Doctors at the Xijing Hospital of the Fourth Military Medical University in Xi'an, Shaanxi province say they have used “4D printing” to reconstruct the breast of a cancer patient. The 3D printed breast implant will biodegrade over time—the fourth dimension—allowing human tissue to replace it. 3D printing in medicine is one of our most frequently covered topics. You’ll probably have noticed the articles about 3D printed skin, 3D printed ears, and everything in between. But something we write less often about is 4D printing in medicine.