Porous polymers having a plurality of openings or chambers that are highly convoluted, with each chamber being defined by multiple, thin, flat partitions are produced by a new gel enhanced phase separation technique. In a preferred embodiment, a second liquid is added to a polymer solution, the second liquid causing the solution to increase in viscosity. With sufficient polymer and second liquid present, the increase in viscosity can be up to that of a gel. The gel can then be shaped as needed. Subsequent solvent extraction leaves the porous polymeric body of defined shape. The porous polymers have utility as medical prostheses, the porosity permitting ingrowth of neighboring tissue. A second material may be incorporated into the chambers, thereby creating a microstructure filling the voids of the macrostructure. A porous polymeric body manufactured by this process may incorporate biologically active agents, and which agents may be delivered in a time-staged delivery manner, where differing drugs may be delivered over differing periods.