The present invention provides a microcapsule for implantation into a mammalian body, comprising: a) at least one cell and/or bioactive agent; and b) a biocompatible semi-permeable membrane encapsulating the at least one cell, wherein the biocompatible semi-permeable membrane comprises: at least one polycationic polymer region, at least one alginate polymer region, and a paramagnetic or superparamagnetic metal that does not participate in the crosslinking of the alginate polymer. The present invention further provides methods of making the microcapsules of this invention and use of the microcapsules of this invention in methods of delivering cells and/or therapeutic agents to a subject and in methods of embolization.