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The irst stem cells identiied in the 1980s were extracted from the tissue
of unborn human fetuses, triggering emotional debates about medical ethics.
Since then, researchers continue to uncover more stem cells, including some
scattered around different parts of the adult human body called “somatic” or
“adult” stem cells. More recently, some differentiated cells have been shown
even to be able to revert back to their pre-differentiated state.
Columbia professor Jeremy Mao 3D printed new hip bones in lab rabbits
and seeded them with stem cells. First, Mao and his team removed and imaged
the hip bones of lab rabbits. They converted the images to a working design
ile, 3D printed the hip replacements out of artiicial bone, then sprinkled the
artiicial bone with the rabbit's stem cells and surgically inserted the bone
back inside the rabbit. By the end of 4 months, all the rabbits were walking
freely, some even placing weight on their new hips a few weeks after surgery.
Mao and his research team designed the replacement bone with tiny curv-
ing inner micro channels that encouraged the stem cells to creep along the
implant's surface and help the rabbit heal more quickly. In other experiments,
Mao's team printed out a replacement incisor for a lab rat, sprinkled it with
stem cells and implanted the replacement back into the jaw. Nine weeks later,
thanks to the incisor's ideal shape and stem cell infusion, new ligaments and
bone embraced the artiicial tooth.
Similar to the approach used by Dr. Mao's team at Columbia University,
researchers at Washington State University 3D printed bone using a ine misty
spray made of calcium phosphate, silicon, and zinc powder. The ine spray
droplets created layers 20 microns thick (half the width of a human hair). The
printed bone was sprinkled with immature human bone cells. The method
worked, as the immature bone cells thrived in their new environment and
eventually grew into mature, living bone tissue.
Stem cells, bio-ink, and bio-paper
A medical dictionary deines tissue as “an aggregation of similarly specialized
cells which together perform certain special functions.” Our bodies are made
up of different types of tissue, from adipose tissues that form our fat cells, to
cartilaginous tissue that form cartilage to cushion our joints, to nervous tissue
made up of complex networks of connected neurons. Soft tissues hold their
shape thanks to an internal supportive infrastructure.
When we can print living cells and make them grow into living tissue,
we will have successfully ascended to the top rungs of the hypothetical 3D
