The invention provides methods of making and using compositions comprising a polymer shell designed to deliver polypeptides to selected environments. In embodiments of the invention, different environmental conditions are harnessed to allow the selective degradation of the polymer shell and the consequential release of one or polypeptides encapsulated therein. In illustrative embodiments, polymer components of the shell are interconnected by disulfide-containing crosslinker moieties, linkages which maintain the integrity of the polymer shell under certain environmental conditions including those occuring outside of cells, but degrade in an intracellular environment.
