Tech.Mic (New York City, June 2) -- One early issue with nanobots is the risk of creating clots in the bloodstream when the 'bots are packed in tighter quarters. "When you talk to clinicians, one thing that makes them go white and never want to talk to you again is any kind of notion of putting something solid in the bloodstream," says, John Rogers, a MatSE professor at Illinois. "There are just really serious consequences of any kind of structure that's free-floating and just traveling around."