Synthesis of Core-Shell Biopolymer Particles Using Coaxial Electrospray
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Synthesis of Core-Shell Biopolymer Particles Using Coaxial Electrospray
Cho Hui Lim and Michael E. Mullins, Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931 ABSTRACT Core-shell PLLA microparticles were successfully fabricated using a novel coaxial nozzle design. These particles were synthesized with different components in the core/shell layers representing three classes of systems of interest for drug delivery applications: PVA/PLLA, PLLA/PEG, and oleic acid/PLLA. The components were characterized for their physical properties and interfacial energies, and optimal conditions for the operation were determined. To facilitate the particle characterization, each phase was doped with a different fluorescent dye to aid in the confirmation of a core/shell structure via fluorescence microscopy. INTRODUCTION Recent development in electrohydrodynamic processing focuses on micro- and nanoencapsulation, particularly for targeted drug delivery. The coaxial electrospraying was first demonstrated to introduce biomaterial into cells by Pui and Chen (2000) [1]. Coaxial electrospraying has since been extensively investigated in the literature [2-6]. Using coaxial electrospray, Loscertales et. al. (2002) produced monodisperse capsules in the submicron range. López-Herrera et. al. (2003) further investigated coaxial jets of two immiscible liquids generated from Taylor cones. Chen et. al. studied the spraying modes of coaxial electrospray. Mei and Chen (2007) further investigated the effect of surface tension on particle encapsulation. All the previously published works only focused on the electrified coaxial jet of two immiscible pure liquids. Xie et. al. (2008) demonstrated the encapsulation of protein drugs in biodegradable polymeric microparticles using coaxial electrospray. In their work, the optical images did not show that good spherical particles were obtained. Coaxial electrospraying is a simple, single-step method to form particles in the micron and submicron size range from liquid solutions of a broad variety of materials. In this process, two immiscible and co-flowing liquids are injected through two needles located one inside the other. The design challenge was to build a case that could hold and align the capillary needles concentrically and also to prevent the capillary needles from touching each other. In this paper, the fabrication of core-shell PLLA microparticles using a novel modified coaxial nozzle design is reported for the first time. EXPERIMENTAL METHODOLOGIES In this study we examined the electrospraying of 3 combinations of core/shell polymer systems that could be applicable to drug delivery systems: aqueous phase solute/bio-polymer shell, bio-polymer/hydrophilic polymer shell, and fatty acid/bio-polymer shell. In the first case, to emulate an aqueous core/polymer shell system, PLLA was used as the shell material, with polyvinyl alcohol (PVA) in water or a solvent mixture used as the core material. Specifically, 3 wt./vol.% PLLA was dissolved in 10 mL of dichlorometh
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