Layer-by-Layer Polyelectrolyte–Polyester Hybrid Microcapsules for Encapsulation and Delivery of Hydrophobic Drugs

A two-step process is developed to form layer-by-layer (LbL) polyelectrolyte microcapsules, which are able to encapsulate and deliver hydrophobic drugs. Spherical porous calcium carbonate (CaCO₃) microparticles were used as templates and coated with a poly­(lactic acid-<i>co</i>-glycolic acid) (PLGA) layer containing hydrophobic compounds via an in situ precipitation gelling process. PLGA layers that precipitated from <i>N</i>-methyl-2-pyrrolidone (NMP) had a lower loading and smoother surface than those precipitated from acetone. The difference may be due to different viscosities and solvent exchange dynamics. In the second step, the successful coating of multilayer polyelectrolytes poly­(allylamine hydrochloride) (PAH) and poly­(styrene sulfonate) (PSS) onto the PLGA coated CaCO₃ microparticles was confirmed with AFM and ζ-potential studies. The release of a model hydrophobic drug, ibuprofen, from these hybrid microcapsules with different numbers of PAH/PSS layers was investigated. It was found that the release of ibuprofen decreases with increasing layer numbers demonstrating the possibility to control the release of ibuprofen with these novel hybrid microcapsules. Besides loading of hydrophobic drugs, the interior of these microcapsules can also be loaded with hydrophilic compounds and functional nanoparticles as demonstrated by loading with Fe₃O₄ nanoparticles, forming magnetically responsive dual drug releasing carriers