A protein corona is a dynamic coating of biomolecules, usually proteins, around the surface of a nanoparticle that forms spontaneously in colloidal nanomaterials upon exposure to biological mediums. Protein coronas can form in many different patterns depending on their size, shape, composition, charge, and surface functional groups, and have properties that vary in different environmental factors like temperature, pH, shearing stress, immersed media composition, and exposing time. These coatings are also changeable according to the conditions of the biochemical and physiochemical surface interactions. Types of protein coronas are known to be divided into two categories: “hard” and “soft”. “Hard” coronas have higher-affinity proteins that are irreversibly bonded to the nanoparticle surface, while “soft” coronas have lower-affinity proteins on the nanoparticle surface that are reversibly bound. These reversibly-bound proteins allow for the biomolecules in “soft” protein coronas to be exchanged or detached over time for various applications. This process is governed by the intermolecular protein-nanoparticle and protein-protein interactions that exist within a solution. In "soft" protein coronas, it is common to observe an exchange of proteins at the surface; larger proteins with lower affinities will often aggregate to the surface of the nanoparticle first, and over time, smaller proteins with higher affinities will replace them, "hardening" the corona, known as the Vroman effect.