of nanomaterial properties [67]. A condensed list of physicochemical parameters for the risk assessment of nanomaterials was compiled based on this collection and we concluded that the nanomaterial properties that are listed in at least half of the 28 sources analysed were [67];


In this review, we will use this list to correlate characterization procedures to the properties on the list.
