3D bio-printing is a process that uses 3D printing technologies to create cell patterns in a confined space while preserving cell function and viability. It works by layering cells and nutrients to create tissue-like structures for medical and tissue engineering uses. Some key developments include the first artificial bladder and trachea being printed in 2006 and 2011. The 3D bio-printing process generally involves pre-bioprinting to create a model, bioprinting to structure cells using patient scans, and post-bioprinting to create stability. Applications include using bio-printed tissues for transplants, drug research, and eventually fully functional human organs.