Biomechatronics is this really integrated field, combining biology with mechanical, electronic, and computer engineering for the design of nerve-connected prosthetics and other devices that can be temporarily or permanently attached to living things (namely, people). It's a great field, with the potential to let the blind see, the deaf hear, and the wheelchair-bound walk.
How do I get there? A small handful of universities offer it as a graduate degree. What would you recommend in terms of potential universities, undergrad engineering majors?