Oil-in-oil microencapsulation technique with an external perfluorohexane phase

Commonly, the microencapsulation of a lipophilic drug in a polymeric matrix via an ordinary oil/oil emulsification allows entrapping limited drug amounts due to its loss into the external phase. In this present paper, a new microencapsultion method describes the use of perfluorohexane as an external oil phase in order to produce microparticles of polyvinylpyrrolidon/vinylacetate (copovidone) and Eudragit® RS. Due to its highly non-solvent properties to most compounds, very limited miscibility with organic solvents, and very low toxicity, perfluorohexane (PFH) represents an excellent liquid for an external phase of the emulsion. Copovidone and Eudragit® RS microparticles were prepared by an oil/PFH method trapping ibuprofen as a lipophilic model drug and compared to results from conventional methods (oil/water and oil/oil). Morphological analyses of the obtained particles underlined the general matrix structure. The particle size varied between 75 μm (oil/oil) and 400 μm (oil/PFH) largely influenced by the stirring speed. Although drug release kinetics were principally similar for all preparation methods, it was generally found that encapsulation rates of oil/water and oil/PFH systems (oil/water: 74 ± 9%; oil/PFH: 86 ± 10%) were superior to ordinary oil/oil emulsification (3 ± 1%). The use of PFH was found to be a new promising tool for the preparation of microparticles. This modified emulsification method allowed the entrapment of lipophilic drugs into hydrophilic or lipophilic polymers in the absence of an aqueous phase.