Particle Charge and Surface Hydrophobicity of Colloidal Drug Carriers

Abstract

The fate of colloidal particles in the body is determined by different factors such as particle size and shape,1–8 particle charge9–22 and surface hydrophobicity.23–32 Among them, surface hydrophobicity seems to play an important role in particle phagocytosis. Particles with different surface charges will show, after incubation with serum, a similar negative charge9,33,34 of about -11 mV to -18 mV (calculated as the Zeta potential). This is due to the adsorption of serum components which shield the original charge and create a new one. Therefore, for subsequent interactions with macrophages, i.e. clearance by the reticuloendothelial system (RES), the colloidal particles may have similar surface charges but not similar surface hydrophobicity. The repulsive forces between negatively charged macro-phages and the negatively charged particles will thus be normally the same, but due to different van der Waals (hydrophobic) interactions the attractive forces will be of different magnitudes. The size of these attractive forces is proportional to the hydrophobicity of the particle surface layer of blood components (opsonisation).