To overcome this problem, Katzir and his colleagues developed a laser-based system with a feedback loop that prevents overheating. First, they had to determine the optimal temperature at which flesh melts but can still heal (about 65 degrees Celsius). Then the group created a pen-sized tool that incorporates optic fibers: one that channels a carbon dioxide-powered infrared laser to the wound with pinpoint precision, and another that leads from the pen to an infrared sensor, which measures the temperature and ensures that the heat remains within the ideal range, between 60 and 70 degrees. All a surgeon has to do is move the pen's tip along the cut, strengthening and sealing the weld with a solder of water-soluble protein.