Abstract: The present invention relates to devices for displacing two bodies relative to each other. The device of the invention is made up of two pieces respectively associated with the two bodies, a mechanism for applying a force between the two pieces, a projecting portion secured to the piece, a cavity complementary to at least a part of the projecting portion formed in the other piece, the pieces being displaceably mounted relative to each other in such a manner that the projecting portion engages in the cavity, the piece in which the cavity is formed being of a first material that is suitable for passing from an undeformable hard first state to a deformable soft second state, while the piece which is secured to the projecting portion is of a substantially undeformable second material, and a controller for controlling the passage of at least the portion of the first material that surrounds the cavity from the first state to the second state, and vice versa.