You need a Kinematic Mount. There are many forms. The simplest form is called 3-2-1 and uses three non-collinear vertices. Pick one vertex and hold it with 3 constraints: X,Y,Z = 0. Pick a second vertex, some distance along X from the first point and hold it with 2 constraints: Y,Z = 0. Pick a third vertex, some distance in Y from the first point and hold it with 1 constraint: Z = 0. All expansion will be relative to the first point.
Another form of Kinematic Mount uses three vertices around a circle and requires a cylindrical coordinate system. The three vertices all have Theta and Z = 0 and Radial is Free. That is exactly six constraints, same as the 3-2-1 but all expansion is relative to the center of the circle. That would be nice for a stent which is a cylindrical object, but either one will allow free expansion of the metal stent with a pressure applied to the inner surface.