We live in a world where we can't quite replace our internal organs without having another internal organ on standby. Every so often, there is a breakthrough in prosthetic, bionic limb technology, but humans can't quite replace their entire hearts or brains with a machine counterpart as of yet. The only thing we can do is add a machine supplement. Now, though, scientists at Harvard have built a machine spleen, which is able to remove pathogens from the bloodstream through the use of magnetic nanobeads.