Macrophage uptake of Janus particles depends upon Janus balance.

Properties of synthetic particles, such as size and shape, influence how immune cells uptake vaccine and drug carriers. Here, we explore the role of a new property, anisotropic presentation of ligands, in particle uptake by macrophage cells. We use micrometer-sized Janus particles that are partially coated with ligands and investigate how the ligand patch size (Janus balance) affects their uptake by macrophages. Macrophage uptake of both 1.6 and 3 μm Janus particles is enhanced as the size of the ligand patch increases. However, presenting ligands asymmetrically reduces particle phagocytosis; Janus particles with the same amount of ligands as uniformly coated particles are internalized less efficiently. We also show that, because of the asymmetric geometry of Janus particles, the onset of ligand-mediated phagocytosis depends upon the orientation of the particles with respect to the cells. This study demonstrates Janus balance as a new parameter that we can use to manipulate the macrophage uptake of particles.