Behaviors and Persistence of Nanomaterials in Biomedical Applications

Chapter 4Interactions of Nanomaterials with Biological Systems

4.1 Cellular Level (in vitro)

4.1.1 Cellular Uptake and Intracellular Fate

Internalization of macromolecules inside cells occurs through endocytosis. However, depending on the size, charge and degree of hydrophobicity, the cellular uptake of nutrients, proteins, signaling factors and other important biomolecules, can follow diverse pathways. This is also true for nanomaterials. The two main routes by which macromolecules and nanomaterials diffuse inside cells from the extracellular milieu are phagocytosis and pinocytosis.

Phagocytic uptake is the main mechanism through which molecules or materials whose size exceeds some hundreds of nm are internalized by cells. Indeed, it is generally accepted that phagocytosis occurs mainly for materials above 500 nm, though some groups have reported phagocytic uptake of smaller nanoparticles [1]. During phagocytosis, nanomaterials in physical contact with cells are engulfed and drawn inward within the cytoplasm through invagination of plasma membrane into vesicles called phagosome. Phagocytosis is a very specific uptake pathway, since it occurs through recognizing binding proteins. It is the main mechanism employed by immune system to provide clearance of pathogens from the body through specialized phagocytic cells, called macrophages, which are capable of engulfing particles even bigger than their own volume.

Pinocytosis is an internalization mechanism that takes place through ...