Introduction: Anisotropic polymeric particles such as toroidal microparticles are potential for drug delivery. Toroidal microparticles have large specific surface area and short diffusion distance of molecules, which yields the difference in release kinetics of drugs. Recently, torus-shaped alginate microparticles (TSMs) for cell encapsulation were prepared via vortex-ring freezing method by Ma Minglin and Luo Dan et al. In this study, we fabricated drug encapsulated TSMs with electrospray and analyzed the release kinetics of model drugs from TSMs. Materials and Methods: Model drug encapsulated TSMs were fabricated by vortex-ring freezing method. In short, sodium alginate solution was injected into the crosslinking solution with high voltage. The droplet formed toroidal flow, vortex-ring, in the crosslinking solution and fixed the shape of the fluid by crosslinking. After the fabrication, post-crosslinking method adding the solution with high cationic concentration of Ca, Sr, and Ba was conducted to enhance the chemical stability and mechanical strength. The swelling and degradation behavior and release of drugs were evaluated with confocal laser scanning microscope and fluorometer. Results and Discussion: The outer and inner diameter of TSMs encapsulating dextran (70 kDa) were 194 ± 33 μm and 101 ± 20 μm. In addition, several model drugs of different molecular weight and electrical charge were successfully encapsulated in TSMs with large concentration range. Post-crosslinking process reinforced the mechanical strength of TSMs and stabilized the TSMs, extending the degradation time of TSMs in Tris buffer. Especially, TSMs post-crosslinked with barium chloride remained in Tris buffer over two weeks. The release kinetics of the model drugs was categorized into two groups: diffusion-controlled release and degradation-diffusion controlled release. In the latter case, the release rate of the drugs was controlled with post-crosslinking. These results indicate the usefulness of TSMs as a unique drug release carrier in the future.

Preparation of torus-shaped alginate microparticles for drug delivery by vortex-ring freezing method

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