MAKING A BIT OF ME
Feb 18th 2010, The Economist
A machine that prints organs is coming to market
THE great hope of transplant surgeons is that they will, one day, be
able to order replacement body parts on demand. At the moment, a
patient may wait months, sometimes years, for an organ from a suitable
donor. During that time his condition may worsen. He may even die. The
ability to make organs as they are needed would not only relieve
suffering but also save lives. And that possibility may be closer with
the arrival of the first commercial 3D bio-printer for manufacturing
human tissue and organs.
The new machine, which costs around $200,000, has been developed by
Organovo, a company in San Diego that specialises in regenerative
medicine, and Invetech, an engineering and automation firm in
Melbourne, Australia. One of Organovo's founders, Gabor Forgacs of the
University of Missouri, developed the prototype on which the new 3D
bio-printer is based. The first production models will soon be
delivered to research groups which, like Dr Forgacs's, are studying
ways to produce tissue and organs for repair and replacement. At
present much of this work is done by hand or by adapting existing
instruments and devices.
To start with, only simple tissues, such as skin, muscle and short
stretches of blood vessels, will be made, says Keith Murphy, Organovo's
chief executive, and these will be for research purposes. Mr Murphy
says, however, that the company expects that within five years, once
clinical trials are complete, the printers will produce blood vessels
for use as grafts in bypass surgery. With more research it should be
possible to produce bigger, more complex body parts. Because the
machines have the ability to make branched tubes, the technology could,
for example, be used to create the networks of blood vessels needed to
sustain larger printed organs, like kidneys, livers and hearts.
PRINTING HISTORY
Organovo's 3D bio-printer works in a similar way to some
rapid-prototyping machines used in industry to make parts and
mechanically functioning models. These work like inkjet printers, but
with a third dimension. Such printers deposit droplets of polymer which
fuse together to form a structure. With each pass of the printing
heads, the base on which the object is being made moves down a notch.
In this way, little by little, the object takes shape. Voids in the
structure and complex shapes are supported by printing a "scaffold" of
water-soluble material. Once the object is complete, the scaffold is
washed away.
Researchers have found that something similar can be done with
biological materials. When small clusters of cells are placed next to
each other they flow together, fuse and organise themselves. Various
techniques are being explored to condition the cells to mature into
functioning body parts--for example, "exercising" incipient muscles
using small machines.
Though printing organs is new, growing them from scratch on scaffolds
has already been done successfully. In 2006 Anthony Atala and his
colleagues at the Wake Forest Institute for Regenerative Medicine in
North Carolina made new bladders for seven patients. These are still
working.
Dr Atala's process starts by taking a tiny sample of tissue from the
patient's own bladder (so that the organ that is grown from it will not
be rejected by his immune system). From this he extracts precursor
cells that can go on to form the muscle on the outside of the bladder
and the specialised cells within it. When more of these cells have been
cultured in the laboratory, they are painted onto a biodegradable
bladder-shaped scaffold which is warmed to body temperature. The cells
then mature and multiply. Six to eight weeks later, the bladder is
ready to be put into the patient.
The advantage of using a bioprinter is that it eliminates the need for
a scaffold, so Dr Atala, too, is experimenting with inkjet technology.
The Organovo machine uses stem cells extracted from adult bone marrow
and fat as the precursors. These cells can be coaxed into
differentiating into many other types of cells by the application of
appropriate growth factors. The cells are formed into droplets 100-500
microns in diameter and containing 10,000-30,000 cells each. The
droplets retain their shape well and pass easily through the inkjet
printing process.
A second printing head is used to deposit scaffolding--a sugar-based
hydrogel. This does not interfere with the cells or stick to them. Once
the printing is complete, the structure is left for a day or two, to
allow the droplets to fuse together. For tubular structures, such as
blood vessels, the hydrogel is printed in the centre and around the
outside of the ring of each cross-section before the cells are added.
When the part has matured, the hydrogel is peeled away from the outside
and pulled from the centre like a piece of string.
The bio-printers are also capable of using other types of cells and
support materials. They could be employed, Mr Murphy suggests, to place
liver cells on a pre-built, liver-shaped scaffold or to form layers of
lining and connective tissue that would grow into a tooth. The printer
fits inside a standard laboratory biosafety cabinet, for sterile
operation. Invetech has developed a laser-based calibration system to
ensure that both print heads deposit their materials accurately, and a
computer-graphics system allows cross-sections of body parts to be
designed.
Some researchers think machines like this may one day be capable of
printing tissues and organs directly into the body. Indeed, Dr Atala is
working on one that would scan the contours of the part of a body where
a skin graft was needed and then print skin onto it. As for bigger body
parts, Dr Forgacs thinks they may take many different forms, at least
initially. A man-made biological substitute for a kidney, for instance,
need not look like a real one or contain all its features in order to
clean waste products from the bloodstream. Those waiting for
transplants are unlikely to worry too much about what replacement body
parts look like, so long as they work and make them better.
)-0.6%
