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
Human artificial chromosome Human artificial chromosome A human artificial chromosome (HAC) is a microchromosome that can act as a new chromosome in a population of human cells. That is, instead of 46 chromosomes, the cell could have 47 with the 47th being very small, roughly 6–10megabases (Mb) in size instead of 50–250Mb for natural chromosomes, and able to carry new genes introduced by human researchers. Ideally, researchers could integrate different genes that perform a variety of functions, including disease defense. Alternative methods of creating transgenes, such as utilizing yeast artificial chromosomes and bacterial artificial chromosomes, lead to unpredictable problems. The genetic material introduced