J. of Supercritical Fluids 82 (2013) 34–40 Contents lists available at ScienceDirect The Journal of Supercritical Fluids jou rn al hom epage: www.elsevier.com/locate/supflu Lipid nanoparticles production by supercritical fluid assisted emulsion–diffusion Roberta Campardelli a , Maxime Cherain b , Claire Perfetti b , Carlo Iorio b , Mariarosa Scognamiglio a , Ernesto Reverchon a , Giovanna Della Porta a,b,c,∗ a Department of Industrial Engineering, Università di Salerno, via Ponte don Melillo, 84084 Fisciano, SA, Italy b Microgravity Research Center, Chimie-Physique Lab., Université Libre de Bruxelles, Avenue P. Heger, 1050 Bruxelles, Belgium c Research Centre for Nanomaterials and nanoTechnology (NANOMATES), Università di Salerno, via Ponte don Melillo, 84084 Fisciano, SA, Italy a r t i c l e i n f o Article history: Received 15 February 2013 Received in revised form 25 May 2013 Accepted 28 May 2013 Keywords: Lipid nanoparticles Supercritical fluid Continuous processing Emulsion/diffusion a b s t r a c t In this work a supercritical technology is proposed to improve the classical emulsification/diffusion tech- nology for lipid nanoparticles (LNs) production. The process is based on the emulsion diffusion method improved by the addition of a continuous supercritical fluid processing step to eliminate the organic solvent from the nanosuspension obtained. Different emulsion/diffusion formulations for stearic acid nanoparticles production were tested and, then, processed by supercritical continuous extraction at 80 bar and 45 ◦ C (liquid/gas ratio of 0.1) in a packed column, obtaining an efficient benzyl alcohol elimination. Solvent residues less than 100 ppm were measured. Stearic acid nanoparticles were not extracted or damaged by the supercritical processing step, did not stick on the packing elements and showed mean diameters of 30–50 nm; a value of one order of magnitude smaller than the ones obtained by the conventional emulsion/diffusion technology with a recovery efficiency of 100%. Indeed, the fast and complete elimination of the benzyl alcohol around the nanoparticles reduced the aggregation phenomena responsible of larger lipid particle sizes obtainable by traditional process. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The production of drug nanocarriers able to overcome ther- apy failures, such as, poor absorption or specific drug targeting, is one of the challenges of the modern nanomedicine. Nanocarriers can be emulsions, micelles, liposomes or polymer particles [1,2]. Recently, lipid nanoparticles (LNs) have been proposed as nano- systems that may have the advantage of combining the properties of polymer nanoparticles, for convenient drug sustained release [3–5], fat based systems for low toxicity [6,7], and effective tar- geting [8]. Moreover, the use of LNs for parental, topical and oral administration has been proposed in very promising medical appli- cations [9–11]. LNs suspension is formed as a rule by: a lipid matrix, a stabilizing agent (emulsifiers/surfactants), a continuous medium (water) and can contain residues of the organic solvents used, depending on the manufacture techniques adopted [12]. The term lipid is referred to various kinds of molecules like: triglycerides, glycerides, fatty acids, steroids and waxes. However, triacylglycerides are commonly used ∗ Corresponding author at: Department of Industrial Engineering, University of Salerno, I-84084 Fisciano, SA, Italy. Tel.: +39 089964104; fax: +39 089964056. E-mail address: gdellaporta@unisa.it (G. Della Porta). as lipid carriers due to their polymorphic behavior that improves the stability of the nanoemulsion and allows a high drug loading by the less ordinate structure of the lipid matrix. The choice of the lipid to be used can be greatly influenced by the drug to be loaded and by the specific target required. Surfactants or surfac- tant combinations could greatly influence the particle size and the stability of the dispersion, as well as, play an important role in con- trolling the LNs crystallization process. Indeed, due to nanosize of the particles, the number of lipid molecules that interacts with the surfactant molecules can be large enough to influence the crys- tallization process and it has been demonstrated that a mixture of nonionic (crystal modulation) and ionic surfactant (stabiliza- tion) is recommended to fulfill both criteria of dispersion stability and crystal modulation [13]. In addition, the choice of the emul- sifier is largely dependent on the administration route, as well as, the organic solvent used, which should be chosen, as non-toxic, as possible. Current methods to produce LNs include high-pressure homogenization [14,15], microemulsion technique [16], sol- vent emulsification/evaporation [14,17] and solvent emulsifi- cation/diffusion [18,19]. In the high pressure homogenization technique, lipids are heated above their melting temperature; then, poured into hot surfactant solution, homogenized and cooled to crystallize the lipid droplets and obtain nanoparticles. 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