Novel co-axial electrohydrodynamic in-situ preparation of liquid-filled polymer-shell microspheres for biomedical applications

Suspensions consisting of polymer-shelled microspheres are finding increasing use in a diverse range of technologies orapplications, e.g. in the medical field, such as diagnostic imaging, drug and gene delivery and tissue engineering. In this work, asolution of water-insoluble polymethylsilsesquioxane was perfused through the outer needle of a co-axial needle arrangementwhile air was passed simultaneously through the inner needle, with both needles placed in an electric field. The liquid and air flowrates were varied but at 5 μl sÀ1 for each material stable microbubble formation was achieved at 5.7 kV. The microbubbles werecollected in a vial of distilled water and they rapidly converted into polymer-shelled microspheres containing $60 wt% liquid.Microscopic examination of the spheres within 300 s of preparation showed a large population of near-spherical polymer-shelledmicrospheres with a mean size of 6 Æ 2 μm diameter near the water surface. After 48h, the microspheres had collected at thebottom of the vial. The fact that the microspheres absorbed and encapsulated the liquid in which they were collected and the factthat their size (<10 μm) is suitable for vascular administration make this a new one-step preparation technology for microspheresused in biomedical applications.