Limor Schweitzer is obsessed with understanding humanoid locomotion and using that knowledge to make humanoid robots. He also runs RoboSavvy, a UK-based company which has become a retailer of robotics equipment for hobbyists and researchers in Europe. Along the way, Schweitzer's company has established expertise in 3D printers, and MakerBot 3D printers in particular. That experience has led them to create the MM2X - Multi-Material Dual Extruder - a replacement dual extruder system for the MakerBot Replicator 2X. It's an improvement over the standard nozzle system for those machines that makes multi-material printing with the Replicator 2X possible. You can read the whole story here: http://3dprint.com/68888/robosavvy-mm2x-dual-extruder/
Below is a look at a MakerBot Replicator 2X with the MM2X in place: