Artificial kidney and hearts
are fairly easy to design, but not so for livers
and lungs because their structures and functions
are so complex. The complexity of these organs
prevent artificial substitutes from coming into
existance for a number of years.
A liver, for instance is a
place where many chemical reactions take place.
It removes and adds substances to the blood and
changes more into different substances.
Recently, however, there
have been commercial websites which advertise a
new liver machine which acts like a dialysis
machine, and performs most major functions of the
liver, including heating it. This buys time for
the liver to recover.
As always, present and future procedures face to problem of infection. Any break in the skin allows dangerous microbes into the body's system and despite great strides in [antisepsis] and [asepsis], some microorganisms are resistant to drugs.
Another problem is that rejection, the body's reaction to foreign materials placed in it. This reaction may take the form of blood clots, attempts to dissolve the foreign material, or attacks by the immune system.
Although transplanted natural organs are preferred to artificial ones, the number of people who need transplants exceeds the number of organs available. On top of that, the immune system's response to foreign tissue, is more often than not, more violent than a reaction towards something inorganic.
Some people may also be too old to recieve transplants, in which case permanant artificial organs may be their only hope.