DIALYSIS is not as bad as dying, but it is pretty unpleasant, nonetheless. It involves being hooked up to a huge machine, three times a week, in order to have your blood cleansed of waste that would normally be voided, via the kidneys, as urine. To make matters worse, three times a week does not appear to be enough. Research now suggests that daily dialysis is better. But who wants to tied to a machine—often in a hospital or a clinic—for hours every day for the rest of his life?

Victor Gura, of the University of California, Los Angeles, hopes to solve this problem with an invention that is now undergoing clinical trials. By going back to basics, he has come up with a completely new sort of dialyser—one you can wear.

A traditional dialyser uses around 120 litres of water to clean an individual's blood. This water flows past one side of a membrane while blood is pumped past the other side. The membrane is impermeable to blood cells and large molecules such as proteins, but small ones can get through it. Substances such as urea (a leftover from protein metabolism) and excess phosphate ions therefore flow from the blood to the water. The good stuff, such as sodium and chloride ions, stays in the blood because the cleansing water has these substances dissolved in it as well, and so does not absorb more of them.

Both water and blood require a lot of pumping. Those pumps are heavy and need electrical power. The first thing Dr Gura did, therefore, was dispose of them. The reason for using big pumps is to keep dialysis sessions short. If machines are portable that matters less. So Dr Gura replaced the 10kg pumps of a traditional machine with small ones weighing only 380 grams. Besides being light, these smaller pumps use less power. That means batteries can be employed instead of mains electricity—and modern lithium-ion batteries, the ones Dr Gura chose, are also light, and thus portable.

To reduce the other source of weight, the water, Dr Gura and his team designed disposable cartridges containing materials that capture toxins from the cleansing water, so that it can be recycled. The upshot is a device that weighs around 5kg and can be strapped to a user's waist. Indeed, at a recent demonstration in London, one patient was able to dance while wearing the dialyser—for joy, presumably, at no longer having to go to hospital so often.