Sure, 3D printers that can spit out chocolates, create shoes, handcraft cars and help astronauts sound fun and magical, but a lot of scientists are working to make models that aren’t just fun. They’re developing 3D printers that can also save and change lives by printing out functional human organs. Think about it: If we can make organs on demand, patients don’t have to wait as long for transplanted organs. In the United States alone, 78,837 patients are waiting for organ donations (at the time of publication), but only 3,407 donations have been made since January 2014. Machines capable of creating functional human parts could significantly shorten — or nullify — that line. Sadly, we’re still at the early stages of the technology. As it turns out, printing working human organs is a lot more complex than printing out plastic toys.