The invention features methods and apparatus for producing lipid nanoparticles. Methods of the invention include injecting a lipid solution into an aqueous solution at an automated rate (e.g., a rate controlled by a servo pump). The invention provides methods and apparatus for making lipid nanoparticles possessing a wide range of lipid components and hydrophilic encapsulants, including nucleic acids (e.g., mRNA). Also provided are nanoparticles and compositions thereof made by methods and apparatus of the invention.
