Novel formulations of vitamins and insulin by nanoengineering of polyelectrolyte multilayers around microcrystals

Microcapsules loaded with vitamin K-3 (VK3), biotin, or insulin were prepared by using a novel coating technology based on the layer-by-layer (LbL) deposition of oppositely charged polyelectrolytes onto microcrystal templates. This produced multilayered, polymeric shells of varying thickness around the crystalline cores. Dissolution of the core material (VK3 with ethanol, biotin with basic solution, and insulin with acidic solution), resulted in its release through the shells. Microelectrophoresis was employed to monitor the microcrystal coating process; confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) were used to verify multilayer coating and the formation of hollow polymer shells following removal of the microcrystal templates. The release rates of both VK3 and insulin decreased as the wall thickness (the number of polyelectrolyte layers deposited onto the microcrystal cores), increased. The release time could be varied by a factor of more than ten, depending on the number of polyelectrolyte layers applied. Following the addition of 70 mass % ethanol, the solubility of VK3 increased by as much as 170-fold, resulting in an increased rate of VK3 release. By selecting appropriate polymer materials for the shells, and by controlling the number of polyelectrolyte layers applied, shells of various thickness, stiffness, aqueous solubility, dispersibility, biocompatibility, and permeability can be constructed.