Optimising the shell thickness-to-radius ratio for the fabrication of oil-encapsulated polymeric microspheres

Core–shell microspheres with controllable shell thickness-to-radius ( T / R ) ratios were fabricated using coaxial electrospraying for hydrophobic drug delivery using Sudan Red (dye) as a model hydrophobic active. Systematic investigations were conducted to determine the effects of several parameters on the particle diameter, shell thickness, and structure. These included polymer concentration, flow rate, applied voltage, collection distance and needle-to-ground electrode distance. The resulting microspheres were characterized by SEM and optical microscopy, which showed spherical core–shell geometries with tunable particle diameters and T / R ratios ranging from 30 to 70   μm and between 0.12 and 0.3, respectively. FTIR was used to assess material stability during the one-step preparation of microspheres. MTT assay and fluorescence microscopy indicated no significant effect on cell growth behavior over a 24   h period when assessed using variable particle concentrations (between 10   μg/ml and 10   mg/ml). In-vitro release of the oil-soluble dye exhibited a fast release onset followed by a sustained release which was controlled by changing particle size or T / R ratio. The results indicate potential applications for core–shell encapsulation and controlled release of hydrophobic drugs using the materials and processes described.