Artificial organ almost always preceded by extensive experiments with animals. Initial testing in humans is frequently limited to those either already facing death or who have exhausted every other treatment possibility. Artificial arms and legs, or prosthetics, are intended to restore a degree of normal function to amputees. Mechanical devices that allow amputees to walk again or continue to use two hands have probably been in use since ancient times, the most notable one being the simple peg leg. Since then, the development of artificial limbs has progressed rapidly. New plastics and other materials, such as carbon fiber have allowed artificial limbs
Effect of spaceflight on the human body problems could be a major concern for future deep space flight missions, including a manned mission to the planet Mars. If indeed elevated intracranial pressure is the cause, artificial gravity might present one solution, as it would for many human health risks in space. However, such artificial gravitational systems have yet to be proven. More, even with sophisticated artificial gravity, a state of relative microgravity may remain, the risks of which remain unknown. One effect of weightlessness on humans is that some astronauts report a change in their sense of taste when in space. Some astronauts find that their food