Uniform double-walled polymer microspheres of controllable shell thickness

A method for fabricating uniform double-walled microspheres with controllable size and shell thickness has been developed. The method, based on previous work to fabricate uniform microspheres, employs multiple concentric nozzles to produce a smooth coaxial jet comprising an annular shell and core material, which is acoustically excited to break up into uniform core-shell droplets. The orientation of the jets, material flow rates, and rate of solvent extraction are controlled to create uniform and well-centered "double-walled" microspheres exhibiting a controllable shell thickness. Double-walled microspheres were fabricated with different arrangements of bulk-eroding poly(D,L-lactide-co-glycolide) (PLG) and surface-eroding poly[(1,6-bis-carboxyphenoxy) hexane] (PCPH). Variation of the fabrication parameters allowed complete encapsulation by the shell phase, including the efficient formation of a PCPH shell encapsulating a PLG core. Utilizing this technology, double-walled microsphere shell thickness can be varied from <2 μm to tens of microns while maintaining complete and well-centered core encapsulation for double-walled microspheres near 50 μm in overall diameter.