Development of carbonyl iron/ethylcellulose core/shell nanoparticles for biomedical applications

A reproducible method for the preparation of mixed colloidal nanoparticles, consisting of a magnetic carbonyl iron nucleus and a biocompatible ethylcellulose latex shell, is described in this article. The heterogeneous structure of the particles can confer them both the possibility of being used as drug delivery systems and the responsiveness to external magnetic fields, allowing a selective guidance of drug molecules to specific target tissues without a concurrent increase in its level in healthy tissues. The preparation method is based on an emulsion solvent evaporation process. A complete physicochemical characterization of the composite particles was carried out, and this preliminary investigation showed that the surface behavior of the core/shell particles is similar to that of bare ethylcellulose particles. This was confirmed, in particular, by zeta potential determinations as a function of pH and ionic strength. This fact points to the ethylcellulose shell efficiently coating carbonyl iron, and leading to composite particles which, from the electrokinetic point of view, are almost indistinguishable from latex. The thermodynamic analysis agrees with the electrokinetic one in suggesting that the coverage has been complete, since the components of the surface free energy of mixed particles coincide almost exactly with those corresponding to the cellulose-based pseudolatex. Moreover, the hydrophilic nature of carbonyl iron is modified and the particles become hydrophobic, just like the latex, when they are covered by ethylcellulose. The magnetic behaviors of the carbonyl iron and composite particles were also checked, and the similarities between both types of particles were demonstrated, except that the polymeric shell reduces the magnetization of the sample. (C) 2007 Elsevier B.V. All r rights reserved.