Electrolytic detachment for implantable devices

Delivery and detachment of an implant can be enhanced by a retraction mechanism to secure portions of a delivery wire within an interior space of the implant. A delivery system can include an implant having a proximal end portion. A delivery wire can include (i) a detachment zone proximal to the proximal end portion and (ii) a distal region distal to the proximal end portion. An expansion member can be located between the proximal end portion and the distal region of the delivery wire. The expansion member can be biased to move the distal region of the delivery wire distally away from the proximal end portion when severed at the detachment zone.