Like other organs, eyes sometimes need to be replaced with a transplant, and that transplant comes from a person who agreed to donate their organs upon their death. In the future, it might be a lot easier to acquire an eye transplant thanks to 3D printing. University of Cambridge researchers published a paper today detailing how they used an ink printer to print multiple types of rat eye cells; the first time anyone has been able to keep eye cells healthy and at the right consistency to flow out of a nozzle.