A penile prosthesis is disclosed that can alternate between an erect and flaccid state based on the shape memory properties of an exoskeleton that is responsive to increases and decreases in temperature. The exoskeleton consists of a shape memory alloy, such as nitinol, which in the erect configuration can radially expand and resist axial loads and buckling forces during coitus. The shape memory alloy is temperature-tuned to undergo a change to an erect state under external application of heat and can revert to a flaccid state with cooling below resting penile temperature.