According to a recent NewScientist.com article, researchers at the University of California, led by Feynman prize winner Carlos Montemagno, have succeeded at created a biologically powered nanomechanical system. What they've created is a tiny robot actuated by cardiac muscle that was grown in place on the robot and is powered by a glucose nutrient. Montemagno has been working on the program of nanoscale biomechanical systems for some time. For more on the musclebot, see this more detailed scotsman.com article or the recent Wired News article