A stent (120) has proximal and distal ends (140, 142), and is configured to assume radially-compressed and radially-expanded states. The stent (120) comprises a plurality of circumferential bands (122) disposed about a longitudinal axis (123) of the stent (120), each of which bands (122) comprises a plurality of struts (124) connected to one another. At least one of the bands (122) is shaped so as to define a plurality of distally-directed peaks (126) alternating with a plurality of proximally-directed troughs (128), and one or more strain-concentration modules (132). Each of the modules (132) has a central axis (156) parallel to the longitudinal axis (123) of the stent (120), and comprises: (a) an open loop section (150), which comprises one of the distally-directed peaks (126); (b) a primary neck section (152); and (c) a secondary section (154). Other embodiments are also described.