A device is provided that is non-rigid, i.e., flexible and/or malleable, in a first form, and then transformable after insertion to an in vivo site into a rigid, or hardened, form; a cure-initiating energy is applied to the device; and the device is then positioned in the in vivo site where it hardens to provide a load-bearing function or other structural and/or mechanical function. The device includes a biocompatible sheath and a curable material sealed within the sheath. The curable material is provided in a first form that provides flexibility to the device and is structured to rigidize in a second form after application of a quantity of an initiating energy to the material.