Do we have the technology to build a bionic human?Do we have the technology to build a bionic human?
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Do we have the technology to build a bionic human?
11:59 04 July 2008
NewScientist.com news service
Duncan Graham-Rowe
More and more of the body is becoming, if not obsolete, then certainly
replaceable. But which of our body parts can be engineered today, and
which will we have to make do with?
Building bones
Implants that copy the simple structural job of skeletal tissue are
the easiest to build. One UK woman suffering from rheumatoid arthritis
was recently left with only two of her original joints after having
the rest replaced by metal and plastic alternatives.
Hips, teeth and vertebral discs can all be replaced, and customised to
match the patient. A 3D printer can even be used to tailor-make parts
within hours for a perfect fit, useful after accidents. One device
prints "bone" using a new porous polymer that is nearly as strong as
the real thing.
But artificial bones are not perfect. One idea that may see them match
natural bone's strength and lightness is to build implants by zapping
titanium powder with a laser. That can makes pores of different sizes
in different areas of the finished product, controlling strength and
stiffness in the same way as real bone.
Other recently developed ways to improve implants include making them
magnetic to attract drugs or giving them surface textures able to
promote new bone growth.
But growing living bone and cartilage to order is probably the best
way to tackle the problems with getting the body to accept man-made
materials.
Regeneration game
In the first human trial of this approach, lab-grown cartilage proved
able to fix damaged knees. This type of tissue-engineering cultivates
cells over a scaffold that is usually based on compounds found in
connective tissue.
Ligaments can also be grown this way. Placing a scaffold in the body
allows in-situ growth, a technique that can also work with nerves and
returned sight to blind hamsters.
In fact, by culturing normal or stem cells it is now possible to grow
pretty much any type of tissue. Some complete organs have already been
grown from scratch.
Artificially grown bladders have changed the lives of some spina
bifida patients. Even working penises have been grown, for rabbits,
who could ejaculate and successfully mate using them.
But growing more complex organs with intricate systems of blood
vessels is difficult. One possible solution involves making a plastic
cast of an organ's blood vessels by filling a donated organ with
polymer.
The recovered cast is then seeded with cells that grow into blood
vessels, after which the organs' new cells are grown over the top. A
liver complete with blood vessels has been made this way, but was not
fully functional.
Organs live on
A way to sidestep the problems of growing intricate structures like
blood vessels or alveoli in the lungs is to borrow the structures from
donated organs.
A process called "decellularisation" chemically strips away cells,
leaving connective tissue, including blood vessels, behind. This also
has the advantage that, without living cells, the transplant will not
be rejected by the host.
First used to replace heart valves, the technique was this year used
to reincarnate a whole rat's heart . After a few electric shocks, the
newly grown heart was beating regularly.
Heart helpers
That technique is still far from reaching human hospitals, but cardiac
patients are already spoilt for choice when it comes to replacements.
The most common are pacemakers, which take over from the clumps of
cells that synchronise heart muscle with pulsing electricity.
Scientists have recently developed a pacemaker powered by the heart
itself, saving later operations to change the battery.
Human heart transplants have been carried out for decades, while
artificial hearts can help people waiting for a transplant.
Other parts of the body's plumbing network, such as the lymphatic
system, are becoming replaceable too. Last year, mice were implanted
with an artificial lymph node made from collagen and cells taken from
a gland in newborn mice.
This approach could one day be used to rebuild an immune system
compromised by disease like AIDS.
Nervous reaction
The brain's complexity makes it doubtful we will ever recreate it. But
some of its functions, and those of other parts of the nervous system
can already be replaced by electronics.
The most successful example is the cochlear implant. More than 100,000
people can hear again thanks to microphone output directly stimulating
the cochlea of the inner ear.
This approach has limitations, though, so a new design stimulates the
nerve connecting the ear to the brain instead, an approach that should
offer better quality hearing and even music to the deaf.
Implants can also help the blind see, by stimulating the retina, optic
nerve or the brain's visual cortex. However, the quality of results
varies. Making better bionic eyes hinges on better understanding how
the retina and brain process images.
Perhaps the most ambitious neural implant yet attempts to replace a
whole section of the brain – the hippocampus – which is involved in
spatial and short-term memory. Researchers are working on an
electronic hippocampus that accepts, processes and produces electrical
signals just like a real one.
Out on a limb
Other research seeks to replace entire limbs with robotic
replacements. Electronics and motors must simulate bone, muscle and
nerves working in unison, and integrate smoothly with the real thing.
The Italian CyberHand project aims to let a person control and receive
sensation from an artificial hand just as they would from a real one.
Electrodes will connect the nerves that previously served the missing
hand to the robotic prosthetics motors and force sensors.
Some advanced bionic arms require the nerves that once controlled to a
missing limb be "rewired" to a person's chest. When they try to move
the prosthetic limb, it causes the chest muscles to twitch, triggering
sensors that control the arm. Rewiring the sensory nerves from a limb
in the same way makes it possible to feel feedback from the arm as if
it were real.
US defence agency DARPA has made improved prosthetics a priority, with
one funded project, the "Luke arm", recently unveiling impressive
results.
Future imperfect
Despite all these successes and promising leads, the human body is
still more complex than any machine, and we don't have the advantage
of an instruction manual.
All too often, artificial replacements come with a catch. Organ
transplants require lifetime treatment with immunosuppressant drugs to
prevent rejection, while some evidence suggests stem cells treatments
can cause cancer.
Electronic devices suffer corrosion, wear and tear, and can require
repeated operations to replace batteries. Powering them using movement
or other energy from the body could be the answer.
Electronic implants can also be vulnerable to electromagnetic
interference or even remote attacks. Earlier this year researchers
used radio waves to hack a pacemaker in a way that could cause a heart
attack.
Working out how to encourage a body to grow its own replacements
avoids most of these problems. However, superhuman abilities like
controlling machines with your thoughts will always depend on
electronics.
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