"Tiny robots powered by living muscle have been created by scientists at the University of California, Los Angeles. The devices were formed by "growing" rat cells on microscopic silicon chips, the researchers report in the journal Nature Materials. Less than a millimetre long, the miniscule robots can move themselves without any external source of power. Muscles like these could be used in a host of microscopic devices - even to drive miniature electrical generators to power computer chips."
http://science.slashdot.org/article.pl?sid=05/01/17/1738204