Fig. 2. Biological factors affect the evolution of the PC, especially the conformation and orientation of PC-associated proteins. During the journey of NPs in vivo, depending on their route of administration and the overall condition of the body (normal/pathogenic), NPs interact with different types of proteins of different sizes and concentrations. Variations in environmental parameters such as pH, ionic strength, temperature, and shear flow also affect PC structure as NPs travel in vivo.