An elongated device, e.g. an interventional guide wire or catheter, comprises an optical fiber (OF) arranged to allow transmission of light to phase change material (PCM) arranged long the elongated device, for optically heating the phase change material (PCM) to change its stiffness from one stiffness value to a different stiffness value. Using distributed tilted or blazed Bragg gratings with light wavelength dependent unique grating periods along the optical fiber, it is possible to provide a guide wire or catheter which can be stiffness controlled at selected longitudinal portions. Especially, it may be preferred to be able to control the behavior of the tip of a guide wire or catheter for optimal navigation, e.g. during a FEVAR procedure. Portions of phase change material (PCM-1, PCM 2) arranged inside a tube material T_M can be activated at selected longitudinal parts of the elongated device.

A guidewire formed from drawn filled tubing having an inner core member encased in an outer layer. The inner core member is formed from a linear elastic or superelastic material and the outer layer is formed from a metal alloy such as 35N LT. A portion of the outer layer is ground down to form a feather edged joint between the outer layer and the inner core member.