ADAMI, RENATA

REVERCHON, Ernesto

English

Archivio della Ricerca - Università di Salerno

Ninth Conference on Supercritical Fluids and Their Applications Sorrento, Italy, 05-08 September 2010 – Ed. E. Reverchon  139 SAA produced nanostructured polymer microparticles loaded with magnetic nanoparticles  Renata Adami*, Ernesto Reverchon  Department of Chemical & Food Engineering. University of Salerno Via Ponte Don Melillo, 84084 Fisciano (SA), ITALY.  Research center for nanomaterials and nanotechnology Via Ponte Don Melillo, 84084 Fisciano (SA), ITALY.  * radami@unisa.it  Supercritical Assisted Atomization (SAA) is one of the most efficient supercritical fluid (SCF) based micronization techniques proposed in the literature. The SAA working principle suggests the possibility of producing composite microparticles, since multi-component solutions can be processed. Therefore, in this work, SAA has been applied to the formation of polymer microparticles loaded with magnetic nanoparticles starting from suspensions of nanoparticles in polymer-solvent solutions. Magnetic nanoparticles possess the ability to work at the cellular and molecular level for biological interactions; the encapsulation in a polymeric coating makes the particles biocompatible and provides a steric barrier to prevent nanoparticle agglomeration and avoid opsonization. Dextran and chitosan have been used as dispersing matrices for magnetic nanoparticles. Nanostructured microspheres ranging between 0.2 and 1.5 µm with nanoparticle loading up to 20% have been obtained. They have been characterized by SEM, EDX, TGA, obtaining information on the morphology, particle size distribution, nanostructure and loading of nanoparticles in the polymeric matrices.  INTRODUCTION Using traditional micronization processes, it is very difficult to obtain the required particle size distribution (PSD). Therefore, micronization techniques based on SCFs have been proposed that are promising for the production of nano and micro particles with controlled size and distribution [1]. Supercritical Assisted Atomization (SAA) is one of the most efficient Supercritical fluid (SCF) micronization techniques proposed in the literature [2]. The process is based on the solubilization of controlled quantities of SC-CO2 in liquid solutions containing a solid solute and on the subsequent atomization of the ternary solution through a nozzle. In this case, SC-CO2 plays both as co-solute being miscible with the solution to be treated, as well as atomization agent. A two steps atomization is obtained: the primary droplets produced at the outlet of the injector (pneumatic atomization) are further divided in secondary droplets by CO2 expansion from the inside of the primary ones (decompressive atomization). SAA process has been applied to the micronization of different kinds of compounds, among them pharmaceutical compounds [3-6], polymers and bio-polymers [7-9]. The SAA working principle suggests the possibility of producing composite microparticles, since multi-components solutions can be processed; indeed, SAA has been applied to the production of drug-polymer microparticles for the controlled release of active principles from nanostuctured polymer microparticles [10-11]. Adami and Reverchon 140 Magnetic nanoparticles (MNPs) possess the ability to work at the cellular and molecular level for biological interactions; the encapsulation in a polymeric coating makes the particles biocompatible, stable, and may serve as a support for biomolecules. Furthermore, polymeric coatings provide a steric barrier to prevent nanoparticle agglomeration and avoid opsonization. The magnetic properties of nanostructured polymer-iron oxide microparticles enable their use in numerous applications: as magnetic contrast agents in magnetic resonance imaging (MRI), as hyperthermia agents, where the magnetic particles are heated selectively by the application of an high frequency magnetic field and as magnetic vectors that can be directed by a magnetic field gradient towards a given location in the body, for targeted drug delivery [12-14]. In this work SAA has been applied to the formation of polymer microparticles loaded with nanometric iron oxide starting from suspensions of iron oxide nanoparticles in polymer-solvent solutions. Chitosan and dextran have been used as polymer considering their bio-compatibility for pharmaceutical formulations or local targeted drug delivery [10].  