How to 3D print human tissue Taneka Jones
There are currently hundreds of thousands
of people on transplant lists,
waiting for critical organs like kidneys,
hearts, and livers
that could save their lives.
Unfortunately,
there aren’t nearly enough donor organs
available to fill that demand.
What if instead of waiting,
we could create brand-new, customized
organs from scratch?
That’s the idea behind bioprinting,
a branch of regenerative medicine
currently under development.
We’re not able to print complex
organs just yet,
but simpler tissues including blood
vessels and tubes
responsible for nutrient
and waste exchange
are already in our grasp.
Bioprinting is a biological
cousin of 3-D printing,
a technique that deposits layers of
material on top of each other
to construct a three-dimensional object
one slice at a time.
Instead of starting with metal, plastic,
or ceramic,
a 3-D printer for organs and
tissues uses bioink:
a printable material that
contains living cells.
The bulk of many bioinks are water-rich
molecules called hydrogels.
Mixed into those are
millions of living cells
as well as various chemicals that
encourage cells to communicate and grow.
Some bioinks include a
single type of cell,
while others combine several different
kinds to produce more complex structures.
Let’s say you want to print a meniscus,
which is a piece of cartilage in the knee
that keeps the shinbone and thighbone
from grinding against each other.
It’s made up of cells called chondrocytes,
and you’ll need a healthy supply of
them for your bioink.
These cells can come from donors whose
cell lines are replicated in a lab.
Or they might originate from a
patient’s own tissue
to create a personalized meniscus less
likely to be rejected by their body.
There are several printing techniques,
and the most popular is extrusion-based
bioprinting.
In this, bioink gets loaded into a
printing chamber
and pushed through a round nozzle
attached to a printhead.
It emerges from a nozzle that’s rarely
wider than 400 microns in diameter,
and can produce a continuous filament
roughly the thickness
of a human fingernail.
A computerized image or file guides the
placement of the strands,
either onto a flat surface or into a
liquid bath
that’ll help hold the structure in place
until it stabilizes.
These printers are fast, producing the
meniscus in about half an hour,
one thin strand at a time.
After printing, some bioinks
will stiffen immediately;
others need UV light or an additional
chemical or physical process
to stabilize the structure.
If the printing process is successful,
the cells in the synthetic tissue
will begin to behave the same way
cells do in real tissue:
signaling to each other, exchanging
nutrients, and multiplying.
We can already print relatively simple
structures like this meniscus.
Bioprinted bladders have also been
successfully implanted,
and printed tissue has promoted facial
nerve regeneration in rats.
Researchers have created lung tissue,
skin, and cartilage,
as well as miniature, semi-functional
versions of kidneys, livers, and hearts.
However, replicating the complex
biochemical environment
of a major organ
is a steep challenge.
Extrusion-based bioprinting may destroy
a significant percentage of cells in the
ink if the nozzle is too small,
or if the printing pressure is too high.
One of the most formidable challenges
is how to supply oxygen and nutrients
to all the cells in a full-size organ.
That’s why the greatest successes so far
have been with structures
that are flat or hollow—
and why researchers are busy
developing ways
to incorporate blood vessels
into bioprinted tissue.
There’s tremendous potential to use
bioprinting
to save lives and advance our
understanding
of how our organs function
in the first place.
And the technology opens up a dizzying
array of possibilities,
such as printing tissues with
embedded electronics.
Could we one day engineer organs that
exceed current human capability,
or give ourselves features like
unburnable skin?
How long might we extend human life
by printing and replacing our organs?
And exactly who—and what—
will have access to this technology
and its incredible output?