Abstract: The present invention provides a method for the formation of a medical device that comprises a therapeutic agent and a release region, which regulates the rate at which the therapeutic agent is released from the medical device. The method comprises providing a precursor region that comprises a polymer composition comprising two or more microphase separated polymer domains that are immiscible with one another, and forming said release region by a process that comprises applying an orienting field comprising an electric field, a magnetic field, a mechanical shear field, or a solvent gradient field, or a combination of two or more fields to said precursor region, wherein said field or combination of fields changes the spatial orientation of the microphase separated polymer domains within the release region. The electric, magnetic, mechanical shear or solvent gradient field is of sufficient strength to change the spatial orientation of the microphase separated domains.