Fabrication of hollow poly-allylamine hydrochloride/poly-sodium styrene sulfonate microcapsules from microbubble templates

Hollow microcapsules made of biodegradable polymers have attracted considerable attention as ultrasound contrast agents and carriers in drug delivery systems (DDSs). A hollow polyelectrolyte microcapsule is one of the promising candidates for such applications. Hollow polyelectrolyte microcapsules are normally fabricated by decomposing a core material after forming a capsule shell. Recently, Shchukin et al. (D. G. Shchukin, K. Kohler, H. Mohwald and G. B. Sukhorukov, Angew. Chem., Int. Ed., 2005, 44, 3310-3314) and Winterhalter et al.(M. Winterhalter and A. F. P. Sonnen, Angew. Chem., Int. Ed., 2006, 45, 2500-2502) proposed a fabrication method of hollow polyelectrolyte microcapsules using microbubbles as templates. In this method, stable microbubbles are formed in a surfactant solution by means of an ultrasound generator, and then, a polyelectrolyte is adsorbed on the microbubble surface, yielding hollow polyelectrolyte microcapsules. In this study, we proposed a new fabrication method for hollow poly-allylamine hydrochloride/poly-sodium styrene sulfonate (PAH/PSS) microcapsules without using surfactants. In a Na(2)CO(3) aqueous solution, PAH becomes colloidal particles of R-NHCOO(-) and R-NH(3)(+) within a certain pH range. Under such a condition, if microbubbles are generated in the solution, the colloidal particles adsorbed on the microbubble surface stabilize the microbubbles. When PSS is added to the solution sequentially, a bilayer of PAH/PSS can be formed around microbubbles. We successfully fabricated hollow PAH/PSS microcapsules by this method and elucidated the conditions required for the formation of colloidal particles of PAH and a bilayer of PAH/PSS.