Mouse with Human Ear / Or Not?

The "mouse-ear" project began in 1989, when Charles Vacanti (brother of Joseph) managed to grow a small piece of human cartilage on a biodegradable scaffold. The scaffold was the same synthetic material (99% polyglycolic acid and 1% polylactic acid) used in dissolving surgical stitches. In the body, it degrades into carbon dioxide and water. The fibres of this material were woven into a loose mesh that was 97% air - leaving lots of room for cells to grow into. His surgeon colleagues had told him that the human ear was the body's most difficult cartilaginous tissue to reconstruct and rebuild - and that they would love to have a "spare" ear to transplant.

After 8 years, Charle's team got to the stage where they could mould their sterile biodegradable mesh into the exact shape of a 3 year-old's ear. The next step was to seed this ear-shaped scaffold with cartilage cells from the knee of a cow (remember how I said that the famous mouse-ear had absolutely no human cartilage cells in it). The team used a Nude Mouse. The Nude Mouse got its name thanks to a random mutation in the 1960s that left the mouse with no hair, and virtually no immune system. The lack of hair was irrelevant to their project, but the lack of immune system was critical. It meant that the mouse would not reject the foreign cow cartilage cells. The only purpose of the mouse in this project was to supply power to let the cow cartilage cells grow. The cartilaginous ear was implanted under the skin layer of the mouse, but over the muscle layer. Over some three months, the mouse grew extra blood vessels that nourished the cow cartilage cells, that then grew and infiltrated into the biodegradable scaffolding (which had the shape of a human ear). By the time that the scaffolding had dissolved away, the cartilage had enough structural integrity to support itself.

That cartilaginous structure that looked like a human ear was never transplanted onto a human, because it was full of cow cells and would have been rejected by a person's immune system.