Artificially constructed human organs on the horizon?
The liver is arguably one of the most complex organs in the body due to the list of functions it carries out. Not only does it help to filter the blood but it synthesizes an array of proteins, strips worn erythrocytes out of the bloodstream, and produces a number of hormones. That's just the first page of the list. It's also unusual in that it is capable of regenerating and becoming fully functional once again given enough time and proper conditions. Except when it doesn't; there are a number of diseases and chronic conditions that can render the liver nonfunctional, at which time the patient's only hope is really a transplant. Unfortunately there aren't many livers to go around; even when you factor in its ability to regenerate the immune system will still recognize it as foreign tissue and attack it mercilessly (the condition known as rejection).
Thus, it is certainly worth noting that the Institute for Regenerative Medicine at Wake Forest Baptist Medical Center has succeeded in growing miniature livers under laboratory conditions (thanks to grinding.be for the heads-up). The prototypes were grown using the collagen scaffoldings from decellularized animal livers and then impregnated with human progenitor liver cells as well as endothelial cells found in human blood vessels through the existing circulatory system. The detergent used in the decellularization process leaves the network of blood vessels intact while removing the other cells. The prototype organs-to-be were then installed into a bioreactor and allowed to grow under conditions as close to the interior of the human body as possible. After just a week in the growth medium not only had the seeded cells begun to differentiate into the expected structures but the prototypes began showing signs of normal liver operation. It's not yet known whether or not the engineered organs would actually function in the same fashion as a natural liver, animal trials, a run of the FDA gauntlet, and a battery of clinical trials will be necessary to tell for sure.
It looks like the Wake Forest Institute for Regenerative Medicine is fast becoming a hub of bioengineering research because a separate project at the institute recently presented research dealing with a most unique 3D printer, only instead of extruding molten plastic its feedstock consists of skin cells. While skin grafts are relatively easy to harvest and implant they tend not to last too long unless they came from the patient; most of the time they're used to cover burned flesh until the patient's own skin develops to the point where it'll cover the injured areas. The printer is designed so that you can put an injured limb inside of it, whereupon it sprays a mixture of coagulants, fibrin precursors, and skin cells in solution over the area. Rodent tests were extremely promising, showing closure of surgical wounds and formation of scar tissue in as little as three weeks. Unfortunately there is no word yet on whether or not sensory nerve endings regenerated, or what it felt like after the scar tissue began to form. Hopefully the damaged nerves weren't misfiring constantly.