The Use of Hydrophilic Poly(N,N-dimethylacrylamide) for Promoting Engulfment of Magnetic γ-Fe₂O₃ Nanoparticles by Mammalian Cells

γ-Fe₂O₃ nanoparticles obtained by coprecipitation of Fe(II) and Fe(III) chlorides with a base and subsequent oxidation were coated with a shell of hydrophilic biocompatible poly(N,N-dimethylacrylamide) (PDMAAm). Various initiators were attached to the iron oxide surface to enable the use of the “grafting-from” approach for immobilization of PDMAAm. They included 2,2′-azobis(2-methylpropanimidamide) dihydrochloride (AMPA), 2,2′-azobis(N-hydroxy-2-methylpropanimidamide) dihydrochloride (ABHA) and 4-cyano-4-{[1-cyano-3-(N-hydroxycarbamoyl)-1-methylpropyl]azo}pentanoic acid (CCHPA). Engulfment of PDMAAm-coated γ-Fe₂O₃ nanoparticles by murine J774.2 macrophages was investigated. Only some nanoparticles were engulfed by the macrophages. PDMAAm-AMPA-γ-Fe₂O₃ and PDMAAm-ABHA-γ-Fe₂O₃ nanoparticles were rapidly engulfed by the cells. In contrast, neat γ-Fe₂O₃ and PDMAAm-CCHPA-γ-Fe₂O₃ particles induced formation of transparent vacuoles indicating toxicity of the particles. Thus, PDMAAm-coated AMPA- and ABHA-γ-Fe₂O₃ nanoparticles can be recommended as non-toxic labels for mammalian cells.