Why a dialysis machine does not count as an artificial kidney
A dialysis machine does nearly all of a failing kidney's work, yet by the usual definition it is not an artificial organ. To qualify, a device must live with the body and not stay tethered to a fixed power supply, filter or chemical plant. By that standard a replacement hip counts, while a lifesaving room-sized machine does not.
Prosthetic limbs are the oldest example; the humble peg leg goes back to ancient times. Carbon fibre and new plastics have made modern limbs lighter and stronger, so wearers spend less energy moving them, and some now connect to the nervous system through electrodes placed in nerves or muscles, letting the brain steer them after training.
Hearing and sight show how far the field has come and how far it has to go. A cochlear implant skips most of the outer and middle ear: a microphone and electronics behind the ear send signals to electrodes inside the cochlea, which stimulate the hearing nerve directly. Artificial eyes lag far behind. The best pair a miniature camera with an implant on the retina, optic nerve or brain, and deliver only rough impressions such as brightness, patches of colour and simple shapes, partly because the real retina does complex image processing before signals ever reach the brain.
Blood itself is a target. Thomas Chang and Poznanski made the first artificial red blood cell in 1968, able to carry oxygen and carbon dioxide, and interest surged when donated blood contaminated with HIV became a crisis. A newer design, one-fiftieth the size of a natural cell, wraps purified human haemoglobin in a polymer coat that grabs oxygen when blood is less acidic and lets go when it is more acidic, and it is meant to suit any blood type.
Printing is another frontier. At Massachusetts General Hospital, Thomas Cervantes and colleagues used a 3D printer and sheep cartilage to build an ear shaped like a human one, aiming at microtia, where the outer ear fails to form. In 2017 an NIH-backed study implanted 3D-printed ovaries in sterile mice. Lab-grown hearts are still held back by the difficulty of making blood vessels and tissue work together.
Source: Artificial organ
