Comparison of post-emulsification freeze drying or spray drying processes for the microencapsulation of plasmid DNA

In this work, methods used to microencapsulate plasmid DNA in a biodegradable polymer were compared for their effects on the physicochemical characteristics of DNA-loaded microparticles and on the release and integrity of encapsulated DNA. Microparticles were formulated by either w/o/w emulsification and freeze-drying (EFD) or by w/o/w emulsification and spray-drying (ESD). The influence of both manufacturing processes on particle morphology, charge, release characteristics and biological activity of encapsulated DNA was evaluated. Particles produced by emulsification/spray-drying exhibited more diversity in shape and size than those produced by emulsification/freeze-drying. These particles also exhibited higher plasmid DNA encapsulation efficiency than particles produced by emulsification/freeze-drying. The fractional DNA release rates were similar over the first 25 days for both formulations, release rate declining more rapidly at later times for the ESD product. Mammalian cell transfection assays confirmed the biological activity of encapsulated DNA extracted from both types of particles, with significantly higher transfection levels being observed for ESD particles. Application of a double emulsion (w/o/w) before spray drying resulted in higher encapsulation levels (> 90%) relative to previous literature values, which used single (w/o) emulsions before spray drying. The emulsification/spray-drying technique described here appears to be a rapid and efficient method for the preparation of PLGA microparticles loaded with plasmid DNA.