1 - MATERIALS AND METHODS Low molecular weight chitosan, dextran (mw 43000), magnetite (Fe3O4) nanoparticles, water, acetic acid were used for the experiments. SAA laboratory apparatus consists of two high-pressure pumps delivering the liquid solution and liquid CO2 to the saturator. The saturator is a high pressure vessel (I.V. 25 cm3) loaded with stainless steel perforated saddles which assure a large contact surface between liquid solution and CO2. The solution obtained in the saturator is sprayed through a thin wall 80 µm diameter injection nozzle into the precipitator (I.V. 3 dm3) operating at atmospheric pressure. A controlled heated flow of N2 is sent to the precipitator to assist liquid droplets evaporation. A stainless steel filter located at the bottom of the precipitator allows the powder collection and the gaseous stream flow out. SAA apparatus layout and further details on the experimental procedures were published elsewhere [2]. The compounds to micronize were dissolved in 1% v/v acetic acid aqueous solution and, then, delivered to the SAA apparatus. Nanostructured microparticles were observed by a Scanning Electron Microscope (SEM) coupled with a field emission source (FE-SEM). Particle size (PS) and particle size distribution (PSD) were measured from SEM photomicrographs using the Sigma Scan Pro Software. Fourier transform infrared (FT-IR) spectra were obtained via M2000 FTIR, at a resolution of 0.5 cm-1. Microanalysis was used to investigate the particle chemical structure. Elemental analysis and element mapping were conducted with the field emission-scanning electron microscope (FESEM) equipped with an energy dispersive X-ray spectroscopy (EDX). The loading of MNPs in the polymeric matrix was determined by thermogravimetric analysis (TGA). Solid state analysis of the samples (XRPD=X-ray powder diffraction) was performed using an X-ray powder diffractometer (Bruker) with a Cu sealed tube source. The measuring conditions were: Ni-filtered CuKα radiation, λ=1.54 A, 2θ angle ranging from 5 to 70° with a scan rate of 3 s/step and a step size of 0.02°.  2 – RESULTS AND DISCUSSION Microparticles were produced operating at 100 bar and 85°C in the saturator, mass flow ratio between CO2 and liquid solution R=1.8 and a precipitation temperature of 110°C. The particles were spherical and amorphous at all the percentages of Fe3O4 loaded in the carrier. This can be observed, for example, in the SEM photomicrographs in figure 1, that reports the particles with a starting loading of MNPs of 10 and 30% (MNPs wt/polymer wt). Ninth Conference on Supercritical Fluids and Their Applications Sorrento, Italy, 05-08 September 2010 – Ed. E. Reverchon  141   figure 1. SEM photomicrographs of chitosan microparticles loaded with 10% (top) and 30% (down) of Fe3O4 MNPs Uniformly nanostructured microparticles ranging between 0.2 and 1.5 µm with Fe3O4 loadings have been obtained. Several concentrations of MNPs in the polymer in the starting solution have been processed, to understand the relation between the loading in the starting solution and the loading in the obtained particles (table 1).  Fe3O4/polymer, wt% Fe3O4 theoretic, wt% Fe3O4 effective, wt% encapsulation, % 5 4.76 3.50 73.50 10 9.09 6.20 68.20 15 13.04 7.60 58.27 20 16.67 11.17 67.02 30 23.08 17.80 77.13 40 28.57 19.20 67.20 table 1. loading of Fe3O4 in chitosan microparticles produced by SAA TGA analysis showed that the encapsulation efficiency of Fe3O4 in chitosan varies from 58 to 77%. It is possible to note that there is not a trend in the encapsulation efficiency depending from the Fe3O4 loaded as a suspension in the starting polymer solution, therefore, the efficiency might be strictly related to the preparation of the suspension. The MNPs loaded in the polymeric microparticles also affect the