Apparatus and methods are described including an implantable device shaped to define (a) at least two artery-contact regions, the artery-contact regions comprising struts that are configured to stretch an arterial wall by applying pressure to the arterial wall, and (b) at least two crimping regions that comprise locking mechanisms configured to prevent the crimping regions from becoming crimped due to pressure from the wall of the artery on the artery-contact regions. The crimping regions are configured to be crimped during insertion of the device, via a catheter, by the locking mechanisms being unlocked during insertion of the device. Other embodiments are also described.