Detachment of a medical device from a delivery assembly can focus activity of electrolytic detachment to enhance detachment procedures. Electrolytic activity can be focused by insulating nearby areas of a core wire and pre-treating a detachment zone to reduce crystallinity of the detachment zone. Such a delivery system, can include an electrolytically corrodible core wire comprising a proximal portion, a distal portion, and a detachment zone between the proximal portion and the distal portion a proximal insulating layer annularly contacting the proximal portion a coil helically winding about and contacting at least a portion of the proximal insulating layer a tube annularly contacting at least a portion of the helical coil a distal insulating layer annularly contacting the distal portion and a hub of an implant annularly contacting at least a portion of the distal insulating layer wherein a distal end of the proximal insulating layer and a proximal end of the distal insulating layer are axially spaced apart to expose the detachment zone.
