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 .