Insulator layers for leads of implantable electric stimulation systems and methods of making and using

An implantable lead comprising:

• an elongated member having a distal end portion, a proximal end portion, and a longitudinal length;
• a plurality of electrodes disposed along the distal end portion of the elongated member;
• a plurality of terminals disposed along the proximal end portion of the elongated member;
• a plurality of conductors, each conductor electrically coupling at least one of the electrodes to at least one of the terminals, wherein at least one of the conductors comprises at least one unit, the at least one unit comprising
• a first conductor segment extending along the elongated member from a beginning point to a first position,
• a second conductor segment extending along the elongated member from the first position to a second position, and
• a third conductor segment extending along the elongated member from the second position to an endpoint,
• wherein the first position is between the second position and the endpoint, and the second position is between the beginning point and the first position,
• wherein the conductor segments are arranged so as to form a plurality of single-coil regions and a plurality of multi-coil regions,
• wherein the plurality of single-coil regions and the plurality of multi-coil regions are arranged along the longitudinal length of the elongated member in an axially alternating configuration with each individual single-coil region of the plurality of single-coil regions abutted by at least one multi-coil region of the plurality of multi-coil regions;
• an inner insulator layer disposed along the entire longitudinal length of the elongated member between the plurality of electrodes and the plurality of terminals, wherein the inner insulator layer is formed of a material that has a first melting point and that is flowable when applied to the conductors to fill in at least some open spaces between portions of at least one of the units;
• and
• an outer insulator layer disposed over the inner insulator layer along the entire longitudinal length of the elongated member between the plurality of electrodes and the plurality of terminals, wherein the outer insulator layer has a second melting point;
• wherein at least one of the inner insulator layer or the outer insulator layer is formed from a doped material;
• wherein each of the plurality of single-coil regions is completely encased by the inner insulation layer;
• wherein each of the plurality of multi-coil regions is partially encased in the inner insulation layer and partially encased in the outer insulation layer;
• wherein the first melting point is different from the second melting point.