Macrophage Plasticity and Polarization: Relevance to Biomaterials

Diversity and plasticity are hallmarks of mononuclear phagocytes. In response to microenvironmental signals, macrophages may undergo M1 (classical) or M2 (alternative) activation, which represent extremes of a continuum in a spectrum of activation states. In addition to the known properties of macrophage phenotypes in host defense and cancer growth and progression, new perspectives in regenerative medicine have revisited the role of macrophages in tissue repair and host response to implantable biomaterials. Emerging data suggest that implanted biomaterials may actively interact with macrophages and modify their polarization state, thus decisively affecting the functional outcome of the implants. The further clarification of mechanisms and molecules involved in biomaterials-induced macrophage-polarized activation could provide new basis to optimize therapeutic approaches and improve patient outcomes.