Fig. 6

Conceptual understanding of the inter-relationships between the 5Bs and the working definitions of these terms as used in this section. Bioavailability indicates the amount of the applied dose that is in the right form to enter the organism, which for NPs depends on the dispersion conditions and the interplay between the medium components and the NP surface. Biopersistence provides an indication of how long the NPs remain in circulation and/or are retained by the organs to which they biodistribute (i.e. the retention half-life) as determined by their adsorbed biomolecule corona. Retention is affected by bioprocessing, which we define as the physicochemical transformation of the NPs by cells or organisms, which are often driven by the acquired biomolecules. Bioprocessing reflects the fact that NPs and their degradation products may impact on the biochemical functioning of the cell or organism, including assimilation into cellular reactions. Finally, bioclearance describes the elimination pathways by which organisms remove NPs, which are dependent upon the uptake route and the biodistribution pattern as different organs have different clearance mechanisms available, as well as the bioprocessing following localisation to the target organs.