Biomedical engineers from the University of California, San Diego have created a stem cell based tissue that mimics the human liver. This model could be used for patient-specific drug screening and disease modeling. The complex micro-architecture of a liver utilized a hexagonal pattern of stem cells and human liver tissue. Autologous stem cells were taken from the patient’s own skin cells to act as supporting cells. Because the method used 3D printing, the entire structure—a 3 × 3 millimeter square, 200 micrometers thick—takes just seconds to print on demand.