Scientists develop a 'nanosubmarine' that delivers complementary molecules inside cells

It's too preliminary to be all that encouraging yet, but such a "nanosubmarine" is the ultimate goal for maintaining biological health:

http://www.eurekalert.org/pub_releases/2014-06/uom-sda062514.php

Maybe it can use this to maneuver:

http://www.ats.org/news/worlds-smallest-propeller-could-be-used-for-microscopic-medicine/