3.2.4. Chemical Composition

NPs chemistry is another fundamental factor contributing to cell interactions. Regarding particle chemistry, Gri ffitt et al. [73] observed di fferent toxicity in zebrafish, daphnids, and algae species for silver and copper NPs with respect to titanium oxide, which resulted in no toxicity problems.

In addition to these characteristic properties of NPs, their state of aggregation must also be taken into account. Aggregation depends on the surface load, material type, and size, among other factors. It has been shown that higher NP concentrations result in higher aggregation and, consequently, lower toxicity [74]. Accordingly, macrophages remove large particles more e fficiently and easily than small ones, which evade this defense mechanism more easily [75].
