Materials and systems that enable high efficiency conversion of mechanical stress to electrical energy and methods of use thereof are described herein. The materials and systems are preferably used to provide power to medical devices implanted inside or used outside of a patients body. For medical devices, the materials and systems convert electrical energy from the natural contractile and relaxation motion of a portion of a patients body, such as the heart, lung and diaphragm, or via motion of body materials or fluids such as air, blood, urine, or stool. The materials and systems are capable of being bent, folded or otherwise stressed without fracturing and include piezoelectric materials on a flexible substrate. The materials and systems are preferably fashioned to be generally conformal with intimate apposition to complex surface topographies.
