A new process for making reservoir-type microcapsules using ink-jet technology and interfacial phase separation

A new microencapsulation technique that utilizes interfacial mass transfer between two mutually soluble liquids has been developed. The technique is based on formation of a solid polymer film at the interface of a solution of a water-insoluble polymer and an aqueous solution, resulting from the mutual mass transfer of solvents (i.e., solvent exchange). Reservoir-type microcapsules were prepared by inducing this phenomenon to occur on the surface of an aqueous droplet. One method of implementation employed a dual microdispenser system that consisted of two ink-jet nozzles. The nozzles, producing droplets of a polymer solution and an aqueous drug solution, respectively, were aligned to allow collision of pairs of the droplets. The collision resulted in spreading of the polymer solution on the aqueous droplet and simultaneous solvent exchange, to form a polymeric membrane around the aqueous droplet. The formation of the polymer membrane depended largely on the favorable spreading of the polymer solution on the aqueous droplets and fast solvent exchange, and required judicious selection of the organic solvent. Simple and fast screening methods were developed for selection of a proper solvent. Ethyl acetate was chosen as one of the most desirable solvents through the screening procedures. Ethyl acetate and the dual microdispenser system were used to form microcapsules that were subsequently examined by microscopic methods to demonstrate their unique geometry.