Bioprinting builds living tissue layer by layer using bio-ink made of cells and hydrogels, with techniques including extrusion, inkjet, and laser-assisted printing. It is a promising answer to the shortage of organ donors. Cell survival drops sharply beyond roughly 60–300 μm from a capillary, which is why blood vessels are the main barrier to printing whole organs. Printed tissues are already used for drug testing and disease modeling, and research is moving toward printing directly at the injury site during surgery.