This year he showed how, by injecting the cells into a matrix made from silica nanotubes wrapped in a sol-gel, he was able to keep a cell alive for six months.

FORBES: The Science of Small

Moreover, the basic cells that make up cartilage typically are bound in a cellular matrix where they are at, which makes them difficult to move.

FORBES: Nanofiber Spheres Allow for Tissue Regeneration

Macchiarini performed the nine-hour operation on April 9 at the Children's Hospital of Illinois after carefully creating the windpipe using stem cells from Hannah's bone marrow that were saturated over a matrix of plastic fibers shaped into a tube.

CNN: Toddler gets new windpipe from her own stem cells