PSD: increasing the Fe3O4 percentage, the size of the particles decreases (figure 2). In particular, in the case of a loading of 30%, Adami and Reverchon 142 corresponding to an effective loading of MNPs of 17.8% wt/particle wt, the particles are smaller than 1 µm.  figure 2. PSDs in terms of volumetric cumulative percentage of chitosan microparticles loaded with Fe3O4 MNPs This result can be explained with a decrease of viscosity of the polymeric solution with the increase of MNPs loading: the increase of nanoparticles percentage suspended and uniformly distributed reduces the viscosity of the liquid solution, resulting in the formation of smaller primary droplets, that also influence the dimensions of the secondary droplets, improving the atomization of the solution [8-9]. XRPD analyses confirmed the presence of the nanoparticles in the polymeric matrix and FTIR showed no bounds between the polymer and the Fe3O4. The uniform dispersion of MNPs in the polymer microspheres was verified using EDX technique. Very interesting results have been obtained also using dextran as polymer. Loadings of Fe3O4 MNPs of 23.47% wt/particle wt have been obtained, with a very high encapsulation efficiency. In figure 3 a SEM photomicrograph of dextran particles produced operating at 84 bar and 85°C in the saturator, mass flow ratio between CO2 and liquid solution R=1.8 and a precipitation temperature of 110°C is reported.  figure 3. SEM photomicrographs of dextran microparticles loaded with 23.47% of Fe3O4 MNPs Ninth Conference on Supercritical Fluids and Their Applications Sorrento, Italy, 05-08 September 2010 – Ed. E. Reverchon  143 The particles were spherical and XRPD analyses showed that they are amorphous and the Fe3O4 peaks confirmed the presence of the nanoparticles that did not change their structure. Also in the case of dextran loaded microparticles, increasing the effective loading of Fe3O4, the PSD strongly decreases (figure 3). This confirms that the MNPs act as viscosity reducer, helping the rupture of the jet at the exit of the nozzle.  figure 4. PSDs in terms of volumetric cumulative percentage of dextran microparticles loaded with Fe3O4 MNPs Also in the case of dextran-MNP microparticles, EDX confirmed that the Fe3O4 nanoparticles were uniformly distributed in the polymeric matrix.  ACKNOWLEDGEMENTS The authors gratefully acknowledge Eng. Michela Memoli and Eng. Marianna Molletta for the help in performing the experiments. The MiUR (Italian Ministry of Scientific Research) is acknowledged for the partial financial support.  REFERENCES [1] J. Jung, M. Perrut. J Supercrit Fluid, Vol. 20(3), 2001, p. 179. [2] E. Reverchon. Ind Eng Chem Res, Vol. 41(10), 2002, p. 2405. [3] R. Adami, L. S. Osseo, E. Reverchon. Biotechnol Bioeng, Vol. 104(6), 2009, p. 1162. [4] G. Della Porta, C. De Vittori, E. Reverchon. Aaps Pharmscitech, Vol. 6(3), 2005, p. E421. [5] E. Reverchon, R. Adami, G. Caputo. Aaps Pharmscitech, Vol. 8(4), 2007, p. 272. [6] E. Reverchon, G. Della Porta. J Supercrit Fluid, Vol. 26(3), 2003, p. 243. [7] E. Reverchon, R. Adami, S. Cardea, G. Della Porta. J Supercrit Fluid, Vol. 47(3), 2009, p. 484. [8] E. Reverchon, A. Antonacci. Ind Eng Chem Res, Vol. 45(16), 2006, p. 5722. [9] E. Reverchon, A. Antonacci. J Supercrit Fluid, Vol. 39(3), 2007, p. 444. [10] E. Reverchon, A. Antonacci. Biotechnol Bioeng, Vol. 97(6), 2007, p. 1626. [11] E. Reverchon, G. Lamberti, A. Antonacci. The Journal of Supercritical Fluids, Vol. 46(2), 2008, p. 185. [12] M. Arruebo, R. Fernández-Pacheco, M. R. Ibarra, J. Santamaría. Nano Today, Vol. 2(3), 2007, p. 22. Adami and Reverchon 144 [13] T. K. Jain, J. Richey, M. Strand, D. L. Leslie-Pelecky, C. A. Flask, V. Labhasetwar. Biomaterials, Vol. 29(29), 2008, p. 4012. [14] C. Sun, J. S. H. Lee, M. Zhang. Advanced Drug Delivery Reviews, Vol. 60(11), 2008, p. 1252.  

SAA produced nanostructured polymer microparticles loaded with magnetic nanoparticles

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SAA produced nanostructured polymer microparticles loaded with magnetic nanoparticles

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