SFGate looks at ongoing work in replicating the function of a kidney: "The artificial kidney is still at least five years away from being tested in a human patient. Researchers have built a large model of the kidney - so big that it filled a hospital room - and used it on human patients to show that the theories behind it will work. And parts of the small kidney have been successfully tested in animals. If [the] team is successful, the kidney will be about the size of a large cup of coffee, and it would last for years, maybe decades, and require no pumps or batteries. Patients wouldn't need anti-rejection drugs either, because there would be no exposed natural tissues for the immune system to attack. ... The artificial kidney will be made of two parts - a filter side and a cellular side. On the filter side, silicone membranes with microscopic pores will separate toxins from the blood, much as dialysis machines do. The body's own blood pressure will force blood through the filter, so no pumps will be needed. The key to the filtration side is the silicone membrane, which can be made fairly inexpensively and precisely, much as computer chips are. ... On the cellular side, the filtered blood will be pumped over a bed of cells taken from either the patient's own failing kidneys or from a donor. The cells will sense the chemical makeup of the filtered blood and trigger the body to maintain appropriate levels of salt, sugar and water. ... It mimics more of a kidney function than just dialysis. When we think of kidneys, we think of waste removal. And dialysis just does that. Dialysis doesn't make you healthy - it just keeps you alive."