Controlled release of hydrophilic entities, such as peptides, proteins and even pDNA, is difficult to accomplish with conventional approaches. This work suggests one possible approach for controlled release of such actives using electrospun core-shell fiber structures. In particular, we propose strategies for partition control of the release. The fibers consist of two layers, with the outer polymer sleeve serving containing the inner core, in which the drug is encapsulated. By varying the physical and chemical properties of the core and shell solutions, we have shown that the release rate of a hydrophilic drug, metoclopramide hydrochloride, is controllable. Experimental results show a clear difference in the release pattern between monolithic fibers made of hydrophilic and hydrophobic polymers and various core-shell fibers with PCL, PLLA and PLGA 80/20 as shell polymers. The study yields insight into when partition control of release can be achieved in core-shell fibers, and with that, options for controlled release systems for hydrophilic drugs, peptides and pDNA. (C) 2010 Published by Elsevier B.V.