Variable stiffness devices and methods of their use are provided. In some embodiments, a variable stiffness device comprises an inner member defining a compartment for receiving an actuating fluid; an outer member disposed around the inner member; and a granular medium disposed between the inner member and the outer member; wherein the inner member is being moveable in a radial direction from a relaxed state to an expanded state by introducing the actuating fluid into the compartment of the inner member to compress the granular medium against the outer member to increase the stiffness of the device.