Preparation and evaluation of uniformly sized solid lipid microcapsules using membrane emulsification

Uniformly sized solid lipid microcapsules (SLMCs) were prepared by temperature-controlled membrane emulsification using a high-melting-point triglyceride (tripalmitin) as the encapsulating material. Water-in-oil-in-water (W/O/W) emulsions with a narrow droplet diameter distribution and encapsulating vitamin B12 as a model drug were prepared by a two-step membrane emulsification technique using Shirasu porous glass membranes with a mean pore diameter of 0.3–9.9 μm, at a higher temperature (343 K) than the melting point of the oil phase containing tripalmitin. The resultant W/O/W emulsions were immediately cooled to solidify the oil phase, and were then filtered. Uniformly sized SLMCs with high encapsulation yields of vitamin B12 of 93.2–97.7% (w/w) were obtained, and the mean particle diameter was 3.1–32.8 μm, which was almost the same as the mean diameter of the oil droplets containing the inner water phase of the corresponding W/O/W emulsion. The mean particle diameters of the SLMCs could be determined by the membrane pore diameters used. No leakage of vitamin B12 from the uniformly sized SLMCs was observed at body temperature (310 K) or below over a period of 10 days, when the SLMCs were re-dispersed into normal saline. The SLMCs had a high thermal stability below body temperature (310 K) over 10 days.